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During the Pleistocene era, between 2.6 million years ago and 11,700 years ago, the brains of humans and their loved ones developed. Now, scientists at Tel Aviv University have a new hypothesis as to why: While the landscape’s largest animals have disappeared, scientists propose, human brains had to grow larger to allow the hunting of smaller and faster prey.
This hypothesis supports that early humans specialized in slaughtering larger animals, such as elephants, which would have provided many fatty meals. When the numbers of these animals declined, humans with larger brains, who presumably had more brains, were better able to adapt and capture smaller prey, which led to better brainiac survival.
Ultimately, the adult human brain went from an average of 40 cubic inches (650 cubic centimeters) 2 million years ago to around 92 cubic inches (1,500 cubic cm) at the dawn of the agricultural revolution. about 10,000 years ago. The hypothesis also explains why the size of the brain shrank slightly, to around 80 cubic inches (1,300 cubic cm), after farming began: the extra tissue was no longer needed to maximize the success of the hunt.
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This new hypothesis goes against a trend in studies of human origins. Many researchers in the field now argue that the human brain has developed in response to many small pressures, rather than just one large one. But Tel Aviv University archaeologists Miki Ben-Dor and Ran Barkai argue that a major change in the environment would provide a better explanation.
“We see the decrease in prey size as a unifying explanation of not only brain expansion, but many other transformations in human biology and culture, and we say this provides a good incentive for these changes.” , wrote Barkai in an email to Live Science. . “[Scholars of human origins] are not used to looking for a single explanation that will cover a variety of adaptations. It is time, we believe, to think differently. “
Big prey, growing brains
The growth of the human brain is evolutionarily exceptional because the brain is an expensive organ. The homo sapiens the brain uses 20% of the body’s oxygen at rest while it only represents 2% of the body’s weight. An average human brain today weighs 2.98 pounds. (1,352 grams), far surpassing the brains of chimpanzees, our closest living relatives, at 0.85 lbs (384 grams).
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The Barkai and Ben-Dor hypothesis is based on the idea that human ancestors, starting with Homo and culminating with Man standing, passed the beginning Pleistocene as expert carnivores, taking out the biggest and slowest prey Africa has to offer. Megaherbivores, say researchers in an article published on March 5 in the journal Yearbook of physical anthropology, would have provided enough calories and nutrients with less effort than foraging plants or stalking smaller prey. Modern humans digest fat better than other primates, Barkai and Ben-Dor said, and the physiology of humans, including stomach acidity and gut design, indicate adaptations for eating fat. fatty meat.
In another article, published on February 19 in the journal Quaternary, researchers say that the tools and way of life of human species are compatible with the transition from large prey to small prey. In Barkai’s fieldwork in Africa, for example, he found Man standing sites dotted with elephant bones, which disappeared at later sites 200,000 to 400,000 years ago. The human ancestors of these newer sites appeared to have primarily eaten deer, Ben-Dor wrote in an email to Live Science.
Overall, megaherbivores weighing over 2,200 pounds. (1,000 kilograms) began to decline across Africa around 4.6 million years ago, with herbivores weighing over 770 pounds. (350 kg) down about 1 million years ago, the researchers wrote in their article. It is not known what caused this decline, but it could have been climate change, human hunting, or a combination of the two. When the bigger, slower, and fatter animals disappeared from the landscape, humans would have been forced to adapt by switching to smaller animals. According to the researchers, this change would have put evolutionary pressure on the human brain to grow larger, as hunting small animals would have been more complicated, as smaller prey are more difficult to track and catch.
These growing brains would then explain many of the behavioral changes through the Pleistocene. Small prey hunters in the fleet may have needed to develop complex language and social structures to successfully communicate the location of the prey and coordinate its tracking. Better fire control would have allowed human ancestors to extract as many calories as possible from small animals, including fat and oil from their bones. Tool and weapon technology should have evolved to allow hunters to slaughter and dress small game, according to Barkai and Ben-Dor.
A hazy past
However, unique hypotheses for the evolution of the human brain have not held up well in the past, said Richard Potts, paleoanthropologist and manager of the Smithsonian’s Human Origins program in Washington, DC, who was not involved in the research. And there are debates on many arguments in the new hypothesis. For example, Potts told Live Science, it’s not clear whether early humans hunted megaherbivores. There are human cut marks on the bones of large mammals at some sites, but no one knows whether humans killed the animals or took them back.
Researchers also sometimes use arguments from a period that might not apply to earlier times and places, Potts said. For example, evidence suggests a preference for the large prey of Neanderthals living in Europe 400,000 years ago, which would have served these human relatives well in winter, when plants were scarce. But the same might not have been true a few hundred thousand or a million years earlier in tropical Africa, Potts said.
And when it comes to brains, size isn’t everything. Complicate the table, brain shape also evolved during the Pleistocene, and some human relatives – such as Homo floresiensis, who lived in what is now Indonesia between 60,000 and 100,000 years ago – had small brains. H. floresiensis hunted both small elephants and large rodents despite his small brain.
The period in which humans and their loved ones experienced this brain expansion is poorly understood, and few fossil records remain. For example, there are maybe three or four sites firmly dated to 300,000 to 400,000 years ago in Africa that are certainly linked to humans and their ancestors, said John Hawks, a paleoanthropologist at the University of Canada. Wisconsin-Madison who did not research and was skeptical of his findings. The human family tree was complicated during the Pleistocene, with many branches, and the growth in brain size was not linear. The declines in large animals haven’t been, either, Hawks told Live Science.
“They sketched a picture in which megaherbivores are declining and brains are increasing, and if you look at that through a telescope, it looks true,” Hawks told Live Science. “But actually, if you look at the details on either side, the size of the brain was more complicated, the megaherbivores were more complicated, and it’s not like we can relate directly to them.”
The document, however, draws attention to the fact that human species may indeed have hunted large mammals during the Pleistocene, Hawks said. There is a natural bias in the fossil sites against the preservation of large mammals, because human hunters or scavengers would not have brought an entire elephant back to camp; they would have sliced packets of meat instead, leaving no trace of the party at home for future paleontologists and archaeologists.
“I’m sure we’ll be talking more and more about the role of megaherbivores in human livelihoods, and were they important for us to become human?” Hawks said.
Originally posted on Live Science.
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