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.
Pumpkin moderated my comment.
Excellent post you wrote, but i would not discount the Savannah hypothesis. Hominids more than likely started bipedalism for arboreal habitats and then it became useful for when food shortages caused them to trek through shallow water and open grasslands, this is consistent with the enormous climate change from wet to dry 4 million years ago.
“What kind of practice?”
Well I used t o live on a farm where there were a large number of stray cats, I would keep count of certain phenotypical variations that occurred through each generation and then started selecting for miniature versions of cats. It was successful for a while until I moved, when I came back to the location I found most of the cats were dead.
I also help my family in cross pollinating and eugenic experiments on their Hemp plants, I was able to Increase THC yield by 10% but honestly the small scale of the operation limits the potential level of results.
I don’t discount the Savannah hypothesis at all; just it makes sense that when humans and chimps split and the climate started getting warmer, the sea levels rose. When they couldn’t find food in the forest they went to shallow waters which helped with selection for bipedalism. Those who were able to adapt to the bipedality passed their genes and thus it was selected for as a positive trait. Clearly, a trait that huge would have not been selected out of the gene pool.
That’s cool man. I wish you luck in your studies. So you just took 2 small cats and breeded them? So you ended up getting the desired effect? Things like that, as well as the Russian fox experiment, show that evolution is true, no matter what creationists say.
LikeLiked by 1 person
“So you just took 2 small cats and breeded them? So you ended up getting the desired effect? Things like that, as well as the Russian fox experiment, show that evolution is true”
Kind of, I had litter of kittens and one of them took 4 or 5 years(long time for cats) before it reached it’s adult size. Even then, it was still 2/3 to 3/4 the size of the average short haired tabby cat. It had a sister so I kept an eye on her mating habits and simply chased any other male off until her midget brother finally figured out how to get down and dirty. The sister had another litter and 2 out of the litter were like the father(her brother) and I continuously interbred them. Every now and then I would introduce other cats to shuffle the genes a bit so that they wouldn’t develop abnormalities too severe. I eventually had to move but when I came back most of them were dead, I had learned they had lived a long life, however some had serious problems like hernias or seizures. Strangely enough only the father and mother still remained. I was able to make a total of 4 miniature cats, and was able to sell 1. I hope that doesn’t sound too crazy I wasn’t abusing them or anything I am a huge animal lover.
I don’t agree with this argument: ‘None of these hypotheses bear up under scrutiny. The oldest stone tools appear millions of years after bipedalism evolved.(Lieberman, 2013: 43)’
Creation of stone tools must have been a late development. Tool-making with softer, perishable materials would have predated crafted stone tools by a very long time. Stone is hard to work and requires a high skill level, even the simplest tools of the early type. To say that tool using wasn’t a factor, and then jump to stone tool making as proof, is ignoring the long preceding period before stone was worked.
I am not saying he is wrong. I don’t know enough to claim that. Just saying this argument is weak.