During the Pleistocene period, between 2.6 million years ago and 11,700 years ago, the brains of humans and their relatives grew. Now scientists from Tel Aviv University have a new hypothesis as to: While the largest animals in the landscape have disappeared, the scientists suggest: human brains had to grow to allow the hunting of smaller, faster prey.
This hypothesis argues that early humans specialized in capturing the largest animals, such as elephant, which would provide adequate fatty meals. As the numbers of these animals declined, people with larger brains, who presumably had more brain power, were better able to adapt and capture smaller prey, leading to better survival for the brainiacs.
Eventually, adult human brains expanded from an average of 40 cubic centimeters (650 cubic centimeters) about 2 million years ago to about 92 cubic centimeters (1500 cubic centimeters) at the height of the agricultural revolution about 10,000 years ago. The hypothesis also explains why the brain size shrank slightly to about 80 cubic centimeters (1300 cubic cm) after farming began: the extra tissue was no longer needed to maximize hunting success.
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This new hypothesis holds a trend in studies of human origin. Many scholars in the field now argue that human brains have grown in response to very small pressures, rather than one large one. But Tel Aviv University archaeologists Miki Ben-Dor and Ran Barkai argue that one major change in the environment would provide a better explanation.
“We see the decline in prey size as a collaborative statement not only for brain expansion but also for many other transformations in human biology and culture, and we argue that it provides a good incentive for these changes,” Barkai said in wrote an email to Live Science. . “[Scholars of human origins] is not used to looking for a single explanation that will cover a variety of adjustments. We believe it is time to think differently. ‘
Big prey, growing brains
The growth of the human brain is evolutionarily outstanding because the brain is an expensive organ. The Homo sapiens brain uses 20% of the body’s oxygen at rest, despite the fact that it makes up only 2% of the body’s weight. An average human brain today weighs 2.98 kg. (1 352 grams), which is the brain of chimpanzees, our closest living relatives, much higher than 384 grams.
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The hypothesis of Barkai and Ben-Dor depends on the idea that human ancestors, beginning with Homo habilis and peak with Homo erectus, the early Pleistocene as expert carnivores, taking down the largest, slowest prey offered by Africa. Megaherbivores, the researchers point out in an article published in the journal on March 5 Yearbook of Physical Anthropology, would have provided enough calories and nutrients with less effort than feeding plants or crawling smaller prey. Barkai and Ben-Dor say that modern humans digest fat better than other primates, and the physiology of humans, including stomach acidity and intestinal obstruction, suggests adaptations to eating fatty meats.
In another article, published on February 19 in the magazine Quarter, the researchers argue that human species’ tools and lifestyles are consistent with the shift from large prey to small prey. In Barkai’s fieldwork in Africa, for example, he found Homo erectus sites littered with elephant bones, which disappeared on later sites between 200,000 and 400,000 years ago. Ben-Dor wrote in an email to Live Science that the human ancestors at the more recent sites mostly ate fallow deer.
Generally, megaherbivores weigh more than 2200 pounds. (1,000 kilograms) began to decline in Africa about 4.6 million years ago, with herbivores weighing more than 770 pounds. (350 kg) which declined about 1 million years ago, the researchers wrote in their paper. It is not clear what caused this deterioration, but it could have been climate change, human hunting or a combination of the two. As the largest, slowest, and fattest animals disappeared from the landscape, humans would be forced to adapt by switching to smaller animals. According to the researchers, this link would have put evolutionary pressure on human brains to become larger because hunting of small animals would have been more complicated, as smaller prey is more difficult to detect and capture.
These growing brains would then explain many of the behavioral changes in the Pleistocene. Hunters of small, navy prey may have needed to develop language and complex social structures to successfully communicate and locate the place of prey. Better control over fire would have enabled human ancestors to extract as many calories from smaller animals as possible, including fat and oil from their bones. Tool and weapon technology would have to progress, according to Barkai and Ben-Dor, to enable hunters to pull down small game and attract small ones.
A fuzzy past
However, some hypotheses for human brain evolution have not held up well in the past, says Richard Potts, a paleoanthropologist and head of the Smithsonian’s Human Origins Program in Washington, DC, who was not involved in the research. And there are debates about many of the arguments in the new hypothesis. Potts, for example, told WordsSideKick that it was not at all clear whether early humans hunted megaherbivores at all. There are human cuts on large mammalian bones in some areas, but no one knows if the people killed or removed the animals.
The researchers sometimes use arguments from one period that may not apply to earlier times and places, Potts said. The evidence, for example, points to a preference for large prey by Neanderthals living in Europe 400,000 years ago, which would serve the human family well in winter, when plants were scarce. But the same would not be true in tropical Africa a few hundred thousand or a million years earlier, Potts said.
And when it comes to brains, size is not everything. To complicate the picture, brain shape also developed over the Pleistocene, and some relatives – such as Homo floresiensis, which between 60,000 and 100,000 years ago in what is now Indonesia – had small brains. H. floresiensis hunted small elephants and large rodents despite the small brain.
The period in which people and their family members experienced this brain expansion is poorly understood, with few fossil records. For example, there are perhaps three or four sites in Africa that were dated between 300,000 and 400,000 years ago that are definitely related to humans and their ancestors, said John Hawks, a paleoanthropologist at the University of Wisconsin-Madison, who did not was involved in the investigation and was skeptical about its conclusions. The human pedigree is complex in the course of the Pleistocene, with many branches, and the growth in brain size was not linear. The decline in large animals was also not, Hawks told WordsSideKick.
“They sketched a picture in which the megaherbivores deteriorate and the brain grows, and if you look at it through a telescope, it looks like it’s true,” Hawks told WordsSideKick. “But if you look at the details on either side, the brain size was more complicated, megaherbivores more complicated and it’s not like we can draw a straightforward relationship between them.”
However, the newspaper draws attention to the fact that human species may have hunted large mammals during the Pleistocene, Hawks said. There is a natural prejudice on fossil sites against the conservation of large mammals, because hunters or scavengers would not have dragged an entire elephant back to camp; they would rather have cut off packets of meat, leaving no evidence of the festival in their homes for future paleontologists and archaeologists.
“I’m sure we’re going to talk more and more about what the role of megaherbivores was in human existence, and was it important for us to become human?” Falcons said.
Originally published on Live Science.