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The Evolution of Racial Pelvis Variation

1850 words

It’s well-known that blacks have narrower hips than whites (Rushton, 1997; Handa et al, 2008). These pelvic differences then account for part of the variation in elite sporting events such as sprinting and jumping (Entine, 2000). These pelvic differences are the result of climatic variation and sexual selection.

The evolution of the pelvis is due to bipedalism. We are bipeds because of our S-shaped spine, which helps us to cope with differing loads. The human pelvis had to evolve in two ways—to make birthing babies easier and to become more efficient for bipedal walking. Termed the ‘obstetric dilemma’, it has implications for osteoarthritis in both men and women (Hogervorst, Heinse, and de Vos, 2009). Having a more efficient bipedal gait meant the body could allocate energy to other parts of the body—mainly our growing brains/neuronal count. Over time, the brain grew while the pelvis had to shrink for more efficient bipedalism. The pelvis also got narrower in our evolution, being wider in Australopithicenes, while becoming more narrow when erectus appeared—which is the first instance of a humanlike pelvis in the fossil record—which increased how far we could travel as well as reduce our energy expenditure (Lieberman, et al, 2006). Further discussion can be found in my article Man the Athlete.

So we began evolving a narrower pelvis in comparison to our ancestors because it was more efficient for heat dissipation. Smaller trunks are more efficient for heat dissipation (Lieberman, 2015), whereas wider trunks are more efficient for thermoregulation in colder climes (Weaver and Hublin, 2008; Weaver, 2009; Gruss and Schmidt, 2015). Now, simply applying this logic to Eurasians and Africans (I am grouping East Asians and Europeans together since they were a single breeding population up until about 23,000-6,500ya), we can see one reason why that population has wider pelves than Africans.

When anatomically modern humans (AMH) left Africa between 50-100kya, human skeletal morphology was just like modern-day Africans’ today. When Man migrated into northerly climes, however, a wider pelvis was needed to retain heat in colder climes (Gruss and Schmidt, 2015). So, along with a wider pelvis evolving due to climatic demands on the body, as we migrated north the human brain expanded due to the climate of the area, along with expanding the pelvis to better thermoregulate (which a bigger brain also does in northerly climes). I did argue two months back (and added to Skoyles’ (1999) theory) that brain size increased for expertise capacity and not IQ since Arctic people needed more tools, as well as tools that were more complex, in comparison to peoples who evolved in a hotter climate. So selection then occurred for larger brains and pelvis due to the demand for thermoregulation and bigger brains—which then led to earlier births and more helpless babes, which higher levels of intelligence were then needed to care for them (Piantadosi and Kidd, 2016). The helplessness of infants predicts the intelligence of adults in the primate genera (Piantadosi and Kidd, 2016), so I will assume that this holds within primate species as well (I am not able to locate a citation that this doesn’t hold within the primate genera; if I am in error, please provide a citation). Since African children are born earlier and  more mature than Eurasian children who are born slightly later and more helpless/less developed, this is one reason why Eurasians have higher levels of intelligence than Africans (which is independent of any direct effects of climate I may add!).

So since Eurasians needed a larger brains to make more tools in the Arctic/colder climes, their brains needed to expand in size for increased expertise capacity, which would then have further selected for wider pelves in Eurasian women. Climatic variation caused the wider hips/bigger brains in Eurasians, which then allowed the evolution of larger brains in comparison to those who remained in Africa.

Finally, the obstetric dilemma has been recently called into question; there is evidence that a wider pelvis does not increase locomotor costs in humans (Warrener et al, 2015), a treadmill tracked their gait, as well as the motion of their pelvis. This study is used as evidence that the obstetric dilemma is wrong—they argue that there is no trade-off between narrower hips in men and wider hips in women.  However, as the authors point out, all subjects in the study walked/ran at the same speed. Let’s say that the speed was heightened; do you think the women/men with wider pelves would have had the same locomotor costs as the men/women with narrower pelves? The answer is, obviously, no.

The pelvis of all of the races of Man has evolved the way they are due to environmental/climatic demands. A wider pelvis is better for thermoregulation in colder climates, while a narrower pelvis/body is more efficient for heat loss (Gruss and Schmidt, 2015).

Thus, we can look at the evolution of brain size/pelvic size in a few ways: 1) The amount of tools/complexity of the tools in the area that led to a need for an increase in brain size for more ‘chunks’ (Gobet and Simon, 1998), which then—along with colder climates—selected for larger brains and a wider body/pelvis which made birthing babes with large heads/brains easier along with helping to conserve heat due to the wider body (Gruss and Schmidt, 2015); 2) Since people in higher altitudes needed a high amount of expertise to survive, further selection for bigger brains, wider pelves occurred because of this; 3) Africans have smaller pelves in comparison to Eurasians because they evolved in hotter climes and didn’t have the amount of tools that peoples in more northerly climes did—which also increased brain size; 4) putting this all together, we can say that because Africans live in hotter climates, they need narrow pelves in order to lose body heat; Eurasians, after they migrated into more northerly climes, needed a wider body/pelvis in order to retain heat. When Man migrated north, he needed the ability to become an expert in, say, tool-making and thus needed a bigger brain for more informational chunks (Simon and Gobet, 1998; Skoyles, 1999). Due to this, Eurasians have wider pelves since they needed larger brains for a higher expertise capacity (Skoyles, 1999).

When Man migrated north, he needed the ability to become an expert in, say, tool-making and thus needed a bigger brain for more informational chunks (Simon and Gobet, 1998; Skoyles, 1999). Due to this, Eurasians have wider pelves than Africans; so they can birth larger-brained children. The width of the female pelvis, too, was shaped by sexual selection (Lassek and Gaulin, 2009). Therefore, the evolution of the modern pelvis in human populations comes down to climatic variation, which, in turn, affects how large of a brain the babe is able to have. Climate constrains brain size in either ‘direction’, big or small. We don’t even need to look at the variation within modern Homo sapiens to see the pattern in pelvic size we do today; because the pelvic differences noted among Man definitely were in effect millions of years ago, with hominids in colder climates having wider pelves while hominids in warmer climates had narrower pelves.

Along with everything above, the evolution of the human pelvis has a few implications for the human races today. Some recent studies have shown that there is no obstetric dilemma at all, with birth complications being caused by babies with higher weights than in our ancestral past, due to environmental mismatches causing higher-weight babies (Warrener et al, 2015; Betti, 2017), which was also beneficial for the evolution of our large brains (Cunnane and Crawford, 2003) with the largest amount of cortical neurons in the animal kingdom. However, marked differences in locomotion would be seen in people who had wide pelves compared to narrow pelves; which is what we see in elite running competitions: the elite runners have narrower pelves. So wider pelves don’t impede normal bipedal walking, but it does impede being able to efficiently run, as evidenced in participants of elite sprinting and marathon competitions. Looking at champion athletes and studying their locomotion (along with other traits as I’ve covered here) you can see that those with narrower pelves win more competitions than those with wider pelves (and happen to have different muscle fiber competition, fat distribution/percent, and morphology).

Racial differences in the pelvis explain the reasons behind why a certain race dominates in certain elite competitions; it largely comes down to skeletal morphology. These skeletal differences have evolutionary underpinnings, with the same pelvic differences seen in hominins that evolved in colder/warmer climates in the past. These pelvic differences (along with body fat percentage/distribution, musculoskeletal morphology, muscle fiber type, lean mass percentage, lower Vo2 max, poorer running economy, a larger Q-angle [4.6 degrees greater than men], etc) are why women are less efficient runners. People with wider hips are more likely to have be endomorphic while people with narrower hips are more likely to be ecto and meso. Not surprisingly, people from northerly climes consistently win WSM competitions whereas East and West Africans dominate bodybuilding and sprinting/marathons due to having a narrower pelvis and other advantageous morphological traits that lead to success in the sport. Nevertheless, pelvic differences between the races largely come down to differences in climate, which was also seen in ancient hominins. These pelvic differences further lead to racial differences in elite sporting competition.

References

Betti, L. (2017). Human Variation in Pelvic Shape and the Effects of Climate and Past Population History. The Anatomical Record,300(4), 687-697. doi:10.1002/ar.23542

Cunnane, S. C., & Crawford, M. A. (2003). Survival of the fattest: fat babies were the key to evolution of the large human brain. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology,136(1), 17-26. doi:10.1016/s1095-6433(03)00048-5

Dr. John R. Skoyles (1999) HUMAN EVOLUTION EXPANDED BRAINS TO INCREASE EXPERTISE CAPACITY, NOT IQ. Psycoloquy: 10(002) brain expertise

Entine, J. (2000). Taboo: why Black athletes dominate sports and why we are afraid to talk about it. New York: PublicAffairs.

Gobet, F., & Simon, H. A. (1998). Expert Chess Memory: Revisiting the Chunking Hypothesis. Memory,6(3), 225-255. doi:10.1080/741942359

Gruss, L. T., & Schmitt, D. (2015). The evolution of the human pelvis: changing adaptations to bipedalism, obstetrics and thermoregulation. Philosophical Transactions of the Royal Society B: Biological Sciences,370(1663), 20140063-20140063. doi:10.1098/rstb.2014.0063

Hogervorst, T., Heinse W.B., & de Vos J., (2009) Evolution of the hip and pelvis. Acta Orthopaedica, 80:sup336, 1-39, DOI: 10.1080/17453690610046620

Lieberman, D. E., Raichlen, D. A., Pontzer, H., Bramble, D. M., & Cutright-Smith, E. (2006). The human gluteus maximus and its role in running. Journal of Experimental Biology,209(11), 2143-2155. doi:10.1242/jeb.02255

Lieberman, D. E. (2015). Human Locomotion and Heat Loss: An Evolutionary Perspective. Comprehensive Physiology, 99-117. doi:10.1002/cphy.c140011

Piantadosi, S. T., & Kidd, C. (2016). Extraordinary intelligence and the care of infants. Proceedings of the National Academy of Sciences,113(25), 6874-6879. doi:10.1073/pnas.1506752113

Rushton J P (1997). Race, Evolution, and Behavior. A Life History Perspective (Transaction, New Brunswick, London).

Handa, V. L., Lockhart, M. E., Fielding, J. R., Bradley, C. S., Brubakery, L., Cundiffy, G. W., … Richter, H. E. (2008). Racial Differences in Pelvic Anatomy by Magnetic Resonance Imaging. Obstetrics and Gynecology, 111(4), 914–920.

Warrener, A. G., Lewton, K. L., Pontzer, H., & Lieberman, D. E. (2015). A Wider Pelvis Does Not Increase Locomotor Cost in Humans, with Implications for the Evolution of Childbirth. PLoS ONE, 10(3), e0118903.

Weaver, T. D., & Hublin, J. (2009). Neandertal birth canal shape and the evolution of human childbirth. Proceedings of the National Academy of Sciences,106(20), 8151-8156. doi:10.1073/pnas.0812554106

Weaver, T. D. (2009). The meaning of Neandertal skeletal morphology. Proceedings of the National Academy of Sciences,106(38), 16028-16033. doi:10.1073/pnas.0903864106

The Evolutionary Puzzle of Floresiensis

1600 words

Back in October, I wrote that floresiensis is either descended from Erectus or habilis, since those were the only two hominins in the region. Yesterday a study was published titled The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters (Argue et al, 2017), in which Argue et al argue that floresiensis was not descended from a shipwrecked Erectus, as is a popular view. Another theory is that floresiensis is descended from habilis. The third theory is that floresiensis is Homo sapiens with a pathology, but that has been disproven (Falk et al, 2009). It was commonly thought that the LB1 floresiensis specimen was a pathological human inflicted with Laron syndrome which is a type of growth hormone deficiency (Laron and Klinger, 1994).

Argue et al found that floresiensis and erectus had completely different bone structures, particularly in the pelvis and jaw. They now believe that the theory that floresiensis is a derived form of an erectus that swam or rafted to Flores has been defintively refuted. They found that floresiensis was a sister species to habilis. So either a common ancestor of floresiensis or habilis swam to Flores from Africa, or floresiensis evolved in Africa and swam to Flores. They used new phylogenetic techniques to ascertain that floresiensis is stil a part of our lineage, but shows no phylogenetic relationship to erectus on the tree.

According to Baab (2016), biogeography shows that Indonesian erectus is the best fit with what is currently known. She says if floresiensis was derived from erectus that it “implies some degree of body size reduction and more marked brain size reduction.”

Kubo, Kono, and Kaifu (2013) conclude that the evolution of floresiensis from early Javanese erectus is possible when comparing the brain cases of both specimens. However, if floresiensis descended from habilis, then the brain size reduction wouldn’t be as marked (and is still due to island dwarfism, just not on as large of a scale as it would be if floresiensis were descended from erectus). The LB1 specimen also shows the closest neural affinities to early Asian erectus (Baab, Mcnulty, and Harvati, 2013; but see Vannuci, Barron, and Holloway, 2013 for the microcephalic view). Weston and Lister, (2009) showed that there was a 30 percent reduction in brain size in Magalasy hippos, which lends credence to the insular dwarfism hypothesis for floresiensis. Craniofacial morphology also shows that floresiensis evolved from Asian erectus (Kaifu et al, 2011).

The teeth of unknown hominin found at Mata Menge are intermediate between floresiensis and erectus, being 600,000 years older than where floresiensis was found (van den Bergh et al, 2016). This lends credence to the hypothesis that floresiensis is derived from erectus. Furthermore, insular dwarfism is seen in primate species isolated on islands, with changes in body size seen in child populations even on large islands not far from the mainland (Bromham and Cardillo, 2007, Welch, 2009). Genetically isolated on islands, primates can become bigger if the parent population was smaller, or smaller if the parent population was bigger. This is due to differing energy demands relative to the parent population, along with differing predators/prey.

The island rule even holds in the deep sea. As is the case with islands, the deep sea is also associated with decreased food availability. Looking at several species of gastropods, McClain, Boyer, and Rosenberg (2006) found that the island rule held in small-bodied shallow species. They were found to have larger bodied deep-sea representatives, with the same being true for large bodied deep-sea gastropods. Further, island dwarfism in elephants on the islands Sicily, Malta, Cyprus; mammoths on the California channel islands; and red deer on the island Jersey involved body mass changes of 5- to 100-fold over 2,300 to 120,000 generations (Evans et al, 2012).

So the overall hypothesis that island dwarfism is still intact, albeit if floresiensis is derived from habilis, the reduction in brain/body size would be smaller than if floresiensis evolved from early Asian erectus.

Further evidence for brain/body size reduction due to less food availability is noted by Daniel Lieberman in his book The Story of the Human Body: Evolution, Health, and Disease (Lieberman, 2013). While talking about the evolution of floresiensis on page 123 he writes:

The same energetic constraints and processes also affect hunter-gatherers . 62

And in the 62nd footnote on page 391 he writes:

Several human “pygmy” populations (people whose height does not exceed 150 centimeters, or 4.9 feet) have evolved in energy limited places like rain forests or islands. Perhaps the small size of the Dmansi hominins from Georgia also reflected selection to save energy among the first colonists of Eurasia.

Either way, if floresiensis evolved from erectus or habilis, considerable reductions in brain size have to be explained, since the smallest erectus brain ever found is 600 cubic centimeters while the smallest habilis brain ever found is 510 cubic centimeters (Lieberman, 2013: 124), with floresiensis having a brain 417 cubic centimeters (Falk et al, 2007).

What is most important about the insular dwarfism hypothesis in regards to the evolution of floresiensis is the effect of energy reduction/food availability and quality in regards to populations isolated on islands from parent populations. Floresiensis was able to survive on about 1200 kcal by shrinking, needing to consume about 1400 kcal during lactation compared to 1800 kcal for an erectus female who needed about 2500 kcal during lactation (Lieberman, 2013: 125). The cognitive price for the reduction in the brain size of floresiensis is not known, but since brains are so energy expensive (Aiello and Wheeler, 1995; Herculano-Houzel and Kaas, 2011; Fonseca-Azevedo and Herculano-Houzel, 2012), the reduction seen in floresiensis is no surprise.

Energy is one of the most important drivers for the evolution of a species, the evolution of floresiensis is one major example of this. Whether floresiensis evolved from habilis or erectus, reduced energy on the island caused the brain and body size of floresiensis to get smaller to cope with fewer things to eat. Keep in mind that habilis was a meat-eater as well, and with lower-quality energy on the island, the brain would have to reduce in size as it’s one of the most expensive organs in the body. As I’ve been saying for a long time now, the quality of energy is most important to the evolution of a species—especially Man. Cooking was imperative to our evolution, and with a lower-quality diet, we, too, would evolve smaller brains and bodies to compensate for reduced energy consumption since our brains take 25 percent of our daily energy requirements to power despite being 2 percent of our overall body weight.

The evolution of floresiensis shows how important energy is in the evolution of species. Its biggest implication—no matter if floresiensis evolved from habilis or erectus—is how important diet quality is to evolution, as I’ve noted here, here, here, here, here, and here. Without our high-quality diet, we, too, would suffer the same body/brain size reductions that floresiensis did.

References

Aiello, L. C., & Wheeler, P. (1995). The Expensive-Tissue Hypothesis: The Brain and the Digestive System in Human and Primate Evolution. Current Anthropology,36(2), 199-221. doi:10.1086/204350

Argue, D., Groves, C. P., Lee, M. S., & Jungers, W. L. (2017). The affinities of Homo floresiensis based on phylogenetic analyses of cranial, dental, and postcranial characters. Journal of Human Evolution. doi:10.1016/j.jhevol.2017.02.006

Baab, K. L., Mcnulty, K. P., & Harvati, K. (2013). Homo floresiensis Contextualized: A Geometric Morphometric Comparative Analysis of Fossil and Pathological Human Samples. PLoS ONE,8(7). doi:10.1371/journal.pone.0069119

Baab, K.L. (2016). The place of Homo floresiensis in human evolutionJournal of Anthropological Sciences, 94, 5-18.

Bergh, G. D., Kaifu, Y., Kurniawan, I., Kono, R. T., Brumm, A., Setiyabudi, E., . . . Morwood, M. J. (2016). Homo floresiensis-like fossils from the early Middle Pleistocene of Flores. Nature,534(7606), 245-248. doi:10.1038/nature17999

Bromham, L., & Cardillo, M. (2007). Primates follow the ‘island rule’: implications for interpreting Homo floresiensis. Biology Letters,3(4), 398-400. doi:10.1098/rsbl.2007.0113

Evans AR, Jones D, Boyer AG, Brown JH, Costa DP, et al. (2012) The maximum rate of mammal evolution. Proc Natl Acad Sci USA 109: 4187–4190.

Falk, D., Hildebolt, C., Smith, K., Morwood, M. J., Sutikna, T., Jatmiko, … Prior, F. (2007). Brain shape in human microcephalics and Homo floresiensis. Proceedings of the National Academy of Sciences of the United States of America, 104(7), 2513–2518. http://doi.org/10.1073/pnas.0609185104

Falk, D., Hildebolt, C., Smith, K., Jungers, W., Larson, S., Morwood, M., . . . Prior, F. (2009). The type specimen (LB1) of Homo floresiensis did not have Laron Syndrome. American Journal of Physical Anthropology,140(1), 52-63. doi:10.1002/ajpa.21035

Fonseca-Azevedo, K., & Herculano-Houzel, S. (2012). Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution. Proceedings of the National Academy of Sciences,109(45), 18571-18576. doi:10.1073/pnas.1206390109

Herculano-Houzel, S., & Kaas, J. H. (2011). Gorilla and Orangutan Brains Conform to the Primate Cellular Scaling Rules: Implications for Human Evolution. Brain, Behavior and Evolution, 77(1), 33–44. http://doi.org/10.1159/000322729

Kaifu, Y., Baba, H., Sutikna, T., Morwood, M. J., Kubo, D., Saptomo, E. W., . . . Djubiantono, T. (2011). Craniofacial morphology of Homo floresiensis: Description, taxonomic affinities, and evolutionary implication. Journal of Human Evolution,61(6), 644-682. doi:10.1016/j.jhevol.2011.08.008

Kubo, D., Kono, R. T., & Kaifu, Y. (2013). Brain size of Homo floresiensis and its evolutionary implications. Proceedings of the Royal Society B: Biological Sciences,280(1760), 20130338-20130338. doi:10.1098/rspb.2013.0338

Laron, Z., & Klinger, B. (1994). Laron Syndrome: Clinical Features, Molecular Pathology and Treatment. Hormone Research,42(4-5), 198-202. doi:10.1159/00018419
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Lieberman, D. (2013). The Story of the human body – evolution, health and disease. Penguin.

Mcclain, C. R., Boyer, A. G., & Rosenberg, G. (2006). The island rule and the evolution of body size in the deep sea. Journal of Biogeography,33(9), 1578-1584. doi:10.1111/j.1365-2699.2006.01545.x

Vannucci, R. C., Barron, T. F., & Holloway, R. L. (2011). Craniometric ratios of microcephaly and LB1, Homo floresiensis, using MRI and endocasts. Proceedings of the National Academy of Sciences of the United States of America, 108(34), 14043–14048. http://doi.org/10.1073/pnas.1105585108

Welch, J. J. (2009). Testing the island rule: primates as a case study. Proceedings of the Royal Society B: Biological Sciences,276(1657), 675-682. doi:10.1098/rspb.2008.1180

Weston, E. M., & Lister, A. M. (2009). Insular dwarfism in hippos and a model for brain size reduction in Homo floresiensis. Nature, 459(7243), 85–88. http://doi.org/10.1038/nature07922

Race, Testosterone, and Honor Culture

2300 words

Misinformation about testosterone and strength in regards to race is rampant in the HBD-o-sphere. One of the most oft-repeated phrases is that “Blacks have higher levels of testosterone than whites”, even after controlling for numerous confounds. However, the people who believe this literally only cite one singular study with 50 blacks and 50 whites. Looking at more robust data with higher ns shows a completely different story. Tonight I will, again, go through the race/testosterone conundrum (again).

Type I fibers fire first when heavy lifting. Whites have more type I fibers. Powerlifters and Olympic lifters have a greater amount type IIa fibers, with fewer type IIx fibers (like whites). This explains why blacks are hardly represented in powerlifting and strongman competitions.

Somatype, too, also plays a role. Whites are more endo than blacks who are more meso. Endomorphic individuals are stronger, on average, than mesomorphic and ectomorphic individuals.

Blacks have narrower hips and pelves. This morphological trait further explains why blacks dominate sports. Some people may attempt to pick out one variable that I speak about (fiber type, morphology, somatype, fat mass, etc) and attempt to disprove it, thinking that disproving that variable will discredit my whole argument. However, fiber typing is set by the second trimester, with no change in fiber type from age 6 to adulthood (Bell et al, 1980).

It is commonly believed that blacks have higher levels of testosterone than whites. However, this claim is literally based off of one study (Ross et al, 1986) when other studies have shown low to no difference in T levels (Richards et al, 1992; Gapstur et al, 2002; Rohrmann et al, 2007; Mazur, 2009; Lopez et al, 2013; Richard et al 2014). People who still push the “blacks-have-higher-T-card” in the face of this evidence are, clearly, ideologues who want to cushion their beliefs when presented with contradictory evidence (Nyhan and Reifler, 2010).

‘Honor Culture’ and testosterone

In all of my articles on this subject, I have stated—extensively—that testosterone is mediated by the environment. That is, certain social situations can increase testosterone. This is a viewpoint that I’ve emphatically stated. I came across a paper while back that talks about a sociological perspective (I have huge problems with social ‘science’, [more on that soon] but this study was very well done) in regards to the testosterone difference between blacks and whites.

Some people when they read this, however, may go immediately to the part of the paper that says what they want it to say without fully assessing the paper. In this section, I will explain the paper and how it confirms my assertions/arguments.

Mazur (2016) begins the paper talking about ‘honor culture‘, which is a culture where people avoid intentionally offending others while also maintaining a status for not backing down from a confrontation. This theory was proposed by Richard Nisbett in 1993 to explain why the South had higher rates of violence—particularly the Scotch-Irish.

However parsimonious the theory may sound, despite its outstanding explanatory power, it doesn’t hold while analyzing white male homicides in the South. It also doesn’t hold analyzing within-county homicide rates either, since apparently poverty better explains higher homicide rates.

But let’s assume it’s true for blacks. Let’s assume the contention to be true that there is an ‘honor culture’ that people take part in.

Young black men with no education had higher levels of testosterone than educated whites and blacks. Looking at this at face value—literally going right to the section of the paper that says that poor blacks had higher testosterone, nearly 100 ng/ml higher than the mean testosterone of whites. As Mazur (2016) notes, this contradicts his earlier 2009 study in which he found no difference in testosterone between the races.

fsoc-01-00001-g001

Note the low testosterone for both races at age 20-29—ranging from about 515 to 425—why such low testosterone levels for young men? Anyway, the cause for the higher levels is due to the type of honor culture that blacks participate in, according to Mazur (which is consistent with the data showing that testosterone rises during conflict/aggressive situations).

Mazur cites Elijah Anderson, saying that most youths have a “code of the streets” they take part in, which have to do with interpersonal communication such as “gait and verbal expressions” to deter aggressive behavior.

Testosterone is not a causal variable in regards to violent behavior. But it does rise during conflicts with others, watching a favorite sports team, asserting dominance, and even how you carry yourself (especially your posture). Since low-class blacks participate in these types of behaviors, then they would have higher levels of testosterone due to needing to “keep their status.”

When testosterone rises in these situations, it increases the response threat in mens’ brains, most notably showing increased activity in the amygdala. Further, dominant behavior and posture also increase testosterone levels. Putting this all together, since blacks with only a high school education have higher testosterone levels and are more likely to participate in honor culture compared to whites and blacks with higher educational achievement, then they would have higher testosterone levels than whites and blacks with a high school education who do not participate in honor culture.

Further, as contrary to what I have written in the past (and have since rescinded), there is no indication of higher testosterone levels in black women with low education. It seems this ‘honor culture’ effect on testosterone only holds for black men with only a high school education.

Mazur’s (2016) most significant finding was that black men aged 20-29 with only a high school education had 91 ng/ml higher testosterone than whites. Among older and/or educated men, testosterone did not vary. This indicates that since they have attained higher levels of educational success, there is no need to participate in ‘honor culture’.

This is yet further evidence for my assertion that environmental variables such as posture, dominance, and aggressive behavior raise testosterone levels.

The honor culture hypothesis is found to hold in Brazil in a comparative study of 160 inmates and non-inmates (De Souza et al, 2016). As Mazur (2016) notes, the honor culture hypothesis could explain the high murder rate for black Americans—the need to ‘keep their status’. It’s important to note that this increase in testosterone was not noticed in teenage or female blacks (because they don’t participate in honor culture).

There is a perfectly good environmental—not genetic—reason for this increase in testosterone in young blacks with only a high school education. Now that we know this, back to race and strength.

Mazur (2009) found that black men in the age range of 20-69, they averaged .39 ng/ml higher testosterone than whites, which is partly explained by lower marriage rates and low adiposity. White men are more likely to be obese than black men, since black men with more African ancestry are less likely to be obese. When controlling for BMI, blacks are found to have 2.5-4.9 percent more testosterone than whites (Gapstur et al, 2002, Rohrmann et al, 2007, Richard et al, 2014). There is little evidence for the assertion that blacks have higher levels of testosterone without environmental triggers.

Blacks between the age of 12 and 15 average lower levels of testosterone than whites. However, after the age of 15, “testosterone levels increase rapidly” with blacks having higher peak levels than whites (seen in table 2 below). After adjusting for the usual confounds (BMI, smoking, age, physical activity, and waist circumference), blacks still had higher levels of testosterone—which is attributed to higher levels of lean mass.

testosterone

As seen above in table 2 from Hu et al (2014), the difference in total testosterone between blacks and whites aged 20-39 was 6.29 ng/ml and 5.04 ng/ml respectively, with free testosterone for whites being 11.50 and 13.56 for blacks and finally bioavailable testosterone for whites and blacks aged 20-39 was 281.23 and 327.18 ng/ml respectively. These small differences in testosterone cannot account for racial disparities in violence nor prostate cancer—since there is no relationship between prostate cancer and testosterone (Stattin et al, 2003; Michaud, Billups, and Partin, 2015).

In regards to Africans, the best studies I can find comparing some African countries with the West study salivary testosterone. However, there is a direct correlation between salivary testosterone and free serum testosterone (Wang et al, 1981; Johnson, Joplin, and Burrin, 1987). Of the studies I could find, Kenyan pastoralists called the Ariaal have lower levels of testosterone than Western men (Campbell, O’Rourke, and Lipson, 2003; Campbell, Gray, and Ellison, 2006) while men in Zimbabwe had levels “much lower” compared to Western populations (Lukas, Campbell, and Ellison, 2004). Lastly, among men aged 15 to 30, salivary testosterone levels in an American sample was 335 pmol//l compared to 286 pmol/l in men from the Congo (Elisson et al, 2002). Even certain African populations don’t have higher testosterone levels than Western peoples.

Conclusion

The meme that blacks have higher rates of testosterone in comparison to whites needs to be put to rest. This is only seen in blacks who participate in ‘honor culture’, which is an environmental variable. This is in contrast to people who believe that it is genetic in nature—environmental variables can and do drive hormones. Mazur (2016) is proof of that. Mazur (2016) also shows that the honor culture hypothesis doesn’t hold for teens or black males—so they don’t have elevated levels of testosterone. Certain studies of African populations, however, do not show higher levels of testosterone than Western populations.

Looking at the complete literature—rather than a select few studies— we can see that testosterone levels between white and black Americans are not as high as is commonly stated (Richards et al, 1992; Gapstur et al, 2002; Rohrmann et al, 2007; Mazur, 2009; Lopez et al, 2013; Hu et al, 2014; Richard et al, 2014). Further, even if blacks did have higher levels of testosterone than whites—across the board (sans honor culture), it still wouldn’t explain higher rates of black violence when compared to whites, nor would it explain higher prostate cancer rates (Stattin et al, 2003; Michaud, Billups, and Partin, 2015).

Only blacks with low educational achievement have higher levels of testosterone—which, even then is not enough to explain higher rates of violence or prostate cancer acquisition. Other factors explain the higher murder rate (i.e., honor culture, which increases testosterone, the environmental trigger matters first and foremost) and violent crime that blacks commit. But attempting to explain it with 30-year-old studies (Ross et al, 1986) and studies that show that environmental factors increase testosterone (Mazur, 2016) don’t lend credence to that hypothesis.

References

Bell, R. D., Macdougall, J. D., Billeter, R., & Howald, H. (1980). Muscle fiber types and morphometric analysis of skeletal muscle in six-year-old children. Medicine & Science in Sports & Exercise,12(1). doi:10.1249/00005768-198021000-00007

Campbell, B., O’rourke, M. T., & Lipson, S. F. (2003). Salivary testosterone and body composition among Ariaal males. American Journal of Human Biology,15(5), 697-708. doi:10.1002/ajhb.10203

Campbell, B. C., Gray, P. B., & Ellison, P. T. (2006). Age-related patterns of body composition and salivary testosterone among Ariaal men of Northern Kenya. Aging Clinical and Experimental Research,18(6), 470-476. doi:10.1007/bf03324846

De Souza, Souza, B. C., Bilsky, W., & Roazzi, A. (2016). The culture of honor as the best explanation for the high rates of criminal homicide in Pernambuco: A comparative study with 160 convicts and non-convicts. Anuario de Psicología Jurídica,26(1), 114-121. doi:10.1016/j.apj.2015.03.001

Ellison, P. T., Bribiescas, R. G., Bentley, G. R., Campbell, B. C., Lipson, S. F., Panter-Brick, C., & Hill, K. (2002). Population variation in age-related decline in male salivary testosterone. Human Reproduction,17(12), 3251-3253. doi:10.1093/humrep/17.12.3251

Gapstur SM, Gann PH, Kopp P, Colangelo L, Longcope C, Liu K. Serum androgen concentrations in young men: a longitudinal analysis of associations with age, obesity, and race—the CARDIA male hormone study. Cancer Epidemiol Biomarkers Prev 2002; 11: 10417

Hu, H., Odedina, F. T., Reams, R. R., Lissaker, C. T., & Xu, X. (2014). Racial Differences in Age-Related Variations of Testosterone Levels Among US Males: Potential Implications for Prostate Cancer and Personalized Medication. Journal of Racial and Ethnic Health Disparities,2(1), 69-76. doi:10.1007/s40615-014-0049-8

Johnson, S. G., Joplin, G. F., & Burrin, J. M. (1987). Direct assay for testosterone in saliva: Relationship with a direct serum free testosterone assay. Clinica Chimica Acta,163(3), 309-318. doi:10.1016/0009-8981(87)90249-x

Lopez, D. S., Peskoe, S. B., Joshu, C. E., Dobs, A., Feinleib, M., Kanarek, N., . . . Platz, E. A. (2013). Racial/ethnic differences in serum sex steroid hormone concentrations in US adolescent males. Cancer Causes & Control,24(4), 817-826. doi:10.1007/s10552-013-0154-8

Lukas, W. D., Campbell, B. C., & Ellison, P. T. (2004). Testosterone, aging, and body composition in men from Harare, Zimbabwe. American Journal of Human Biology,16(6), 704-712. doi:10.1002/ajhb.20083

Mazur, A. (2009). The age-testosterone relationship in black, white, and Mexican-American men, and reasons for ethnic differences. The Aging Male,12(2-3), 66-76. doi:10.1080/13685530903071802

Mazur, A. (2016). Testosterone Is High among Young Black Men with Little Education. Frontiers in Sociology,1. doi:10.3389/fsoc.2016.00001

Michaud, J. E., Billups, K. L., & Partin, A. W. (2015). Testosterone and prostate cancer: an evidence-based review of pathogenesis and oncologic risk. Therapeutic Advances in Urology,7(6), 378-387. doi:10.1177/1756287215597633

Nyhan, B., & Reifler, J. (2010). When Corrections Fail: The Persistence of Political Misperceptions. Political Behavior,32(2), 303-330. doi:10.1007/s11109-010-9112-2

Richard, A., Rohrmann, S., Zhang, L., Eichholzer, M., Basaria, S., Selvin, E., . . . Platz, E. A. (2014). Racial variation in sex steroid hormone concentration in black and white men: a meta-analysis. Andrology,2(3), 428-435. doi:10.1111/j.2047-2927.2014.00206.x

Richards, R. J., Svec, F., Bao, W., Srinivasan, S. R., & Berenson, G. S. (1992). Steroid hormones during puberty: racial (black-white) differences in androstenedione and estradiol–the Bogalusa Heart Study. The Journal of Clinical Endocrinology & Metabolism,75(2), 624-631. doi:10.1210/jcem.75.2.1639961

Rohrmann, S., Nelson, W. G., Rifai, N., Brown, T. R., Dobs, A., Kanarek, N., . . . Platz, E. A. (2007). Serum Estrogen, But Not Testosterone, Levels Differ between Black and White Men in a Nationally Representative Sample of Americans. The Journal of Clinical Endocrinology & Metabolism,92(7), 2519-2525. doi:10.1210/jc.2007-0028

Ross R, Bernstein L, Judd H, Hanisch R, Pike M, Henderson B. Serum testosterone levels in healthy young black and white men. J Natl Cancer Inst. 1986 Jan;76(1):45–48

Stattin, P., Lumme, S., Tenkanen, L., Alfthan, H., Jellum, E., Hallmans, G., . . . Hakama, M. (2003). High levels of circulating testosterone are not associated with increased prostate cancer risk: A pooled prospective study. International Journal of Cancer,108(3), 418-424. doi:10.1002/ijc.11572

Wang, C., Plymate, S., Nieschlag, E., & Paulsen, C. A. (1981). Salivary Testosterone in Men: Further Evidence of a Direct Correlation with Free Serum Testosterone. The Journal of Clinical Endocrinology & Metabolism,53(5), 1021-1024. doi:10.1210/jcem-53-5-1021

Evolution Denial Part II

1450 words

Why do people deny evolution? Not just evolution from single-celled organisms to multicellular lifeforms, but human evolution as well? Most people who deny evolution don’t have the knowledge to assess it correctly. They fall back on the Bible and say “God did this, the Bible says…. God says…” all the while looking at you as a heathen when you attempt to talk some basic biology or, God forbid, the process of evolution.

I met a woman the other day and I asked her what she was studying in school. She tells me anatomy and physiology (right up my alley). So we start talking about some basic anatomy and physiology before I ask the question: “Do you believe in evolution?” She gave me a blank stare and said no.

“Humans as we know them have always existed in this form,” she said. I just started laughing at her ignorance and then she said “Evolution at the macro level is not possible but it is at the micro level”, repeating the same old and tired Creationist talking points. I said to her that there is no evidence for creation and that the evidence we do have points to evolution. I said that the theory of evolution has so much backing, so much evidence, that to believe otherwise you’d have to purposefully close your mind to the truth, to shut out any and all contradictory information.

One of the funniest things she said to me was that she wants to cure diseases. To that, I said if she wants to do that then she must look at diseases from an evolutionary perspective (Gluckman et al, 2011). She said that she doesn’t need to know how diseases were in the past, just how they are today. I also said that if she is studying anatomy and physiology then she must understand that many of our appendages are derived from our hominin ancestors, which began with Erectus as I’ve covered in my article Man the AthleteDiseases also must be looked at through an evolutionary lens, so if anyone wants to cure diseases, then they must first understand and accept that things are constantly changing and evolving to better survive in that environment.

When I said that there is no evidence for Creation she got really mad. She said that there is no evidence that “we evolved from monkeys” which gave me a good laugh. Even people who believe in evolution still make that mistake of believing that we evolved from monkeys. One of the most common statements from Creationists is “If humans evolved from monkeys then why are monkeys still around?”, wrongly assuming that we literally evolved from monkeys, incorrectly misinterpreting that we share a common ancestor with monkeys 6-12 mya.

About 6mya, there was a chromosomal fusion on chromosome two; two ancestral ape chromosomes fused to make chromosome two (Idjo et al, 1991). That is some nice chromosomal evidence for common descent from our ape cousins. Creationists, however, purport that a gene in chromosome 2, DDX11L2, writing that the “alleged fusion site is not a degenerate fusion sequence but is and, since creation, has been a functional feature in an important gene.” Further, Tomkins’ claim that the fusion site is actually a gene is wrong since the fusion site is more than 1300 bases away from the gene.

The ancestral equivalents of chromosome 2—2p and 2q—fused together in a fusion event some 6mya. This precise fusion site is on chromosome 2 (Hellier et al, 2004). Creationists will say and do anything to attempt to ‘rebut’ this contention. Genetic evidence is the best evidence we have (due to Punctuated Equilibria, which causes the spottiness in the fossil record), and still, these ‘Creationist geneticists’ will do anything they can to attempt to have Evolutionists go on the defensive. However, the onus is on them to disprove the mountains of evidence.

One of the funniest things this woman said to me is that man has always been in this form and that we didn’t evolve from “monkeys”, which is when I said that it’s more complicated than that: we have fish ancestors, named Tiktaalik who had the beginnings of the human arm and hand, along with Pikaia Gracilens—our oldest ancestor. If Pikaia would have died out in the Cambrian explosion some 550 mya, we wouldn’t be here today. We are here today due to the happenstance of numerous accidents of history—contingencies of “just history” to quote Stephen Jay Gould.

Nevertheless, Creationists will always attempt to distort evolutionary science to fit their agendas. Stephen Jay Gould battled Creationists throughout his career. Creationists would quote mine his books to show that Evolutionists do show evidence of “Creation”. One of his most quote mined works is his and Eldredge’s theory of Punctuated Equilibria (1972). Just because a look at the whole fossil record shows species remaining in stasis for most of their history before a short burst of evolutionary change then that must mean that there was a guiding hand involved in the process. Here is a full list of quote mines that Creationists use from Eldredge and Gould.

As you can see, Creationists use any kind of mental gymnastics to disprove evolution. However, no matter how hard you try with Creationists, you can’t educate people into believing in evolution. This is mainly due to the backfire effect which occurs when you show people contradictory information to a dearly held belief and they frantically attempt to gather evidence to shield themselves from contradictory evidence (Nyhan and Reifler, 2010). This cognitive bias holds for more than political debates, though it’s most often seen there. Showing people any kind of contradictory information will have them search and search for anything to shield themselves from the truth. However, no amount of ‘information’ provided by Creationists will disprove evolutionary theory.

Gould and Eldredge aren’t the only Evolutionist that Creationists quote mine–one of the most famous quote mines is from Darwin’s The Descent of Man in which he talks about defending his theory from detractors, mainly the spottiness of the fossil record (which Eldredge and Gould’s Punctuated Equilibria explains). However, this doesn’t stop Creationists—and even some Evolutionists who fall for Creationist trickery—to believe that Darwin was talking about something completely different, in that Darwin was ‘racist’ talking about the ‘superior races’ exterminating the ‘inferior races’. Reading the quote in its entirety, however, shows something completely different. Alas, some people don’t care about facts antruthut and only care about their agenda they attempt to push.

Even setting evolutionary theory aside, basic geology disproves Creationism. The author of the piece, geologist David Montgomery, says that there is a rock outside of his office that proves Creationism wrong. The rock shows that there is more to the geologic record that could be explained by a single grand flood. Now that geologists now have the tools and data to infer that the earth is billions of years old—not thousands as Young Earth Creationists (YECs) claim—YECs change up their interpretation of the Creation story in Genesis to go from literal days to “days in Genesis refer to geological ages”. Clear mental gymnastics in the face of contradictory evidence.

There are five mass extinctions that are accepted in the scientific community (Jablonski, 2001) (though I am reading a book at the moment that talks about nine mass extinction events with Man pushing the tenth, I will return to this in the future). After these contingencies of ‘just history’, we can see that we are incredibly lucky that our ancestors did not die out. From a Pikaia Gracilens surviving the Cambrian radiation, to Tiktaalik and its venturing onto land from the sea and finally the survival of a shrew-like ancestor during the extinction of the dinosaurs, we should thank our lucky stars that these things went our way, because if not, I wouldn’t be sitting here writing this at the moment and you would not be reading this. Evolutionary history is littered with these events—events that, if they went the other way would not lead to the evolution of Man again.

In sum, people who do not believe in evolutionary theory clearly are emotionally invested in believing in a story of Creation—sans evidence, only their belief. On the other hand, evolutionists such as we have all the data on our side when it comes to this debate. Creationists have to use any kind of warped logic to not believe the mountains of evidence that have piled up since Darwin wrote On the Origin. However, as everyone knows, reality isn’t what just what you believe. Just because Creationists handwave away the data that people like us provide to them doesn’t mean that evolution isn’t true.

 

The Evolution of Human Skin Variation

4050 words

Human skin variation comes down to how much UV radiation a population is exposed to. Over time, this leads to changes in genetic expression. If that new genotype is advantageous in that environment, it will get selected for. To see how human skin variation evolved, we must first look to chimpanzees since they are our closest relative.

The evolution of black skin

Humans and chimps diverged around 6-12 mya. Since we share 99.8 percent of our genome with them, it’s safe to say that when we diverged, we had pale skin and a lot of fur on our bodies (Jablonski and Chaplin, 2000). After we lost the fur on our bodies, we were better able to thermoregulate, which then primed Erectus for running (Liberman, 2015). The advent of fur loss coincides with the appearance of sweat glands in Erectus, which would have been paramount for persistence hunting in the African savanna 1.9 mya, when a modern pelvis—and most likely a modern gluteus maximus—emerged in the fossil record (Lieberman et al, 2006). This sets the stage for one of the most important factors in regards to the ability to persistence hunt—mainly, the evolution of dark skin to protect against high amounts of UV radiation.

After Erectus lost his fur, the unforgiving UV radiation beamed down on him. Selection would have then occurred for darker skin, as darker skin protects against UV radiation. Dark skin in our genus also evolved between 1 and 2 mya. We know this since the melanocortin 1 receptor promoting black skin arose 1-2 mya, right around the time Erectus appeared and lost its fur (Lieberman, 2015).

However, other researchers reject Greaves’ explanation for skin cancer being a driver for skin color (Jablonksi and Chaplin, 2014). They cite Blum (1961) showing that skin cancer is acquired too late in life to have any kind of effect on reproductive success. Skin cancer rates in black Americans are low compared to white Americans in a survey from 1977-8 showing that 30 percent of blacks had basal cell carcinoma while 80 percent of whites did (Moon et al, 1987). This is some good evidence for Greaves’ hypothesis; that blacks have less of a rate of one type of skin cancer shows its adaptive benefits. Black skin evolved due to the need for protection from high levels of UVB radiation and skin cancers.

Highly melanized skin also protects against folate destruction (Jablonksi and Chaplin, 2000). As populations move away from high UV areas, the selective constraint to maintain high levels of folate by blocking high levels of UV is removed, whereas selection for less melanin prevails to allow enough radiation to synthesize vitamin D. Black skin is important near the equator to protect against folate deficiency. (Also see Nina Jablonski’s Ted Talk Skin color is an illusion.)

The evolution of white skin

The evolution of white skin, of course, is much debated as well. Theories range from sexual selection, to diet, to less UV radiation. All three have great explanatory power, and I believe that all of them did drive the evolution of white skin, but with different percentages.

The main driver of white skin is living in colder environments with fewer UV rays. The body needs to synthesize vitamin D, so the only way this would occur in areas with low UV rays.

White skin is a recent trait in humans, appearing only 8kya. A myriad of theories have been proposed to explain this, from sexual selection (Frost, 2007), which include better vitamin D synthesis to ensure more calcium for pregnancy and lactation (which would then benefit the intelligence of the babes) (Jablonski and Chaplin, 2000); others see light skin as the beginnings of more childlike traits such as smoother skin, a higher pitched voice and a more childlike face which would then facilitate less aggressiveness in men and more provisioning (Guthrie, 1970; from Frost, 2007); finally, van den Berghe and Frost (1986) proposed that selection for white skin involved unconscious selection by men for lighter-skinned women which is used “as a measure of hormonal status and thus childbearing potential” (Frost, 2007). The three aforementioned hypotheses have sexual selection for lighter skin as a proximate cause, but the ultimate cause is something completely different.

The hypothesis that white skin evolved to better facilitate vitamin D synthesis to ensure more calcium for pregnancy and lactation makes the most sense. Darker-skinned individuals have a myriad of health problems outside of their ancestral climate, one of which is higher rates of prostate cancer due to lack of vitamin D. If darker skin is a problem in cooler climates with fewer UV rays, then lighter skin, since it ensures better vitamin D synthesis, will be selected for. White skin ensures better and more vitamin D absorption in colder climates with fewer UV rays, therefore, the ultimate cause of the evolution of white skin is a lack of sunlight and therefore fewer UV rays. This is because white skin absorbs more UV rays which is better vitamin D synthesis.

Peter Frost believes that Europeans became white 11,000 years ago. However, as shown above, white skin evolved around 8kya. Further, contrary to popular belief, Europeans did not gain the alleles for white skin from Neanderthals (Beleza et al, 2012). European populations did not lose their dark skin immediately upon entering Europe—and Neanderthal interbreeding didn’t immediately confer the advantageous white skin alleles. There was interbreeding between AMH and Neanderthals (Sankararaman et al, 2014). So if interbreeding with Neanderthals didn’t infer white skin to proto-Europeans, then what did?

A few alleles spreading into Europe that only reached fixation a few thousand years ago. White skin is a relatively recent trait in Man (Beleza et al, 2012). People assume that white skin has been around for a long time, and that Europeans 40,000 ya are the ancestors of Europeans alive today. That, however, is not true. Modern-day European genetic history began about 6,500 ya. That is when the modern-day European phenotype arose—along with white skin.

Furthermore, Eurasians were still a single breeding population 40 kya, and only diverged recently, about 25,000 to 40,000 ya (Tateno et al, 2014). The alleles that code for light skin evolved after the Eurasian divergence. Polymorphisms in the genes ASIP and OCA2 may code for dark and light skin all throughout the world, whereas SLC24A5, MATP, and TYR have a predominant role in the evolution of light skin in Europeans but not East Asians, which suggests recent convergent evolution of a lighter pigmentation phenotype in European and East Asian populations (Norton et al, 2006). Since SLC24A5, MATP, and TYR are absent in East Asian populations, then that means that East Asians evolved light skin through completely different mechanisms than Europeans. So after the divergence of East Asians and Europeans from a single breeding population 25-40kya, there was convergent evolution for light pigmentation in both populations with the same selection pressure (low UV).

Some populations, such as Arctic peoples, don’t have the skin color one would predict they should have based on their ancestral environment. However, their diets are high in shellfish which is high in vitamin D, which means they can afford to remain darker-skinned in low UV areas. UV rays reflect off of the snow and ice in the summer and their dark skin protects them from UV light.

Black-white differences in UV absorption

If white skin evolved to better synthesize vitamin D with fewer (and less intense) UV rays, then those with blacker skin would need to spend a longer time in UV light to synthesize the same amount of vitamin D. Skin pigmentation, however, is negatively correlated with vitamin D synthesis (Libon, Cavalier, and Nikkels, 2013). Black skin is less capable of vitamin D synthesis. Furthermore, blacks’ skin color leads to an evolutionary environmental mismatch. Black skin in low UV areas is correlated with rickets (Holick, 2006), higher rates of prostate cancer due to lower levels of vitamin D (Gupta et al, 2009; vitamin D supplements may also keep low-grade prostate cancer at bay).

Libon, Cavalier, and Nikkels, (2013) looked at a few different phototypes (skin colors) of black and white subjects. The phototypes they looked at were II (n=19), III (n=1), and VI (n-11; whites and blacks respectively). Phototypes are shown in the image below.

skin-type-chart

fitzpatrick-color-chart

To avoid the influence of solar UVB exposure, this study was conducted in February. On day 0, both the black and white subjects were vitamin D deficient. The median levels of vitamin D in the white subjects was 11.9 ng/ml whereas for the black subjects it was 8.6 ng/ml—a non-statistically significant difference. On day two, however, concentrations of vitamin D in the blood rose from 11.9 to 13.3 ng/ml—a statistically significant difference. For the black cohort, however, there was no statistically significant difference in vitamin D levels. On day 6, levels in the white subjects rose from 11.6 to 14.3 ng/ml whereas for the black subjects it was 8.6 to 9.57 ng/ml. At the end of day 6, there was a statistically significant difference in circulating vitamin D levels between the white and black subjects (14.3 ng/ml compared to 9.57 ng/ml).

Different phototypes absorb different amounts of UV rays and, therefore, peoples with different skin color absorb different levels of vitamin D. Lighter-skinned people absorb more UV rays than darker-skinned people, showing that white skin’s primary cause is to synthesize vitamin D.

UVB exposure increases vitamin D production in white skin, but not in black skin. Pigmented skin, on the other hand, hinders the transformation of 7-dehydrocholesterol to vitamin D. This is why blacks have higher rates of prostate cancer—they are outside of their ancestral environment and what comes with being outside of one’s ancestral environment are evolutionary mismatches. We have now spread throughout the world, and people with certain skin colors may not be adapted for their current environment. This is what we see with black Americans as well as white Americans who spend too much time in climes that are not ancestral to them. Nevertheless, different-colored skin does synthesize vitamin D differently, and knowledge of this will increase the quality of life for everyone.

Even the great Darwin wrote about differences in human skin color. He didn’t touch human evolution in On the Origin of Species (Darwin, 1859), but he did in his book Descent of Man (Darwin, 1871). Darwin talks about the effects of climate on skin color and hair, writing:

It was formerly thought that the colour of the skin and the character of the hair were determined by light or heat; and although it can hardly be denied that some effect is thus produced, almost all observers now agree that the effect has been very small, even after exposure during many ages. (Darwin, 1871: 115-116)

Darwin, of course, championed sexual selection as the cause for human skin variation (Darwin, 1871: 241-250). Jared Diamond has the same view, believing that natural selection couldn’t account for hair loss, black skin and white skin weren’t products of natural selection, but female mate preference and sexual selection (Greaves, 2014).

Parental selection for white skin 

Judith Rich Harris, author of the book The Nurture Assumption: Why Kids Turn Out the Way They Do (Harris, 2009), posits another hypothesis for the evolution of light skin for those living in northern latitudes—parental selection. This hypothesis may be controversial to some, as it states that dark skin is not beautiful and that white skin is.

Harris posits that selection for lighter skin was driven by sexual selection, but states that parental selection for lighter skin further helped the fixation of the alleles for white skin in northern populations. Neanderthals were a furry population, as they had no clothes, so, logic dictates that if they didn’t have clothes then they must have had some sort of protection against the cold Ice Age climate, therefore they must have had fur.

Harris states that since lighter skin is seen as more beautiful than darker skin, then if a woman birthed a darker/furrier babe than the mother would have committed infanticide. Women who birth at younger ages are more likely to commit infanticide, as they still have about twenty years to birth a babe. On the other hand, infanticide rates for mothers decrease as she gets older—because it’s harder to have children the older you get.

Harris states that Erectus may have been furry up until 2 mya, however, as I’ve shown, Erectus was furless and had the ability to thermoregulate—something that a hairy hominin was not able to do (Lieberman, 2015).

There is a preference for lighter-skinned females all throughout the world, in Africa (Coetzee et al, 2012); China and India (Naidoo et al, 2016; Dixson et al, 2007); and Latin America and the Philipines (Kiang and Takeuchi, 2009). Light skin is seen as attractive all throughout the world. Thus, since light skin allows better synthesize of vitamin D in colder climes with fewer UV rays, then there would have been a myriad of selective pressures to push that along—parental selection for lighter-skinned babes being one of them. This isn’t talked about often, but infanticide and rape have both driven our evolution (more on both in the future).

Harris’ parental selection hypothesis is plausible, and she does use the right dates for fur loss which coincides with the endurance running of Erectus and how he was able to thermoregulate body heat due to lack of fur and more sweat glands. This is when black skin began to evolve. So with migration into more northerly climes,  lighter-skinned people would have more of an advantage than darker-skinned people. Infanticide is practiced all over the world, and is caused—partly—by a mother’s unconscious preferences.

Skin color and attractiveness

Lighter skin is seen as attractive all throughout the world. College-aged black women find lighter skin more attractive (Stephens and Thomas, 2012). It is no surprise that due to this, a lot of black women lighten their skin with chemicals.

In a sample of black men, lighter-skinned blacks were more likely to perceive discrimination than their darker-skinned counterparts (Uzogara et al, 2014). Further, in appraising skin color’s effect on in-group discrimination, medium-skinned black men perceived less discrimination than lighter- and darker-skinned black men. Lastly—as is the case with most studies—this effect was particularly pronounced for those in lower SES brackets. Speaking of SES, lighter-skinned blacks with higher income had lower blood pressure than darker-skinned blacks with higher income (Sweet et al, 2007). The authors conclude that a variety of psychosocial stress due to discrimination must be part of the reason why darker-skinned blacks with a high SES have worse blood pressure—but I think there is something else at work here. Darker skin on its own is associated with high blood pressure (Mosley et al, 2000). I don’t deny that (perceived) discrimination can and does heighten blood pressure—but the first thing that needs to be looked at is skin color.

Lighter-skinned women are seen as more attractive (Stephen et al, 2009). This is because it signals fertility, femininity, and youth. One more important thing it signals is the ability to carry a healthy child to term since lighter skin in women is associated with better vitamin D synthesis which is important for a growing babe.

Skin color and intelligence

There is a high negative correlation between skin color and intelligence, about –.92 (Templer and Arikawa, 2006). They used the data from Lynn and Vanhanen’s 2002 book IQ and the Wealth of Nations and found that there was an extremely strong negative correlation between skin color and IQ. However, data wasn’t collected for all countries tested and for half of the countries the IQs were ‘estimated’ from other surrounding countries’ IQs.

Jensen (2006) states that the main limitation in the study design of Arikawa and Templer (2006) is that “correlations obtained from this type of analysis are completely non-informative regarding any causal or functional connection between individual differences in skin pigmentation and individual differences in IQ, nor are they informative regarding the causal basis of the correlation, e.g., simple genetic association due to cross-assortative mating for skin color and IQ versus a pleiotropic correlation in which both of the phenotypically distinct but correlated traits are manifested by one and the same gene.”

Lynn (2002) purported to find a correlation of .14 in a representative sample of American blacks (n=430), concluding that the proportion of European genes in African Americans dictates how intelligent that individual black is. However, Hill (2002) showed that when controlling for childhood environmental factors such as SES, the correlation disappears and therefore, a genetic causality cannot be inferred from the data that Lynn (2002) used.

Since Lynn found a .14 correlation between skin color and IQ in black Americans, that means that only .0196 percent of the variation in IQ within black American adults can be explained by skin color. This is hardly anything to look at and keep in mind when thinking about racial differences in IQ.

However, other people have different ideas. Others may say that since animal studies find that lighter animals are less sexually active, are less aggressive, have a larger body mass, and greater stress resistance. So since this is seen in over 40 species of vertebrate, some fish species, and over 30 bird species (Rushton and Templer, 2012) that means that it should be a good predictor for human populations. Except it isn’t.

Razib Khan states:

we know the genetic architecture of pigmentation. that is, we know all the genes (~10, usually less than 6 in pairwise between population comparisons). skin color varies via a small number of large effect trait loci. in contrast, I.Q. varies by a huge number of small effect loci. so logically the correlation is obviously just a correlation. to give you an example, SLC45A2 explains 25-40% of the variance between africans and europeans.

long story short: it’s stupid to keep repeating the correlation between skin color and I.Q. as if it’s a novel genetic story. it’s not. i hope don’t have to keep repeating this for too many years.

Finally, variation in skin color between human populations are primarily due to mutations on the genes MC1RTYRMATP (Graf, Hodgson, and Daal, 2005), and SLC24A5 (also see Lopez and Alonso, 2014 for a review of genes that account for skin color) so human populations aren’t “expected to consistently exhibit the associations between melanin-based coloration and the physiological and behavioural traits reported in our study” (Ducrest, Keller, and Roulin, 2008). Talking about just correlations is useless until causality is established (if it ever is).

Conclusion

The evolution of human skin variation is complex and is driven by more than one variable, but some are stronger than others. The evolution of black skin evolved—in part—due to skin cancer after we lost our fur. White skin evolved due to sexual selection (proximate cause) and to better absorb UV rays for vitamin D synthesis in colder climes (the true need for light skin in cold climates). Eurasians split around 40kya, and after this split both evolved light skin pigmentation independently. As I’ve shown, the alleles that code for skin color between blacks and whites don’t account for differences in aggression, nor do they account for differences in IQ. The genes that control skin color (about a dozen) pale in comparison to the genes that control intelligence (thousands of genes with small effects). Some other hypotheses for the evolution of white skin are on par with being as controversial as the hypothesis that skin color and intelligence co-evolved—mainly that mothers would kill darker-skinned babies because they weren’t seen as beautiful as lighter-skinned babies.

The evolution of human skin variation is extremely interesting with many competing hypotheses, however, to draw wild conclusions based on just correlations in regards to human skin color and intelligence and aggression, you’re going to need more evidence than just correlations.

References

Bang KM, Halder RM, White JE, Sampson CC, Wilson J. 1987. Skin cancer in black Americans: A review of 126 cases. J Natl Med Assoc 79:51–58

Beleza, S., Santos, A. M., Mcevoy, B., Alves, I., Martinho, C., Cameron, E., . . . Rocha, J. (2012). The Timing of Pigmentation Lightening in Europeans. Molecular Biology and Evolution,30(1), 24-35. doi:10.1093/molbev/mss207

Blum, H. F. (1961). Does the Melanin Pigment of Human Skin Have Adaptive Value?: An Essay in Human Ecology and the Evolution of Race. The Quarterly Review of Biology,36(1), 50-63. doi:10.1086/403275

Coetzee V, Faerber SJ, Greeff JM, Lefevre CE, Re DE, et al. (2012) African perceptions of female attractiveness. PLOS ONE 7: e48116.

Darwin, C. (1859). On the origin of species by means of natural selection, or, the preservation of favoured races in the struggle for life. London: J. Murray.

Darwin, C. (1871). The descent of man, and selection in relation to sex. London: John Murray, Albemarle Street.

Dixson, B. J., Dixson, A. F., Li, B., & Anderson, M. (2006). Studies of human physique and sexual attractiveness: Sexual preferences of men and women in China. American Journal of Human Biology,19(1), 88-95. doi:10.1002/ajhb.20584

Ducrest, A., Keller, L., & Roulin, A. (2008). Pleiotropy in the melanocortin system, coloration and behavioural syndromes. Trends in Ecology & Evolution,23(9), 502-510. doi:10.1016/j.tree.2008.06.001

Frost, P. (2007). Human skin-color sexual dimorphism: A test of the sexual selection hypothesis. American Journal of Physical Anthropology,133(1), 779-780. doi:10.1002/ajpa.20555

Graf, J., Hodgson, R., & Daal, A. V. (2005). Single nucleotide polymorphisms in theMATP gene are associated with normal human pigmentation variation. Human Mutation,25(3), 278-284. doi:10.1002/humu.20143

Greaves, M. (2014). Was skin cancer a selective force for black pigmentation in early hominin evolution? Proceedings of the Royal Society B: Biological Sciences,281(1781), 20132955-20132955. doi:10.1098/rspb.2013.2955

Gupta, D., Lammersfeld, C. A., Trukova, K., & Lis, C. G. (2009). Vitamin D and prostate cancer risk: a review of the epidemiological literature. Prostate Cancer and Prostatic Diseases,12(3), 215-226. doi:10.1038/pcan.2009.7

Guthrie RD. 1970. Evolution of human threat display organs. Evol Biol 4:257–302.

Harris, J. R. (2006). Parental selection: A third selection process in the evolution of human hairlessness and skin color. Medical Hypotheses,66(6), 1053-1059. doi:10.1016/j.mehy.2006.01.027

Harris, J. R. (2009). The nurture assumption: why children turn out the way they do. New York: Free Press.

Hill, Mark E. 2002. Skin color and intelligence in African Americans: A reanalysis of Lynn’s data. Population and Environment 24, no. 2:209–14

Holick, M. F. (2006). Resurrection of vitamin D deficiency and rickets. Journal of Clinical Investigation,116(8), 2062-2072. doi:10.1172/jci29449

Jablonski, N. G., & Chaplin, G. (2000). The evolution of human skin coloration. Journal of Human Evolution,39(1), 57-106. doi:10.1006/jhev.2000.0403

Jablonski, N. G., & Chaplin, G. (2014). Skin cancer was not a potent selective force in the evolution of protective pigmentation in early hominins. Proceedings of the Royal Society B: Biological Sciences,281(1789), 20140517-20140517. doi:10.1098/rspb.2014.0517

Jensen, A. R. (2006). Comments on correlations of IQ with skin color and geographic–demographic variables. Intelligence,34(2), 128-131. doi:10.1016/j.intell.2005.04.003

Kiang, L., & Takeuchi, D. T. (2009). Phenotypic Bias and Ethnic Identity in Filipino Americans. Social Science Quarterly,90(2), 428-445. doi:10.1111/j.1540-6237.2009.00625.x

Libon, F., Cavalier, E., & Nikkels, A. (2013). Skin Color Is Relevant to Vitamin D Synthesis. Dermatology,227(3), 250-254. doi:10.1159/000354750

Lieberman, D. E. (2015). Human Locomotion and Heat Loss: An Evolutionary Perspective. Comprehensive Physiology, 99-117. doi:10.1002/cphy.c140011

Lieberman, D. E., Raichlen, D. A., Pontzer, H., Bramble, D. M., & Cutright-Smith, E. (2006). The human gluteus maximus and its role in running. Journal of Experimental Biology,209(11), 2143-2155. doi:10.1242/jeb.02255

López, S., & Alonso, S. (2014). Evolution of Skin Pigmentation Differences in Humans. ELS. doi:10.1002/9780470015902.a0021001.pub2

Lynn, R. (2002). Skin color and intelligence in African Americans. Population and Environment, 23, 365–375.

Mosley, J. D., Appel, L. J., Ashour, Z., Coresh, J., Whelton, P. K., & Ibrahim, M. M. (2000). Relationship Between Skin Color and Blood Pressure in Egyptian Adults : Results From the National Hypertension Project. Hypertension,36(2), 296-302. doi:10.1161/01.hyp.36.2.296

Naidoo, L.; Khoza, N.; Dlova, N.C. A fairer face, a fairer tomorrow? A review of skin lighteners. Cosmetics 2016, 3, 33.

Norton, H. L., Kittles, R. A., Parra, E., Mckeigue, P., Mao, X., Cheng, K., . . . Shriver, M. D. (2006). Genetic Evidence for the Convergent Evolution of Light Skin in Europeans and East Asians. Molecular Biology and Evolution,24(3), 710-722. doi:10.1093/molbev/msl203

Rushton, J. P., & Templer, D. I. (2012). Do pigmentation and the melanocortin system modulate aggression and sexuality in humans as they do in other animals? Personality and Individual Differences,53(1), 4-8. doi:10.1016/j.paid.2012.02.015

Sankararaman, S., Mallick, S., Dannemann, M., Prüfer, K., Kelso, J., Pääbo, S., . . . Reich, D. (2014). The genomic landscape of Neanderthal ancestry in present-day humans. Nature,507(7492), 354-357. doi:10.1038/nature12961

Stephen, I. D., Smith, M. J., Stirrat, M. R., & Perrett, D. I. (2009). Facial Skin Coloration Affects Perceived Health of Human Faces. International Journal of Primatology,30(6), 845-857. doi:10.1007/s10764-009-9380-z

Stephens, D., & Thomas, T. L. (2012). The Influence of Skin Color on Heterosexual Black College Women’s Dating Beliefs. Journal of Feminist Family Therapy,24(4), 291-315. doi:10.1080/08952833.2012.710815

Sweet, E., Mcdade, T. W., Kiefe, C. I., & Liu, K. (2007). Relationships Between Skin Color, Income, and Blood Pressure Among African Americans in the CARDIA Study. American Journal of Public Health,97(12), 2253-2259. doi:10.2105/ajph.2006.088799

Tateno, Y., Komiyama, T., Katoh, T., Munkhbat, B., Oka, A., Haida, Y., . . . Inoko, H. (2014). Divergence of East Asians and Europeans Estimated Using Male- and Female-Specific Genetic Markers. Genome Biology and Evolution,6(3), 466-473. doi:10.1093/gbe/evu027

Templer, D. I., & Arikawa, H. (2006). Temperature, skin color, per capita income, and IQ: An international perspective. Intelligence,34(2), 121-139. doi:10.1016/j.intell.2005.04.002

Uzogara, E. E., Lee, H., Abdou, C. M., & Jackson, J. S. (2014). A comparison of skin tone discrimination among African American men: 1995 and 2003. Psychology of Men & Masculinity, 15(2), 201–212. http://doi.org/10.1037/a0033479

van den Berghe PL, Frost P. 1986. Skin color preference, sexual dimorphism and sexual selection: a case of gene-culture coevolution? Ethn Racial Stud 9:87–113.

Reading Wrongthought Books In Public

750 words.

How many of you have read wrongthought books in public? Books like Race, Evolution, and Behavior, The Blank Slate, The Nurture Assumption, or any other kind of wrongthought literature? I’ve had two specific run-ins this week reading a wrongthought book in public, both people giving me the expected reaction “Why are you reading that?” I bring a few books with me in my daily travels, one of them being Taboo: Why Black Athletes Dominate Sports and Why We’re Afraid To Talk About It.

I was in the bookstore the other day reading Taboo while drinking some coffee and someone came up to me and said, “Why are you reading that?” I responded, “Because I’m interested in the material, why else why I read it?” The person scowled at me and walked away. I don’t understand why you need to ask dumb questions like that. Clearly, if I’m reading something I find an interest in it. People are clearly scared of acknowledging any kind of racial differences in public—even if they cheer for their favorite sports teams a few times a week, not realizing that they’re cheering on people who have inherent genetic advantages due to their morphology. Ironically enough, the book I was reading was talking about how and why blacks dominate sports. That’s ‘racist’ though, so people don’t want to talk about it specifically in public, but they know the truth unconsciously.

As I wrote the other day, people are scared of talking about things that are “natural” in human populations. Because the admission of one population being inherently better, on average than another would then open the gates to talking about other more uncomfortable things, such as racial differences in intelligence. I bet seeing someone read a book like Taboo in public without having knowledge of population differences is pretty jarring for someone who is not privy to the information. However, as we all know, reality isn’t based on how we wish it to be. These taboo subjects that people are scared to approach don’t go away if they don’t acknowledge them.

I had another run-in the other day while drinking some coffee, reading the same wrongthought book. The person asked me “Why are you reading that in public?” with a surprised look on his face. I laughed and said, “Because I can,” and sipped my coffee. People don’t want their preconceived notions challenged (the notion of ‘equality’ of human races). To see someone reading a wrongthought book in public is heresy, and people will always give you an odd look if you’re reading one in public.

I also saw someone reading Outliers by Malcolm Gladwell the other day and I just had to tell them that Gladwell is wrong in his contention that practicing something for 10,000 hours is something that Gladwell has been rebutted on and continues to perpetuate. People should always know there are two sides to every story, whether they want to hear it or not.

People change their minds through reading. So if people who’ve not been exposed to wrongthought books see others reading them, they may be compelled to look into it themselves. That’s the best part about reading those types of books in public. A person may look into it themselves and change their views. I’ve personally found it much easier to change my views on something when I’ve read it myself in comparison to if I’m debating someone.

There is a cognitive bias known as the ‘backfire effect’, where correcting someone actually increases their misperceptions. Engaging people’s beliefs, in the end, just makes them hold onto them more strongly and has them search for evidence to confirm their beliefs. So by people being exposed to wrongthought books they can see them and look into it for themselves and weigh both sides on their own without the possibility of the backfire effect.

So just by exposing others to the covers of these wrongthought books may have them look into something themselves and, possibly, someone else will accept genetic causes for human differences. If you do read a wrongthought book in public and someone attempts to engage you due to what you’re reading, remember the backfire effect. This is why debating people doesn’t change their views because showing people they are wrong (with scholarly sources) has them hold onto their views more strongly. To avoid this, just read a wrongthought book in public so people can see it and look into it themselves.

The “N” Word

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Numerous academics have been looked at as pariahs for uttering this word. This word has a pretty long history offending people. The word I’m talking about is natural. This “N” word—especially today—is extremely divisive in today’s society. If you say that something is ‘natural‘, are you taking away any accomplishments that one has done, all because it’s ‘natural‘?

Take what I’ve been writing about for the past three weeks: athletics. If you say that one is a “natural” at athletic competition, are you taking away the hard work it took for that specific athlete to accomplish his goal? No way. You’re acknowledging that that specific individual has something special that sets him apart from the average person. That’s not to say that hard work, determination, and confidence don’t matter; on the contrary. They DO matter. However, like I said with the Kalenjin Kenyan distance runners (who do have anatomical/physiologic advantages in regards to sprinting): you can take someone with elite genetics who has done elite training and put him up against someone who has subpar genetics (in terms of the athletic event) with elite training—the same training as the athlete with elite genetics—and the athlete with elite genetics/muscle fibers/physiology will constantly blow away the individual who is less genetically gifted.

People readily admit that certain races excel at certain physical activities whereas other races don’t fare as well. As I’ve extensively covered (and provided more than enough evidence/arguments for), the races differ in the number of muscle fibers which cause higher rates of obesity in blacks; this causes strength differences which then correlate with mortality. Finally, somatype is extremely important when speaking about athletics. Blacks have a mesomorphic somatype, which, along with their fiber typing and physiologic differences on average compared to whites, cause blacks to dominate most sporting events. However, when you say that certain races are “naturally more intelligent than others“, people all of a sudden have a bone to pick.

This “N” word when it comes to athletics is perfectly fine to use in our vocabulary, yet when we begin talking about intelligence differences—between races and individuals—all of a sudden we think that everyone is the same and that all brains are made the same. We believe that, although humans evolved genetically isolated for thousands of years and have incurred anatomic/physiologic differences, that one organ—the brain—is somehow exempt from the forces of natural selection. I can think of no traits that WON’T get selected for/against, and so I can think of no reason why the brain wouldn’t be under different selective pressures in Siberia/Northern Europe/the Americas/Africa/PNG/Australia.

However, as far as I can tell, we have not found any alleles that differ between populations. It was proposed in 2005 that the genes ASPM and Microcephalin influenced brain growth (Evans et al, 2005; Mekel-Brobov et al, 2005). However, two years later, Rushton, Vernon and Ann Bons (2007) showed that there was no evidence that Microcephalin and ASPM were associated with general mental ability (GMA), head circumference or altruism. Peter Frost cites Woodley et al, (2014) showing that the correlation between microcephalin and IQ is .79, whereas the correlation with ASPM and IQ was .254. Woodley et al (2014) also show there is a correlation between Disability Adjusted Life Years (DALY) and Microcephalin. The reasoning is that Microcephalin may improve the body’s immune response to viral infections, enabling humans to live in larger societies and thus get selected for higher IQ. Since the allele seems to give better disease resistance, then, over time, selection for higher intelligence can be selected for since fewer people are dying from disease due to increased resistance.

Nevertheless, the debate is still out on this allele. However, the data does look good in that we may have found certain polymorphisms that differ between populations which may explain some racial differences in intelligence. (For more information on IQ alleles, see Race and IQ: the Case for Genes).

Now, we are beginning to have some good evidence pile up showing that there are population differences in these alleles, and that they do predict intelligence. Racial differences in intelligence aren’t accepted by mainstream science and the public at large (obviously) like physiologic/anatomic differences are between human populations. Populations are split for thousands of years. They evolve different anatomy/physiology based on the environment. So, then, why wouldn’t psychological differences appear between the races of Man, when other, physical changes occurred from the OoA migration? It literally makes no sense.

People readily admit that athleticism is largely “natural“, yet when someone says that differences in intelligence are largely due to genes they get shouted down and called a ‘racist’, as if that adds anything to the dialogue. People readily admit that individuals/races are “naturally” leaner/stronger/faster/have quicker reflexes. But if one just even hints at thinking about “natural” differences between populations when it comes to general mental ability, they will be shouted down and their careers will be ruined.

Why? Why are people so scared of the “N” word? Because people want to believe that what they do or do not accomplish comes down to them as an individual and only them. They don’t want to think about the complex interaction between genes x environment and how that shapes an individual’s life path. They only think about environment, and not any possible genetic factors. Certain people—mostly social science majors—deny that evolution had ANY impact on human behavior. The “N” word, especially in today’s society, is a completely divisive word. State that you hold hereditarian views (in terms of mental ability) in regards to differences between populations and athletic events and no one will bat an eye.

“Didn’t you see Usain Bolt blow away the competition and set a new world record in the 100m dash at 9.58 seconds?!”

“He’s naturally good, he was born a gifted athlete.”

No one will bat an eye if you say this. This is where the tables will be flipped if you say:

“Don’t you know that differences in intelligence are largely genetic in nature and no matter how much you ‘train the brain’ you’ll stay at that intelligence level?”

“Man, that’s racist. That shouldn’t be looked at. We are all the same and equal. Except when it comes to certain athletic events, then we are not equal and some populations have natural predispositions that help them win. Evolution stopped at the neck 100kya; the only parts of the body under selective pressure over the past 100kya is below the neck!”

People who say this need to explain exactly what shields the brain from selection pressures. Man originated in Africa, the descendants of the soon-to-be coalesced races spent tens of thousands of years in differing environments. You need to do different things to survive in different environments. Just as the races differ physically, they differ mentally as well. Evolution did not stop at the neck. Significant changes in the brain have occurred in the past 10,000 years. There was a trade-off with agriculture, in that it was responsible for the population explosion which was responsible for mutations that affect intelligence and thus get selected for.

The “N” word is not a scary word. It is, in fact, it’s just common sense. People need to realize that by accepting genetic explanations for black domination in sports, that they would then, logically, have to accept racial differences in intelligence. It makes no sense to accept evolutionary theories (even if you don’t know it) in regards to athletics and not accept the same evolutionary theories for racial differences in the brain. There are real differences between populations, in both anatomy/physiology and our mental faculties and brain organization. If you accept one, you have to accept the other.

Racial Differences in Somatype

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One’s somatype is, really, the first thing they notice. Somatypes are broken down into three categories: ectomorph (skinny build), endomorph (rounder, fatter build) and mesomorph (taller, more muscular build). Like numerous other traits, different races and ethnies fall somewhere in between these three soma categories. Africans are meso, while Europeans are endo, while East Asians are more endo than Europeans. Differences in somatype, too, lead to the expected racial differences in sports due to differing anatomy and fat mass.

History of somatyping

The somatype classification was developed by psychiatrist William Sheldon in the 1940s, while releasing a book in 1954 titled Atlas of Men: Somatotyping the Adult Male At All AgesHe theorized that one’s somatype could predict their behavior, intelligence, and where they place socially. Using nude posture photos from his Ivy League students, he grouped people into three categories based on body measurements and ratios—mesomorph, endomorph, and ectomorph. Clearly, his theory is not backed by modern psychology, but I’m not really interested in that. I’m interested in the somatyping.

Somatypes

The three somatypes are endomorph, mesomorph, and ectomorph. Each type has different leverages and body fat distribution. Endomorphs are rounder, with short limbs, a large trunk, carry more fat in the abdomen and lower body, large chest, wide hips, and has hardly any muscular definition, yet gain strength easily. Ectomorphs, on the other hand, are taller, lankier with longer limbs, a narrow chest, thin body, short trunk and has little muscle.

There are further subdivisions within the three main types, mesomorphic-endomorph (meso-dominant), mesomorph-endomorph (both types are equal with less ectomorphy), ectomorphic-mesomorph, endomorphic-mesomorph, endomorph-ectomorph, and ectomorphic-endomorph. This can be denoted as “7-1-1”, which would indicate pure endomorph, “1-7-1” would indicate pure mesomorph and “1-1-7” would be a pure ectomorph. Further breakdowns can be made such as “1.6-2.7-6.4”, indicating the somatype is ecto-dominant. On the scale, 1 is extremely low while 7 is extremely high. The races, however, fall along racial lines as well.

Racial differences in somatype

West Africans and their descendants are the most mesomorphic. They also have the highest amount of type II muscle fibers which is a leading cause of their success in sporting events which call for short bursts of speed. Due to having longer limbs, they have a longer stride and can generate more speed. West Africans also have the narrowest hips out of all of the races (Rushton, 1997: 163) which further leads to their domination in sprinting competitions and events that take quick bursts of speed and power. However much success their morphology lends them in these types of competitions, their somatype hampers them when it comes to swimming. The first black American qualified for the Olympic swimming team in the year 2000. This is due to a narrower chest cavity and denser, heavier bones.

East Africans are most ectomorphic which you can see by their longer limbs and skinnier body. They have an average BMI of 21.6, one of the lowest in the world. Their low BMI, ectomorphic somatype and abundance of slow twitch muscle fibers are why they dominate in distance running events. Many explanations have been proposed to explain why East Africans (specifically Kenyans and Ethiopians) dominate distance running. The main factor is their somatype (ectomorphic) (Wilbur and Pitsiladis, 2012). The authors, however, downplay other, in my opinion, more important physiologic characteristics such as muscle fiber typing, and differences in physiology. Of course their somatype matters for why they dominate, but other important physiologic characteristics do matter. They clearly evolved together so you cannot separate them.

Europeans are more endo than East Africans and West Africans but less so than East Asians. Europeans have a strong upper body, broad shoulders, longer and thicker trunk and shorter extremities along with 41 percent slow twitch fibers compared to blacks’ 33 percent slow twitch fibers. This is why Europeans dominate power sports such as powerlifting and the World’s Strongest Man. Eighty to 100 percent of the differences in total variation in height, weight, and BMI between East Asians and Europeans are associated with genetic differences (Hur et al, 2008). If the variation between East Asians and Europeans on height, weight and BMI are largely attributed to genetic factors, then the same, I assume, should be true for Africans and Europeans/East Asians.

East Asians are the most endomorphic race and have lighter skeletons and more body fat. They have short arms and legs with a large trunk, which is a benefit when it comes to certain types of lifting movements (such as Olympic lifting, where East Asians shine) but hampers them when it comes to sprinting and distance running (although they have higher rates of type I fibers). East Asians also have more body fat at a lower BMI which is further evidence for the endomorphic somatype. This is also known as ‘TOFI’, ‘Thin on the Outside, Fat on the Inside’. Chinese and Thai children had a higher waist circumference and higher trunk fat deposits than Malay and Lebanese children (Liu et al, 2011). This is a classic description of the endomorphic individual.

Human hands and feet are also affected by climate. Climatic variation played a role in shaping the racial somatic differences we see today. The differences seen in hands and feet “might be due to the presence of evolutionary constraints on the foot to maintain efficient bipedal locomotion” (Betti et al, 2015).

Black-white differences in somatype

Fifty percent of the variability in lean mass is due to genetic factors (Arden and Specter, 1997) with the heritability of stature 85 percent in a meta-analysis (Peeters et al, 2009). Racial differences in somatype are also seen at a young age (Malina, 1969). Blacks had better muscular development and less fat-free mass at an early age. Vickery et al (1988) argued that since blacks have thinner skin folds that caliper measurements testing differences in body fat would be skewed. Malina (1969) also reports the same. Note that Malina’s paper was written in 1969, literally right before it got pushed on the American populace that fat was bad and carbohydrates were good.

Looking at the two tables cited by Malina (1969) on somatype we can see the difference between blacks and whites.

Data from Malina, (1969: 438) n Mesomorph Ectomorph Endomorph
Blacks 65 5.14 2.99 2.92
Whites 199 4.29 2.89 3.86
Data from Malina (1969: 438) Blacks Whites
Thin-build body type 8.93 5.90
Submedium fatty development 48.31 29.39
Medium fleshiness 33.69 43.63
Fat and very fat categories 9.09 21.06

Since this data was collected literally before we went down the wrong path and wrongly demonized fat and (wrongly) championed carbohydrates, this is an outstanding look at somatype/fat mass before the obesity epidemic. There is a clear trend, with blacks being more likely to have lower levels of fat-free body mass while also more likely to be mesomorphic. This has a ton of implications for racial differences in sports.

Somatype is predicated on lean mass, stature, bone density and fat-free body mass. Since racial differences appear in somatype at an early age, there is a great chance that the differences in somatype are genetic in nature.

College (American) football players are more likely to be endo-mesomorphs while high-school football players were more likely to be mesomorphs (Bale et al, 1994). This partly explains black over representation in football. Further, basketball, handball, and soccer players in Nigeria were taller, heavier, and had lower percent body fat than other athletic groups (Mazur, Toriola, and Igobokwe, 1985). Somatic differences have a lot to do with domination in sports competition.

Somatic differences are also seen in boxing. Elite boxers are more likely to have a mesomorphic somatype compared to non-athletes. Higher weight divisions were also more likely to be mesomorphic and endomorphic than the lower weight divisions which skewed ectomorphic (Noh et al, 2014). Blacks do well in boxing since they have a more mesomorphic somatype. Due to their higher levels of type II fibers, they can be quicker and throw more forceful punches which translates to boxing success.

Conclusion

Racial differences in somatype are another key to the puzzle to figure out why the races differ in elite sporting competition. The races evolved in different geographic locations which then led to differences in somatype. West African sports dominance is explained by their somatype, muscle fiber type, and physiology. The same can be said for Europeans in strength sports/powerlifting sports, and East Asians with ping-pong and some strength sports (though, due to lower muscle mass they are the least athletic of the races). I am not, of course, denying the impact of determination to succeed or training of any kind. What one must realize, however, is that one with the right genetic makeup/somatype and elite training will, way more often than not, outperform an individual with the wrong genetic makeup/somatype and elite training. These inherent differences between races explain the disparities in elite sporting competitions.

References

Arden, N. K., & Spector, T. D. (1997). Genetic Influences on Muscle Strength, Lean Body Mass, and Bone Mineral Density: A Twin Study. Journal of Bone and Mineral Research,12(12), 2076-2081. doi:10.1359/jbmr.1997.12.12.2076

Bale P, Colley E, Mayhew JL, et al. Anthropometric and somatotype variables related to strength in American football players. J Sports Med Phys Fitness 1994;34:383–9

Betti, L., Lycett, S. J., Cramon-Taubadel, N. V., & Pearson, O. M. (2015). Are human hands and feet affected by climate? A test of Allen’s rule. American Journal of Physical Anthropology,158(1), 132-140. doi:10.1002/ajpa.22774

Hur, Y., Kaprio, J., Iacono, W. G., Boomsma, D. I., Mcgue, M., Silventoinen, K., . . . Mitchell, K. (2008). Genetic influences on the difference in variability of height, weight and body mass index between Caucasian and East Asian adolescent twins. International Journal of Obesity,32(10), 1455-1467. doi:10.1038/ijo.2008.144

Liu, A., Byrne, N. M., Kagawa, M., Ma, G., Kijboonchoo, K., Nasreddine, L., . . . Hills, A. P. (2011). Ethnic differences in body fat distribution among Asian pre-pubertal children: A cross-sectional multicenter study. BMC Public Health,11(1). doi:10.1186/1471-2458-11-500

Malina, R. M. (1969). Growth and Physical Performance of American Negro and White Children: A Comparative Survey of Differences in Body Size, Proportions and Composition, Skeletal Maturation, and Various Motor Performances. Clinical Pediatrics,8(8), 476-483. doi:10.1177/000992286900800812

Mathur, D. N., Toriola, A. L., & Igbokwe, N. U. (1985). Somatotypes of Nigerian athletes of several sports. British Journal of Sports Medicine,19(4), 219-220. doi:10.1136/bjsm.19.4.219

Noh, J., Kim, J., Kim, M., Lee, J., Lee, L., Park, B., . . . Kim, J. (2014). Somatotype Analysis of Elite Boxing Athletes Compared with Nonathletes for Sports Physiotherapy. Journal of Physical Therapy Science,26(8), 1231-1235. doi:10.1589/jpts.26.1231

Peeters, M., Thomis, M., Beunen, G., & Malina, R. (2009). Genetics and Sports: An Overview of the Pre-Molecular Biology Era. Genetics and Sports Medicine and Sport Science, 28-42. doi:10.1159/000235695

Rushton J P (1997). Race, Evolution, and Behavior. A Life History Perspective (Transaction, New Brunswick, London).

Vickery SR, Cureton KJ, Collins MA. Prediction of body density from skinfolds in black and white young men. Hum Biol 1988;60:135–49.

Wilber, R. L., & Pitsiladis, Y. P. (2012). Kenyan and Ethiopian Distance Runners: What Makes Them so Good? International Journal of Sports Physiology and Performance,7(2), 92-102. doi:10.1123/ijspp.7.2.92

Possibly Retracting My Article on HBD and Baseball

700 words

I am currently reading Taboo: Why Black Athletes Dominate Sports and Why We’re Afraid To Talk About It and came across a small section in the beginning of the book talking about black-white differences in baseball. It appears I am horribly, horribly wrong and it looks like I may need to retract my article HBD and Sports: Baseball. However, I don’t take second-hand accounts as gospel, so I will be purchasing the book that Entine cites, The Bill James Baseball Abstract 1987 to look into it myself and I may even do my own analysis on modern-day players to see if this still holds. Nevertheless, at the moment disregard the article I wrote last year until I look into this myself.


Excerpt from Taboo: Why Black Athletes Dominate Sports and Why We’re Afraid To Talk About It:

Baseball historian Bill James, author of dozens of books on the statistical twists of his favorite sport believes this trend [black domination in baseball] is not a fluke. In an intriguing study conducted in 1987, he compared the careers of hundreds of rookies to figure out what qualities best predict who would develop into stars. He noted many intangible factors, such as whether a player stays fit or is just plain lucky. The best predictors of long-term career success included the age of the rookie, his defensive position as a determinant in future hitting success (e.g., catchers fare worse than outfielders), speed, and the quality of the player’s team. But all of these factors paled when compared to the color of the player’s skin.

“Nobody likes to write about race,” James noted apologetically. “I thought I would do a [statistical] run of black players against white players, fully expecting that it would show nothing in particular or nothing beyond the outside range of chance, and I would file it away and never mention that I had looked at the issue at all.

James first compared fifty-four white rookies against the same number of black first-year players who had comparable statistics. “The results were astonishing,” James wrote. The black players:

* went on to have better major-league careers in 44 out of 54 cases

* played 48 percent more games

* had 66 percent more major league hits

* hit 93 percent more triples

* hit 66 percent more home runs

* scored 69 percent more runs

* stole 400 more bases (Entine, 2000: 22-23)

Flabbergasted at what he found, James ran a second study using forty-nine black/white comparisons. Again, blacks proved more durable, retained their speed longer, and were consistently better hitters. For example, he compared Ernie Banks, a power hitting shortstop for the Chicago Cubs, and Bernie Allen who broke in with Minnesota. They both reached the majors when they were twenty-three years old, were the same height and weight, and were considered equally fast. Over time, Allen bombed and Banks landed in the Hall of Fame. (Entine, 2000: 24)

In an attempt to correct for possible bias, James compared players with comparable speed statistics such as the number of doubles, triples, and stolen bases. He ran a study focused on players who had little speed. He analyzed for “position bias” and made sure that players in the same eras were being compared. Yet every time he crunched the numbers, the results broke down across racial lines. When comparing home runs, runs scored, RBIs or stolen bases, black players held an advantage a startling 80 percent of the time. “And I could identify absolutely no bias to help explain why this should happen,” James said in disbelief.

James also compared white Hispanic rookies whom he assumed faced an uphill battle similar to that for blacks, with comparable groups of white and black players. The blacks dominated the white Latinos by even more than they did white North Americans, besting them in 19 of the 26 comparisons. Blacks played 62 percent more games, hit 192 more home runs, drove in 125 percent more runs, and stole 30 percent more bases.

So why have blacks become the stars of baseball far out of proportion to their relative numbers? James eventually concluded that there were two possible explanations: “Blacks are better athletes because they are born better athletes, which is to say that it is genetic, or that they are born equal and become better athletes. (Entine, 2000: 24-25)

Black-White Differences in Muscle Fiber and Its Role In Disease and Obesity

1700 words

How do whites and blacks differ by muscle fiber and what does it mean for certain health outcomes? This is something I’ve touched on in the past, albeit briefly, and decided to go in depth on it today. The characteristics of skeletal muscle fibers dictate whether one has a higher or lower chance of being affected by cardiometabolic disease/cancer. Those with more type I fibers have less of a chance of acquiring diabetes while those with type II fibers have a higher chance of acquiring debilitating diseases. This has direct implications for health disparities between the two races.

Muscle fiber typing by race

Racial differences in muscle fiber typing explain differences in strength and mortality. I have, without a shadow of a doubt, proven this. So since blacks have higher rates of type II fibers while whites have higher rates of type I fibers (41 percent type I for white Americans, 33 percent type I for black Americans, Ama et al, 1985) while West Africans have 75 percent fast twitch and East Africans have 25 percent fast twitch (Hobchachka, 1988). Further, East and West Africans differ in typing composition, 75 percent fast for WAs and 25 percent fast for EAs, which has to do with what type of environment they evolved in (Hochhachka, 1998). What Hochhachka (1998) also shows is that high latitude populations (Quechua, Aymara, Sherpa, Tibetan and Kenyan) “show numerous similarities in physiological hypoxia defence mechanisms.” Clearly, slow-twitch fibers co-evolved here.

Clearly, slow-twitch fibers co-evolved with hypoxia. Since hypoxia is the deficiency in the amount of oxygen that reaches the tissues, populations in higher elevations will evolve hypoxia defense mechanisms, and with it, the ability to use the oxygen they do get more efficiently. This plays a critical role in the fiber typing of these populations. Since they can use oxygen more efficiently, they then can become more efficient runners. Of course, these populations have evolved to be great distance runners and their morphology followed suit.

Caesar and Henry (2015) also show that whites have more type I fibers than blacks who have more type II fibers. When coupled with physical inactivity, this causes higher rates of cancer and cardiometabolic disease. Indeed, blacks have higher rates of cancer and mortality than whites (American Cancer Society, 2016), both of which are due, in part, to muscle fiber typing. This could explain a lot of the variation in disease acquisition in America between blacks and whites. Physiologic differences between the races clearly need to be better studied. But we first must acknowledge physical differences between the races.

Disease and muscle fiber typing

Now that we know the distribution of fiber types by race, we need to see what type of evidence there is that differing muscle fiber typing causes differences in disease acquisition.

Those with fast twitch fibers are more likely to acquire type II diabetes and COPD (Hagiwara, 2013); cardiometabolic disease and cancer (Caesar and Henry, 2015); a higher risk of cardiovascular events (Andersen et al, 2015, Hernelahti et al, 2006); high blood pressure, high heart rate, and unfavorable left ventricle geometry leading to higher heart disease rates and obesity (Karjalainen et al, 2006) etc. Knowing what we know about muscle fiber typing and its role in disease, it makes sense that we should take this knowledge and acknowledge physical racial differences. However, once that is done then we would need to acknowledge more uncomfortable truths, such as the black-white IQ gap.

One hypothesis for why fast twitch fibers are correlated with higher disease acquisition is as follows: fast twitch fibers fire faster, so due to mechanical stress from rapid and forceful contraction, this leads the fibers to be more susceptible to damage and thus the individual will have higher rates of disease. Once this simple physiologic fact is acknowledged by the general public, better measures can be taken for disease prevention.

Due to differences in fiber typing, both whites and blacks must do differing types of cardio to stay healthy. Due to whites’ abundance of slow twitch fibers, aerobic training is best (not too intense). However, on the other hand, due to blacks’ abundance of fast twitch fibers, they should do more anaerobic type exercises to attempt to mitigate the diseases that they are more susceptible due to their fiber typing.

Black men with more type II fibers and less type I fibers are more likely to be obese than ‘Caucasian‘ men are to be obese (Tanner et al, 2001). More amazingly, Tanner et al showed that there was a positive correlation (.72) between weight loss and percentage of type I fibers in obese patients. This has important implications for African-American obesity rates, as they are the most obese ethny in America (Ogden et al, 2016) and have higher rates of metabolic syndrome (a lot of the variation in obesity does come down food insecurity, however). Leaner subjects had higher proportions of type I fibers compared to type II. Blacks have a lower amount of type I fibers compared to whites without adiposity even being taken into account. Not surprisingly, when the amount of type I fibers was compared by ethnicity, there was a “significant interaction” with ethnicity and obesity status when type I fibers were compared (Tanner et al, 2001). Since we know that blacks have a lower amount of type I fibers, they are more likely to be obese.

In Tanner et al’s sample, both lean blacks and whites had a similar amount of type I fibers, whereas the lean blacks possessed more type I fibers than the obese black sample. Just like there was a “significant interaction” between ethnicity, obesity, and type I fibers, the same was found for type IIb fibers (which, as I’ve covered, black Americans have more of these fibers). There was, again, no difference between lean black and whites in terms of type I fibers. However, there was a difference in type IIb fibers when obese blacks and lean blacks were compared, with obese blacks having more IIb fibers. Obese whites also had more type IIb fibers than lean whites. Put simply (and I know people here don’t want to hear this), it is easier for people with type I fibers to lose weight than those with type II fibers. This data is some of the best out there showing the relationship between muscle fiber typing and obesity—and it also has great explanatory power for black American obesity rates.

Conclusion

Muscle fiber differences between blacks and whites explain disease acquisition rates, mortality rates (Araujo et al, 2010), and differences in elite sporting competition between the races. I’ve proven that whites are stronger than blacks based on the available scientific data/strength competitions (click here for an in-depth discussion). One of the most surprising things that muscle fibers dictate is weight loss/obesity acquisition. Clearly, we need to acknowledge these differences and have differing physical activity protocols for each racial group based on their muscle fiber typing. However, I can’t help but think about the correlation between strength and mortality now. This obesity/fiber type study puts it into a whole new perspective. Those with type I fibers are more likely to be physically stronger, which is a cardioprotectant, which then protects against all-cause mortality in men (Ruiz et al, 2008; Volaklis, Halle, and Meisenger, 2015). So the fact that black Americans have a lower life expectancy as well as lower physical strength and more tpe II fibers than type I fibers shows why blacks are more obese, why blacks are not represented in strength competitions, and why blacks have higher rates of disease than other populations.The study by Tanner et al (2001) shows that there obese people are more likely to have type II fibers, no matter the race. Since we know that blacks have more type II fibers on average, this explains a part of the variance in the black American obesity rates and further disease acquisition/mortality.

The study by Tanner et al (2001) shows that there obese people are more likely to have type II fibers, no matter the race. Since we know that blacks have more type II fibers on average, this explains a part of the variance in the black American obesity rates and further disease acquisition/mortality.

Differences in muscle fiber typing do not explain all of the variance in disease acquisition/strength differences, however, understanding what the differing fiber typings do, metabolically speaking, along with how they affect disease acquisition will only lead to higher qualities of life for everyone involved.

References

Araujo, A. B., Chiu, G. R., Kupelian, V., Hall, S. A., Williams, R. E., Clark, R. V., & Mckinlay, J. B. (2010). Lean mass, muscle strength, and physical function in a diverse population of men: a population-based cross-sectional study. BMC Public Health,10(1). doi:10.1186/1471-2458-10-508

Andersen K, Lind L, Ingelsson E, Amlov J, Byberg L, Miachelsson K, Sundstrom J. Skeletal muscle morphology and risk of cardiovascular disease in elderly men. Eur J Prev Cardiol 2013.

Ama PFM, Simoneau JA, Boulay MR, Serresse Q Thériault G, Bouchard C. Skeletal muscle characteristics in sedentary Black and Caucasian males. J Appl Physiol 1986: 6l:1758-1761.

American Cancer Society. Cancer Facts & Figures for African Americans 2016-2018. Atlanta: American Cancer Society, 2016.

Ceaser, T., & Hunter, G. (2015). Black and White Race Differences in Aerobic Capacity, Muscle Fiber Type, and Their Influence on Metabolic Processes. Sports Medicine,45(5), 615-623. doi:10.1007/s40279-015-0318-7

Hagiwara N. Muscle fibre types: their role in health, disease and as therapeutic targets. OA Biology 2013 Nov 01;1(1):2.

Hernelahti, M., Tikkanen, H. O., Karjalainen, J., & Kujala, U. M. (2005). Muscle Fiber-Type Distribution as a Predictor of Blood Pressure: A 19-Year Follow-Up Study. Hypertension,45(5), 1019-1023. doi:10.1161/01.hyp.0000165023.09921.34

Hochachka, P.W. (1998) Mechanism and evolution of hypoxia-tolerance in humans. J. Exp. Biol. 201, 1243–1254

Karjalainen, J., Tikkanen, H., Hernelahti, M., & Kujala, U. M. (2006). Muscle fiber-type distribution predicts weight gain and unfavorable left ventricular geometry: a 19 year follow-up study. BMC Cardiovascular Disorders,6(1). doi:10.1186/1471-2261-6-2

Ogden C. L., Carroll, M. D., Lawman, H. G., Fryar, C. D., Kruszon-Moran, D., Kit, B.K., & Flegal K. M. (2016). Trends in obesity prevalence among children and adolescents in the United States, 1988-1994 through 2013-2014. JAMA, 315(21), 2292-2299.

Ruiz, J. R., Sui, X., Lobelo, F., Morrow, J. R., Jackson, A. W., Sjostrom, M., & Blair, S. N. (2008). Association between muscular strength and mortality in men: prospective cohort study. Bmj,337(Jul01 2). doi:10.1136/bmj.a439

Tanner, C. J., Barakat, H. A., Dohm, G. L., Pories, W. J., Macdonald, K. G., Cunningham, P. R., . . . Houmard, J. A. (2001). Muscle fiber type is associated with obesity and weight loss. American Journal of Physiology – Endocrinology And Metabolism,282(6). doi:10.1152/ajpendo.00416.2001

Volaklis, K. A., Halle, M., & Meisinger, C. (2015). Muscular strength as a strong predictor of mortality: A narrative review. European Journal of Internal Medicine,26(5), 303-310. doi:10.1016/j.ejim.2015.04.013