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Humans are adapted to numerous ecosystems on earth. This is only possible due to how our physiological systems interact with the environment in a homeodynamic way. This allowed us to spread across the globe, far away from our ancestral home of Africa, and thusly certain adaptations evolved in those populations—which was driven by our intelligent physiology. I will touch on human cold and hot adaptations, how physiology adapts to the two climates and what this means for the populations that make up Mankind.
Physiological adaptations to Arctic climates
The human body is one of the most amazing and complex biological systems on earth. The human body lives and dies on its physiology and how it can adapt to novel environments. When Man first trekked out of Africa into novel environments, our physiology adapted so we could survive in novel conditions. Over time, our phenotypes adapted to our new climates and humans began looking different from one another due to the climatic differences in their environments.
There is a large body of work on human cold adaptation. Thermal balance in humans is maintained by “vasodilation/vasoconstriction of the skin and peripheral tissues within the so-called thermo-neutral zone” (Daanen and Lichtenbelt, 2016). Two other adaptations occur in the cold: shivering thermogenesis (ST) and non-shivering thermogenesis (NST) and one in the heat (the evaporation of sweat). Humans are not Arctic animals by nature, so, therefore, venturing into novel environments would incur new physiological adaptations to better deal with the cold.
Heat is induced by the body in cold climates by shivering (Tikuisis, Bell, and Jacobs, 1991; Daanen and Lichtenbelt, 2016). So, therefore, people in colder climates will have higher metabolisms than people in tropical environments, to generate more body heat for vital functioning. People living in Arctic environments have fewer sweat glands than people who live in the tropics. Sweating removes heat from the body, so having more sweat glands in colder climates would not be conducive for survival.
People who evolved in Arctic climates would also be shorter and have wider pelves than people who evolved in the tropics. This is seen in Neanderthals and is an example of Cold adaptations also show up in the Greenlandic Inuit due to extinct hominins like the Denisova (Fumagalli et al, 2015).
We can see natural selection at work in the Inuits, due to adaptation to Arctic climates (Galloway, Young, and Bjerregaard, 2012; Cardona et al, 2014; Ford, McDowell, and Pierce, 2015; NIH, 2015; Harper, 2015; Tishkoff, 2015). Climate change is troubling to some researchers, with many researchers suggesting that global warming will have negative effects on the health and food security of the Inuit (WHO, 2003; Furgal and Seguin, 2006; Wesche, 2010; Ford, 2009, 2012; Ford et al, 2014, 2016; McClymont and Myers, 2012; Petrasek, 2014; Petrasek et al, 2015; Rosol, Powell-Hellyer, and Chan, 2016). This Inuit are the perfect people to look to to see how humans adapt to novel climates—especially colder ones. They have higher BMIs which is better for heat retention, and larger brains with wider pelves and a shorter stature.
Metabolic adaptations also occur due to BMI, which would occur due to diet and body composition. Daanen and Lichtenbelt, (2016) write:
Bakker et al.,48 however, showed that Asians living in Europe had lower BAT prevalence and exhibited a poorer shivering and non-shivering response to cold than Caucasians of similar age and BMI. On the other hand, subjects living in polar regions have higher BMI, and likely more white fat for body energy reserves and insulation.49 This cannot be explained by less exercise,50 but by body composition51 and food intake.49
Basal metabolic rate (BMR) also varies by race. Resting metabolic rate is 5% higher in white women when compared to black women (Sharp et al, 2002). Though low cardiovascular fitness explains 25 percent of the variance in RMR differences between black and white women (Shook et al, 2014). People in Arctic regions have a 3-19 higher BMR than predicted on the basis of the polar climates they lived in (Daanen and Lichtenbelt, 2016). Further, whites had a higher BMR than Asians living in Europe. Nigerian men were seen to have a lower BMR than African-American men (Sharp et al, 2002). So, whites in circumpolar locales have a higher BMR than peoples who live closer to the equator. This has to do with physiologic and metabolic adaptations.
Blacks also show slower and lower cold induced vasodilation (CIVD) than whites. A quicker CIVD in polar climates would be a lifesaver.
However, just our physiologic mechanisms alone aren’t enough to weather the cold. Our ingenuity when it comes to making clothes, fire, and finding and hunting for food are arguably more important than our bodies physiologic ability to adapt to its present environment. Our behavioral plasticity (ability to change our behavior to better survive in the environment) was also another major factor in our adaptation to the cold. Then, cultural changes would lead to genetic changes, and those cultural changes—which were due to the cold climates—would then lead to more genetic change and be an indirect effect of the climate. The same, obviously, holds for everywhere in the world that Man finds himself in.
Physiologic changes to tropical climates
Physiologic changes in tropical climates are very important to us as humans. We needed to be endurance runners millions of years ago, and so our bodies became adapted for that way of life through numerous musculoskeletal and physiologic changes (Lieberman, 2015). One of the most important is sweating.
Sweating is how our body cools itself and maintains its body temperature. When the skin becomes too hot, your brain, through the hypothalamus, reacts by releasing sweat through tens of millions of eccrine glands. As I have covered in my article on the evolution of human skin variation, our loss of fur (Harris, 2009) in our evolutionary history made it possible for sweat to eventually cool our body. Improved sweating ability then led to higher melanin content and selection against fur. Another hypothesis is that when we became bipedal, our bodies were exposed to less solar radiation, selecting against the need for fur. Yet another hypothesis is that trekking/endurance running led to selection for furlessness, selecting for sweating and more eccrine glands (Lieberman, 2015).
Anatomic changes include long and thin bodies with longer limbs as heat dissipation is more efficient. People who live in tropical environments have longer limbs than people who live in polar environments. These tall and slender bodies are what is useful in that environment. People with long, slender bodies are disadvantaged in the cold. Further, longer, slender bodies are better for endurance running and sprinting. They also have narrower hips which helps with heat dissipation and running—which means they would have smaller heads than people in more northerly climes. Most adaptations and traits were once useful in whichever environment that organism evolved in tens of thousands of years ago. And certain adaptations from our evolutionary past are still evident today.
Since tropical people have lower BMRs than people at more northerly climes, this could also explain why, for instance, black American women, have higher rates of obesity than women of other races. They have a lower BMR and are sedentary and eat lower-quality food so food insecurity would have more of an effect on that certain phenotype. Africans wouldn’t have fast metabolisms since a faster metabolism would generate more heat.
Physiologic changes due to altitude
The last adaptation I will talk about is how our bodies can adapt to high altitudes and how it’s beneficial. Many human populations have adapted to the chronic hypoxia of high latitudes (Bigham and Les, 2014) which, of course, has a genetic basis. Adaptation to high altitudes also occurred due to the introgression of extinct hominin genes into modern humans.
Furthermore, people in the Andean mountains, people living in the highlands of Kenya and people living on the Tibetan plateau have shown that the three populations adapted to the same stress through different manners. Andeans, for instance, breathe the same way as people in lower latitudes but their red blood cells carry more oxygen per cell, which protects them from the effects of hypoxia. They also have higher amounts of hemoglobin in their blood in comparison to people who live at sea level, which also aids in counterbalancing hypoxia.
Tibetans, on the other hand, instead of having hematological adaptations, they have respiratory adaptations. Tibetans also have another adaptation which expands their blood vessels, allowing the whole body to deliver oxygen more efficiently to different parts. Further, Ethiopians don’t have higher hemoglobin counts than people who live at sea level, so “Right now we have no clue how they do it [live in high altitudes without hematologic differences in comparison to people who live at sea level]”.
Though Kenyans do have genetic adaptations to live in the highlands (Scheinfeldt et al, 2012). These genetic adaptations have arisen independently in Kenyan highlanders. The selective force, of course, is hypoxia—the same selective force that caused these physiologic changes in Andeans and Tibetans.
The human body is amazing. It can adapt both physiologically and physically to the environment and in turn heighten prospects for survival in most any environment on earth. These physiologic changes, of course, have followed us into the modern day and have health implications for the populations that possess these changes. Inuits, for instance, are cold-adapted while the climate is changing (which it constantly does). So, over time, when the ice caps do melt the Arctic peoples will be facing a crisis since they are adapted to a certain climate and diet.
People in colder climates need shorter bodies, higher body fat, lower limb ratio, larger brains etc to better survive in the cold. A whole slew of physiologic processes aids in peoples’ survival in the Arctic, but our ability to make clothes, houses, and fire, in conjunction with our physiological dynamicness, is why we have survived in colder climates. Tropical people need long, slender bodies to better dissipate heat, sweat and run. People who evolved in higher altitudes also have hematologic and respiratory adaptations to better deal with hypoxia and less oxygen due to living at higher elevations.
These adaptations have affected us physiologically, and genetically, which leads to changes to our phenotype and are, therefore, the cause of how and why we look different today. Human biological diversity is grand, and there are a wide variety of adaptations to differing climates. The study of these differences is what makes the study of Man and the genotypic/phenotypic diversity we have is one of the most interesting sciences we have today, in my opinion. We are learning what shaped each population through their evolutionary history and how and why certain physical and physiologic adaptations occurred.
The relationship between exercise and cognitive ability is important, but often not spoken about. Exercise releases many endorphins (Harber and Sutton, 1984) that help to further positive mood, have one better handle stress since sensitivity to stress is reduced after exercise; and after exercise, depression, and anxiety also decrease (Salmon, 2001). Clearly, if you’re attempting to maximize your cognition, you want to exercise. However, a majority of Americans don’t exercise (49 percent of Americans over the age of 18 do aerobic exercise whereas only 20 percent of Americans do both aerobic and muscle-strengthening exercise). The fact that we do not exercise as a country is proof enough that our life expectancy is declining (Olshansky et al, 2005), and we need to exercise—as a country—to reverse the trend.
Regular readers may know of my coverage of obesity on this blog. Understandably, a super majority of people will disregard my views on obesity and its causes as ‘pseudoscience’ or ‘SJW-ness’, that however says nothing to the data (and if anyone would like to discuss this, they can comment on the relevant articles). Since the average American hardly gets any exercise, this can lead to a decrease in cognitive functioning as less blood flows to the brain. Thus, everyone—especially the obese—needs to exercise to reach maximum genetic brain performance, lest they degenerate in cognitive function due a low-quality diet, such as a diet high in n-6 (the SAD diet), which is correlated with decreased cognition. Further, contrary to popular belief, the obese have lower IQs since around age three; obesity does not itself lower genotypic IQ, their IQ is ALREADY LOW which leads to obesity later in life due to a non-ability to delay gratification. Clearly, exercise education needs to be targeted at those with lower IQs since they have a higher chance of becoming obese in comparison to those with lower IQs (Kanazawa, 2013; 2014).
Clearly not eating well and not exercising can have negative effects on cognition. But what are the positives?
As mentioned previously, exercise releases endorphins that cause good mood and block pain. However, the importance of exercise does not stop there. Exercise also leads to faster reaction times on memory tasks and “increased levels of high-arousal positive affect (HAP) and decreased levels of low-arousal positive affect (LAP).” Exercise has important effects on people of all age groups (Hogan, Mata and Carstensen, 2013; Chodzko-Zajko et al, 2009). Further, physical exercise protects against age-related diseases and cognitive decline in the elderly by modifying “metabolic, structural, and functional dimensions of the brain that preserve cognitive performance in older adults.” (Kirk-Sanchez and McGough, 2014). Exercise is, clearly, a brain protectant during both adolsence and old age, so no matter your age if you want a high QoL living the best life possible, you need to supplement an already healthy lifestyle with strength training/cardio (of course, under doctor’s supervision).
Another important benefit to exercise is that it increases blood flow to the brain (Querido and Steele, 2007; Willie and Ainslie, 2011); however, changes in cerebral blood flow (CBF) during exercise are not associated with higher cognition (Ogoh et al, 2014). During prolonged exercise, cognition was improved when blood flow to the middle cerebral artery (MCA) was decreased. Thusly, exercise-induced changes in CBF do not preserve cognitive performance. Exercise to get blood to the brain is imperative for proper brain functioning. Our brains are vampiric, so we need to ‘feed it’ with blood and what’s the best way to ‘feed’ the brain in this context? Exercise!
Exercise also protects against cognitive degeneration in the elderly (Bherer, Erikson and Lie-Ambrose, 2013; Carvalho et al, 2014; Paillard, 2015). Further, longitudinal studies show an association between exercise and a decrease in dementia (Blondell, Hammersley-Mather and Veerman, 2014). The evidence is currently piling up showing that exercise at all ages is good cognitively, reduces mortality as well as a whole slew of other age-related cognitive diseases. The positive benefits of exercise need to be shown to elderly populations since exercise—mainly strength training—reduces the chance of osteoporosis (Layne and Nelson, 1999; Gray, Brezzo, and Fort, 2013). Moreover, elderly people who exercise live longer (Gremeaux et al, 2012). Now, if you don’t exercise, now’s looking like a pretty good time to start, right?
Finally, lack of exercise causes a myriad of deleterious diseases (Booth, Roberts, and Laye, 2014). This is due, in large part to our evolutionary novel environment (Kanazawa, 2004) which leads to evolutionary mismatches. An evolutionary mismatch, in this instance, is our obesogenic environment (Lake and Townshend, 2006). In terms of our current environment, it is evolutionary novel in comparison to our ancestral land (the Savanna; re: Kanazawa, 2004). Modern-day society is ‘evolutionarily novel’. In this case, we haven’t fully adapted (genetically) to our new lifestyles as, Gould said in Full House, our rate of cultural change has vastly exceeded Darwinian selection. Thusly, our environments that we have made for ourselves (and that we assume that heighten our QoL) actually cause the reverse, all the while top researchers are scratching their heads to figure out the answer, the problem while it’s staring them right in the face.
Our obesogenic environments have literally created a mismatch with our current eating habits and our ancestral one (Krebs, 2009). Moreover, dietary mismatches occur when cultural and technological change vastly outstrip biological evolution (Logan and Jacka, 2009). Clearly, we need to lessen the impact of our obesogenic environment we have made for ourselves so that we can live as long as possible, as well as be as cognitively sharp as possible. Thusly, if our environment causes a mismatch with our genome which in turn causes obesity, then by changing our environment to one that matches our genome, so to speak, levels of obesity should decline as our environment becomes less obesogenic while becoming like our ancestral environment (Genne-Bacon, 2014).
In sum, the evidence for the positive benefits for exercise is ever-mounting (not like you need Pubmed studies to know that exercise is beneficial). However, due to our obesogenic environments, this makes it hard for people with higher time preference to resist their urges and the result is what you see around you today. The evidence is clear: exercise leads to increased blood flow to our vampiric brains; thus it will have positive effects on memory and other cognitive faculties. So, in order to live to a ripe, old age as a healthy man/woman, hit the gym and treadmill and try staying away from evolutionarily novel things as much as possible (i.e., like processed food). When we, as a country recognize this, we can then be smarter, healthier and, above all else, have a high QoL while living a longer life. Is that not what we all want? Well hit the gym, start exercising and change your diet to one that matches our ancestors. Don’t be that guy/gal (we all know who that guy is) that jumps on the exercise train late and misses out on these cognitive and lifestyle benefits!
Note: Only with Doctor supervision, of course
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