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Would dinosaurs have reached human-like intellect had the K-T extinction (an asteroid impact near the Yucatan peninsula) not occurred? One researcher believes so, and he believes that a dinosaur called the troodon would have evolved into a bipedal, human-like being. This is, of course, the old progressive evolution shtick. This assumes that a man-like being is an inevitability, and that sentience is a forgone conclusion.

This belief largely comes from Rushton’s citation of one Dale Russel, the discoverer of the dinosaur the troodon:

Paleontologist Dale Russell (1983,1989) quantified increasing neurological complexity through 700 million years of Earth history in invertebrates and vertebrates alike. The trend was increasing encephalization among the dinosaurs that existed for 140 million years and vanished 65 million years ago. Russell (1989) proposed that if they had not gone extinct, dinosaurs would have progressed to a large-brained, bipedal descendent. For living mammals he set the mean encephalization, the ratio of brain size to body size, at 1.00, and calculated that 65 million years ago it was only about 0.30. Encephalization quotients for living molluscs vary between 0.043 and 0.31, and for living insects between 0.008 and 0.045 but in these groups the less encephalized living species resemble forms that appeared relatively early in the geologic record, and the more encephalized species resemble those that appeared later. (Rushton, 1997: 294)

This argument is simple to rebut. What is being described is complexity. The simplest possible organism are bacteria, which reside at the left wall of complexity. The left wall “induces right-skewed distributions”, whereas the right wall induces “left-skewed distributions” (Gould, 1996: 55). Knowing this, biological complexity is a forgone conclusion, which exists at the extreme end of the right tail curve. I’ve covered this in my article Complexity, Walls, 0.400 Hitting and Evolutionary “Progress”

Talking about what Troodons may have looked like (highly, highly, doubtful. The anthropometric bias was pretty strong) is a waste of time. I’ve stated this a few times and I’ll state it yet again: without our primate body plan, our brains are pretty much useless. Our body needs our brain; our brain needs our body. Troodons would have stayed quadrupedal; they wouldn’t have gone bipedal.

He claims that some dinosaurs would have eventually reached an EQ of humans—specifically the troodon. They had EQs about 6 times higher than the average dinosaur, had fingers to grasp, had small teeth, ate meat, and appeared to be social. Dale Russel claims that had the K-T extinction not occurred, the troodon would look similar to us with a brain size around 1100 cc (the size of erectus before he went extinct). This is what he believes the dinosauroid troodon would look like had they not died out 65 mya:

When interviewed about the dinosauroid he imagined, he stated:

The “dinosauroid” was a thought experiment, based on an observable, general trend toward larger relative brain size in terrestrial vertebrates through geologic time, and the energetic efficiency of an upright posture in slow-moving, bipedal animals. It seems to me that such speculation remains acceptable, particularly if directed toward non-anthropoid anatomical configurations. However, I very nearly decided not to publish the exercise because of the damaging effects it might have had on the credibility of my work in general. Most people remained polite, although there were hostile reactions from those with “ultra-quantitative” and “ultra-intuitive” world views.

Why does it look so human? Why does he assume that the ‘ideal body plan’ is what we have? It seems to be extremely biased towards a humanoid morphology, just as other reconstructions are biased towards what we think about certain areas today and how the people may have looked in our evolutionary past. Anthropocentric bias permeates deep in evolutionary thinking, this is one such example.

Thinking of this thought experiment of a possible ‘bipedal dinosauroid’ we need to be realistic in terms of thinking of its anatomy and morphology.

Let’s accept Russel’s contention as true; that troodontids or other ‘highly encephalized species’ reached a human EQ, as he notes, of 9.4, with troodontids at .34 (the highest), archaeopteryx at .32, triconodonts (early extinct mammal of the cretaceous) with a .29 EQ, and the diademodon with an EQ of .20 (Russel, 1983). Russel found that the troodontids had EQs 6 times higher than the average dinosaur, so from here, he extrapolated that the troodon would have had a brain our size. However, Stephen Jay Gould argued the opposite in Wonderful Life writing:

If mammals had arisen late and helped to drive dinosaurs to their doom, then we could legitimately propose a scenario of expected progress. But dinosaurs remained dominant and probably became extinct only as a quirky result of the most unpredictable of all events—a mass dying triggered by extraterrestrial impact. If dinosaurs had not died in this event, they would probably still dominate the large-bodied vertebrates, as they had for so long with such conspicuous success, and mammals would still be small creatures in the interstices of their world. This situation prevailed for one hundred million years, why not sixty million more? Since dinosaurs were not moving towards markedly larger brains, and since such a prospect may lay outside the capability of reptilian design (Jerison, 1973; Hopson, 1977), we must assume that consciousness would not have evolved on our planet if a cosmic catastrophe had not claimed the dinosaurs as victims. In an entirely literal sense, we owe our existence, as large reasoning mammals, to our lucky stars. (Gould, 1989: 318)

If a large brain was probably outside of reptilian design, then a dinosaur—or a descendant (troodon included)—would have never reached human-like intelligence. However, some people may say that dinosaur descendants may have evolved brains our size since birds have brains that lie outside of reptilian design (supposedly).

However, one of the most famous fossils ever found, archaeopteryx, was within reptilian design, having feathers and along with wings which would have been used for gliding (whether or not they flew is debated). Birds descend from therapods. Anchiornis, and other older species are thought to be the first birds. Most of birds’ traits, such as bipedal posture, hinged ankles, hollow bones and S-shaped neck in birds are derived features from their ancestors.

If we didn’t exist, then if any organism were to come close to our intelligence, I would bet that some corvids would, seeing as they have a higher packing density and interconnections compared to the “layered mammalian brain” (Olkowicz et al, 2016). Nick Lane, biochemist and author of the book The Vital Question: Evolution and the Origins of Complex Life believes a type of intelligent ocotopi may have evolved, writing:

Wind back the clock to Cambrian times, half a billion years ago, when mammals first exploded into the fossil record, and let it play forwards again. Would that parallel be similar to our own? Perhaps the hills would be crawling with giant terrestrial octopuses. (Lane, 2015: 21)

We exist because we are primates. Our brains are scaled-up primate brains (Herculano-Houzel, 2009). Our primate morphology—along with our diet, sociality, and culture—is also why we came to take over the world. Our body plan—which, as far as we know, only evolved once—is why we have the ability to manipulate our environment and use our superior intelligence—which is due to the number of neurons in our cerebral cortex, the highest in the animal kingdom, 16 billion in all (Herculano-Houzel, 2009). Why postulate that a dinosaur could have looked even anywhere close to us?

This is also ignoring the fact that decimation and diversification also ‘decide the fates’ so to speak, of the species on earth. Survival during an extinction event is strongly predicated by chance (and size). The smaller an organism is, the more likely it will survive an extinction event. Who’s to say that the troodon doesn’t go extinct due to an act of contingency, say, 50 mya if the K-T extinction never occurred?

In conclusion, the supposed ‘trend’ in brain size evolution is just random fluctuations—inevitabilities since life began at the left wall of complexity. Gould wrote about a drunkard’s walk in his book Full House (Gould, 1996) in which he illustrates an example of a drunkard walking away from a bar with the bar wall being the left wall of complexity and the gutter being the right wall. The gutter will always be reached; and if he hits the wall, he will lean against the wall “until a subsequent stagger propels him in the other direction. In other words, only one direction of movement remains open for continuous advance—toward the gutter” (Gould, 1996: 150).

I bring up this old example to illustrate but one salient point: In a system of linear motion structurally constrained by a wall at one end, random movement, with no preferred directionality whatever, will inevitably propel the average position away from a starting point at the wall. The drunkard falls into the gutter every time, but his motion includes no trend whatever toward this form of perdition. Similarly, some average or extreme measure of life might move in a particular direction even if no evolutionary advantage, and no inherent trend, favor that pathway (Gould, 1996: 151).

We humans are lucky we are here. Contingencies of ‘just history’ are why we are here, and if we were not here—if the K-T extinction never occurred—and the troodon or another dinosaur species survived to the present day, they would not have reached our ‘level’ of intelligence. To believe so is to believe in teleological evolution—which certainly is not true. Anthropometric bias runs deep in evolutionary biology and paleontology. People assume that since we are—according to some—the ‘pinnacle’ of evolution, that us, or something like us, would eventually have evolved.

Any ‘trends’ can be explained as life moving away from the left wall of complexity, with the left wall—the mode of life, the modal bacter-–being unchanged. We are at the extreme tail of the distribution of complexity while bacteria are at the left wall. Complex life was inevitable since bacteria, the most simple life, began at the left wall. And so, these ‘trends’ in brain size are just that, increasing complexity, not any type of ‘progressive evolution’. Evolution just happens, natural selection occurs based on the local environment, not any inherent or intrinsic ‘progress’.

References

Gould, S. J. (1989). Wonderful life: the burgess Shale and the nature of history. New York: Norton.

Gould, S. J. (1996). Full house: The Spread of Excellence from Plato to Darwin. New York: Harmony Books.

Herculano-Houzel, S. (2009). The human brain in numbers: a linearly scaled-up primate brain. Frontiers in Human Neuroscience,3. doi:10.3389/neuro.09.031.2009

Lane, N. (2015). The vital question: energy, evolution, and the origins of complex life. New York: W.W. Norton & Company.

Olkowicz, S., Kocourek, M., Lučan, R. K., Porteš, M., Fitch, W. T., Herculano-Houzel, S., & Němec, P. (2016). Birds have primate-like numbers of neurons in the forebrain. Proceedings of the National Academy of Sciences,113(26), 7255-7260. doi:10.1073/pnas.1517131113

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

Russell, D. A. (1983). Exponential evolution: Implications for intelligent extraterrestrial life. Advances in Space Research,3(9), 95-103. doi:10.1016/0273-1177(83)90045-5

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Tl;dr: The ‘trend’ in the evolution of hominin brain size is only due to diet quality and abundance. If there is any scarcity of food or a decrease in nutritional quality, there will be a subsequent decrease in brain size, as seen with H. floresiensis. Brain size, contrary to popular belief, has been decreasing for the past 20,000 years and has accelerated in the past 10,000. This trend is noticed all over the world with multiple hypotheses put out to explain the phenomenon. Despite this, people still deny that a decrease is occurring. Is it? Yes, it is. It’s due to a decrease in diet quality along with higher population density. If the human diet were to decrease in quality and caloric amount, our brains—along with our bodies—would become smaller over time.

Is there progress in hominin brain evolution? Many people may say yes. Over the past 7 million years, the human brain has tripled in size with most of this change occurring within the past 2 million years. This perfectly coincides with the advent of bipedalism, tool-making, fire, cooking and meat eating. Knowing the causal mechanisms behind the increase in hominin (primate) brain size, is there ‘progress’ to brain size in hominin evolution?

Looking at the evolution of hominin brain size in the past 7 million years, one can rightfully make the case that there is an evolutionary trend with the brain size increase. I don’t deny there is an increase, but first, before one says there is ‘progress’ to this phenomenon, you must look at it from both sides.

Montgomeroy et al (2010) reconstructed the ‘ups and downs’ of primate brain size evolution, and of course, decreases in hominin brain size can’t be talked about without bringing up H. floresiensis and his small brain and body mass, which they discuss as well. They come to the conclusion that “brain expansion began early in primate evolution”, also showing that there have been brain size increases in all clades of primates. Humans only show a bigger increase in absolute mass, with rate of proportional change in mass and relative brain size “having greater episodes of expansion elsewhere on the primate phylogeny”. Decreases in brain size also occurred in all of the major primate clades studied, they conclude that “while selection has acted to enlarge primate brains, in some lineages this trend has been reversed.” The selection can only occur in the presence of adequate kcal, keeping everyone sated and nourished enough to provide for the family, ensuring a woman gets adequate kcal and nutrients during pregnancy and finally ensuring that the baby gets the proper amount of energy for growth during infancy and childhood.

Montgomery et al write:

The branch with the highest rate of change in absolute brain mass is the terminal human branch (140,000 mg/million years). However for rate of proportional change in absolute brain mass the human branch comes only fourth, below the branches between the last common ancestor of Macaques and other Papionini, and the last common ancestor of baboons, mangabeys and mandrills (48 to 49), the ancestral primate and ancestral haplorhine (38 to 39) and the branch between the last common ancestor of Cebinae, Aotinae and Callitrichidae, and the ancestral Cebinae (58 to 60). The rate of change in relative brain mass along the human branch (0.068/million years) is also exceeded by the branch between the last common ancestor of Alouatta, Ateles and Lagothrix with the last common ancestor of Ateles and Lagothrix (branch 55 to 56; 0.73), the branch connecting the last common ancestor of Cebinae, Aotinae and Callitrichidae, and the ancestral Cebinae (branch 58 to 60; 0.074/million years) and the branch connecting the last common ancestor of the Papionini with the last common ancestor of Papio, Mandrillus and Cercocebus (branch 48 to 49; 0.084). We therefore conclude that only in terms of absolute mass and the rate of change in absolute mass has the increase in brain size been exceptional along the terminal branch leading to humans. Once scaling effects with body mass have been accounted for the rate of increase in relative brain mass remains high but is not exceptional.

“Remains high but is not exceptional”, ie, expected for a primate of our size (Azevedo et al, 2009). Of course, since evolution is not progressive, then finding any so-called ‘anomalies’ that ‘deviate’ from the ‘progress’ in brain size evolution makes sense. They conclude that floresiensis’ brain size and body mass decrease fell within the expected range of Argue et al’s (2009) proposed phylogenetic scenario. Though, only if he evolved from habilis or Dmansi hominins if the insular dwarfism hypothesis was taken into account (which is a viable explanation for the decrease).

The effects of food scarcity and its effect on hominin brain size is hardly ever spoken about. However, as I’ve been documenting here recently, caloric quality and amount dictate brain size. Montgomeory et al (2010) write:

Although many studies have investigated the possible selective advantages and disadvantages of increased brain size in primates [5, 17, 18, 19, 20, 21], few consider how frequently brain size has reduced. Periods of primate evolution which show decreases in brain size are of great interest as they may yield insights into the selective pressures and developmental constraints acting on brain size. Bauchot & Stephan [22] noted the evolution of reduced brain size in the dwarf Old World monkey Miopithecus talapoin and Martin [23] suggested relative brain size in great apes may have undergone a reduction based on the cranial capacity of the extinct hominoid Proconsul africanus. Taylor & van Schaik [24]reported a reduced cranial capacity in Pongo pygmaeus morio compared to other Orang-utan populations and hypothesise this reduction is selected for as a result of scarcity of food. Finally, Henneberg [25] has shown that during the late Pleistocene human absolute brain size has decreased by 10%, accompanied by a parallel decrease in body size.

[…]

These authors suggest this reduction is associated with an increase in periods of food scarcity resulting in selection to minimise brain tissue which is metabolically expensive [17]. Food scarcity is also believed to have played a role in the decrease in brain size in the island bovid Myotragus [12]. Taylor & van Schaik [24] therefore propose that H. floresiensis may have experienced similar selective pressures as Myotragus and Pongo p. morio.

Nice empirical vindication for me, if I don’t say so myself. This lends further credence to my scenario of an asteroid impact on earth halting food production leading to a scarcity in food. It’s hypothesized that floresiensis went from eating (if evolved from erectus) 1800 kcal per day and 2500 while nursing to 1200 per day and 1400 while nursing (Lieberman, 2013: 125). This, again, is proof that big brains need adequate energy and that cooking meat was what specifically drove this facet of our evolution.

Montgomeroy et al (2010) conclude:

Finally, our analyses add to the growing number of studies that conclude that the evolution of the human brain size has not been anomalous when compared to general primate brain evolution [59, 61, 91, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94].

In other words, humans are not ‘special’ in terms of brain size. While there is a ‘trend’ in the increase in brain size, this ‘trend’ is only possible with the advent of fire, cooking, and meat eating. Without that causal mechanism, big brains would not be metabolically viable.

A big brain (large amounts of neurons) can only evolve with enough energy, mainly the advent of cooking meat (Herculano-Houzel, 2009). Primates have much higher neuronal densities than other mammals (Herculano-Houzel, Manger, and Kaas, 2014). Since the amount of energy the brain needs per day depends on how many total neurons it has (Azevedo and Herculano-Houzel, 2012), quality calories are needed to power such a metabolically expensive organ. Only with the advent of fire could we consume enough high-quality energy to evolve such big brains.

Mammalian brains that have 100 million neurons require .6 kcal, brains with 1 billion neurons use 6 kcal per day, and brains with 100 billion neurons use 600 kcal per day (humans with 86 billion neurons use 519 kcal, coming out to 6 kcal per neuron) regardless of the volumes of the brains (Herculano-Houzel, 2011). Knowing that the amount of neurons a brain has is directly related to how much energy it needs, it doesn’t seem so crazy now that, like with the example of floresiensis, a brain could decrease in size even when noticing this ‘upward trend’ in hominin brain size. This is simply because how big a brain is directly related to amount of energy available in an area as well as the most important variable: quality of the food.

If floresiensis is descended from habilis (and there is evidence that habilis was a meat eater, so along with a low amount of energy for floresiensis on Flora as well as there being no large predators on the island, a smaller size would have been advantageous to floresiensis), then this shows that what I’ve been saying for a few months is true: the diet quality as well as amount of energy dictates whether an organism evolves to be big or small. Energy is what ‘drives’ evolution in a sense and energy comes from kcal. The highest quality energy is from meat, and that fuels our ‘big brains’ with our high neuron count.

Imagine this scenario: an asteroid hits the earth and destroys the world power grid. All throughout the world, people cannot consume enough food. The sun is blocked by dust clouds for, say, 5000 years. The humans that survive this asteroid collision would evolve a smaller brain and body as well as better eyesight to see in an environment with low light, among other traits. Natural selection can only occur on the heritable variants already in the population, so whatever traits that would increase fitness in this scenario would multiply and flourish in the population, leading to a different, smaller-brained and smaller-bodied human due to the effects of the environment.

While on the subject of the decrease in human brain size, something that’s troubling to those who champion the ‘increase in hominin brain size’ as the ‘pinnacle of evolution’: our brains have been decreasing in size for at least the past 20,000 years according to John Hawks associate professor of anthropology at the University of Wisconsin-Madison. Keep in mind, this is someone that Pumpkin Person brings up saying that our brains have been increasing for the past 10,000 years. He has also said that the increase in better nutrition has allowed us to gain back the brain size of our hunter-gatherer ancestors (with no reference), which is not true. Because what John Hawks actually wrote on his blog about this says a different story:

The available skeletal samples show a reduction in endocranial volume or vault dimensions in Europe, southern Africa, China, and Australia during the Holocene. This reduction cannot be explained as an allometric consequence of reductions of body mass or stature in these populations. The large population numbers in these Holocene populations, particularly in post-agricultural Europe and China, rule out genetic drift as an explanation for smaller endocranial volume. This is likely to be true of African and Australian populations also, although the demographic information is less secure. Therefore, smaller endocranial volume was correlated with higher fitness during the recent evolution of these populations. Several hypotheses may explain the reduction of brain size in Holocene populations, and further work will be necessary to uncover the developmental and functional consequences of smaller brains.

Selection for smaller brains in Holocene human evolution

In fact, from the Discover article on decreasing brain size, John Hawks says:

Hawks spent last summer measuring skulls of Europeans dating from the Bronze Age, 4,000 years ago, to medieval times. Over that period the land became even more densely packed with people and, just as the Missouri team’s model predicts, the brain shrank more quickly than did overall body size, causing EQ values to fall. In short, Hawks documented the same trend as Geary and Bailey did in their older sample of fossils; in fact, the pattern he detected is even more pronounced. “Since the Bronze Age, the brain shrank a lot more than you would expect based on the decrease in body size,” Hawks reports. “For a brain as small as that found in the average European male today, the body would have to shrink to the size of a pygmy” to maintain proportional scaling.

This is in stark contrast to what PP claims he says about the evolution of human brain size over the past 10,000 years, especially Europeans who he claims Hawks has said there has been an increase in European brain size. An increase in brain size over the past 100 years doesn’t mean a trend is occurring upward, since all other data on human brain size says otherwise.

Our brains have begun to decrease in size, which is due to the effects of overnutrition and diseases of civilization brought on by processed foods and the agricultural revolution. Another proposed cause for this is that population density tracks with brain size, with brain size increasing with a smaller population and decreasing with a bigger population. In a way, this makes sense. A bigger brain should have more neurons than a smaller brain, which would aid in cognitive tasks and have that one hominin survive better giving it a better chance to pass on its genes, so if you think about it, when the population increases when social trust forms, you can piggyback off of others and they wouldn’t have to do things on their own. As population size increased from sparse to dense, brain size decreased with it.

On this notion of ‘progress’ in brain size, some people may assume that this puts us at the ‘pinnacle’ of evolution due to our superior cognitive ability (which is due to the remarkably large amount of neurons in our cerebral cortex [Hercualno-Houzel, 2016: 102]), Herculano-Houzel writes on page 91 of her book The Human Advantage: A New Understanding of How Our Brains Became Remarkable:

We have long deemed ourselves to be at the pinnacle of cognitive abilities among animals. But that is different than being at the pinnacle of evolution in a number of important ways. As Mark Twain pointed out in 1903, to presume that evolution has been a long path leading to humans as its crowning achievement is just as preposterous as presuming that the whole purpose of building the Eiffel Tower was to put the final coat of paint on its tip. Moreover, evolution is not synonmous with progress, but simply change over time. And humans aren’t even the youngest, most recently evolved species. For example, more than 500 new species of cichlid fish in Lake Victoria, the youngest of the great African Lakes, have appeared since it filled with water some 14,500 years ago.

Using PP’s logic, the cichlid fishes of Lake Victoria are ‘more highly evolved’ than we are since they’re a ‘newer species’. Using that line of logic makes no sense now, putting it in that way.

Looking at the ‘trend’ in human brain size over the past 7 million years, and its acceleration in the past 2 million, without thinking about what jumpstarted it (bipedalism, tools, fire, meat eating) is foolish. Moreover, any change to our environment that decreases our energy input would, over time, lead to a decrease in our overall brain size perhaps more rapidly, showing that this ‘trend’ in the increase in brain size is directly related to the quality and amount of food in the area. This is why floresiensis’ brain and body shrunk, and why certain primate lineages show increases in brain size: because they have a higher-quality diet. But it comes at a cost. Since primates largely eat a plant-based diet, they have to eat upwards of 10 hours a day to get enough energy to power either their brains or their bodies. If their bodies are large, their brains are small and vice versa. A plant-based diet cannot power a large brain with a high neuron count like we have, it’s only possible with meat eating (Azevedo and Herculano-Houzel, 2012). This is one reason why floresiensis’ brain shrunk along with not enough kcal to sustain their larger brain and body mass that their ancestor they evolved from previously had.

Our brains are not particularly special, and in a way, you can thank fire and cooking meat for everything that’s occurred since erectus first controlled fire. For without a quality diet in our evolution, this so-called ‘trend’ (which is based on the environment due to food quality and scarcity/abundance which fluctuate) would not have occurred. In sum, this ‘progress’ will halt and ‘reverse’ if the amount of energy consumed decreases or diet quality decreases.

1050 words

I wrote about bipedalism last week, however, in a conversation with a commented on PumpkinPerson’s blog, I came to a slightly different conclusion than I did in my previous article on the matter.

I quoted Daniel Liberman, author of the book The Story of the Human Body: Evolution, Health, and Disease:

As one might expect, other selective pressures are hypothesized to have favored bipedalism in the first hominins. Additional suggested advantages of being upright include improved abilities to make and use tools, to see over tall grass, to wade across streams, and even to swim. None of these hypotheses bear up under scrutiny. The oldest stone tools appear millions of years after bipedalism evolved.(Lieberman, 2013: 43)

However, after being linked to this journal article Shallow-water habitats as sources of fallback foods for hominins, I began to rethink my position on this matter.

Now, the climate change when humans and chimps diverged is still the primary cause of bipedalism, but after reading this abstract, I came to think that the climate change (getting warmer) rose the sea levels which then drove Man to walk on two legs, gather food, and, eventually, wade in water to find more food which led to some selection for bipedalism in our ancestors. Humans needed to become bipedal to find more food as the climate change made their primary food more scarce. This then drove early Man into shallow waters to look for food.

As the climate was getting warmer, the same foodstuffs we ate were not as readily available. So what drove us to be bipedal was 1) the need for immediate food, i.e., looking for food on the forest floors and 2) when adequate food could not be found on the floors of the forests, Man then had to go into the water. This had multiple advantages. One could escape from predators, find more food with adequate nutrients which, in turn, had as evolve bigger brains, and the most important aspect, it’s much easier to be bipedal in water as it’s easier to stand in water.

This paper, The evolution of the upright posture and gait—a review and a new synthesis, concludes:

Wading was an appropriate trigger not only to stand up but also forced the primate to walk on. It seems likely that habitual bipedalism began not long after the separation from the gorilla and chimpanzee clade(s). From that time onwards, throwing could be evolved with free upper extremities much more successfully than before. Selective factors related to the reduction of incoming solar radiation became effective. Endurance running and adaptations to carry tools (like weapons) started their evolutionary improvements. If these processes took about 4 Ma, the wading hypothesis is consistent with a rather perfect bipedal anatomy as shown, e.g., in Homo ergaster (WT 15000), about 1.6 Ma ago. In this way, many of the hypotheses competing in the past may be harmonised, as some of them have yielded important contributions to the understanding of the evolution of the human habitual upright gait.

The first sentence corroborates what Lieberman says in The Story of the Human Body. The final sentence brings together all of the theories that drove bipedalism in humans into a ‘new synthesis’.

Now, climate change (the earth getting warmer) is still the ultimate cause, but a proximate cause of bipedalism is wading in the water to 1) find more food and 2) escape predators.

This ‘new synthesis’ of how Man became bipedal is a great way to unify a lot of theories of bipedalism that gave us great understanding of human evolution in regards to bipedalism. In that vain, it’s like E.O. Wilson’s Sociobiology: A New Synthesis in which he sought to unify the evolutionary mechanics of altruism, aggression, and nurturance– our main social behaviors. This ‘new synthesis’ in the study of how we became bipedal unifies competing theories into a more understandable theory.

Moreover, bipedalism made it easier to consume more kcal which led to bigger brains. To quote Suzana Herculano-Houzel from her book The Human Advantage: A New Understanding of How Our Brain Became Remarkable:

“The remaining way to work around an energetic constraint to the number of neurons in the brain involves dietary changes that would allow for more calories to be obtained in the same amount of time, or even less. Some first changes in that direction probably took place 4 million years ago when our australopithecine ancestors stood upright and became habitual bipeds. As Daniel Lieberman explores in detail in The Story of the Human Body, bipedality potentially increases the amount of calories that can be amassed in a day by extending the range of food picking, for it is much easier and costs four times fewer kilocalories to walk on two feet, as humans do, than on all fours, as modern great apes do and the ancestor from which australopithecines originated must have done. Roaming away from home to find food, is the definition of a food gatherer, as opposed to a food picker, which is what great apes remain to this day. Bipedality made food gatherers of our ancestors.” (Herculano-Houzel, 2016: 189)

This graph from her book shows that bipedality preceded cooking which increased our brain size (I will write on that soon).

More neurons in the cerebral cortex is the cause for our amazing brains. But we are NOT unique!! This kcal increase led to more neurons in our cerebral cortex which then allowed for reasoning, finding patterns, developing technology and passing it on through culture. Cooking is why we are so ‘unique’ in comparison to other animals. As shown in the graph above, the increase in brain size happened around the time of H. Erectus. They show smaller teeth at that period, which shows that the selection was already occurring. The smaller teeth to break down food more to extract nutrients from the food they gathered shows that bipedalism evolved alongside the evolution of smaller teeth.

In sum, the ultimate cause of bipedality is still climate change, but the proximate cause, in part, was wading in the water which led to our ancestors to find more food. And, over time, we were selected for bipedalism as I wrote in my previous article on the matter. We can see that bipedalism slightly predated cooking, which the ultimate cause of which was to find more food. This is seen in the records we have. I will write more on this in the future as I read into this more.