Human evolution; early diet and brain enlargement (Introduction)

by David Turell @, Monday, April 01, 2019, 21:00 (139 days ago) @ David Turell

Our larger brain takes 20% of our calorie intake. Early enlargement before Homo species certainly required a diet higher in calories. This theory about early butchery tries to cover that possibility:

https://www.scientificamerican.com/article/fat-not-meat-may-have-led-to-bigger-hominin-...

"Northern Ethiopia was once home to a vast, ancient lake.

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"Deposited within these layers are fossils: some of early hominins, along with the bones of hippos, antelope, and elephants. Anthropologist Jessica Thompson encountered two of these specimens, from an area named Dikika, in 2010.

"At the time, she was a visiting researcher at the Institute of Human Origins at Arizona State University. Given no explanation as to their history, she analyzed the bones and found signs of butchery. Percussion marks suggested someone may have accessed the marrow; cut marks hinted that flesh was stripped from bone. To her surprise, the specimens were 3.4 million years old, putting the butcher’s behaviors back 800,000 years earlier than conventional estimates would suggest. That fact got Thompson, now an assistant professor in the department of anthropology at Yale University, thinking there might be more traces of tool use from those early times.

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"The prevailing view, supported by a confluence of fossil evidence from sites in Ethiopia, is that the emergence of flaked tool use and meat consumption led to the cerebral expansion that kickstarted human evolution more than 2 million years ago. Thompson and her colleagues disagree: Rather than using sharpened stones to hunt and scrape meat from animals, they suggest, earlier hominins may have first bashed bones to harvest fatty nutrients from marrow and brains.

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"Because large animals such as antelope pack a serious micro-and-macro-nutrient punch, scientists have thought their meat contributed to humanity’s outsized brains. A consensus arose in the 1950s that our ancestors first hunted small animals before moving on to larger beasts around 2.6 million years ago. Flaked tool use and meat eating became defining characteristics of the Homo genus.

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"Then, starting in the mid-1980s, an opposing theory arose in which Homo’s emergence wasn’t so tightly coupled with the origins of hunting and predatory dominance. Rather, early hominins first accessed brain-feeding nutrients through scavenging large animal carcasses. The debate has rolled on through the decades, with evidence for the scavenging theory gradually building.

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"Marrow and brains, meanwhile, are locked inside bones and stay fresh longer. These highly nutritional parts are also a precursor to the fatty acids involved with brain and eye development. And more easily than flesh-meat, bones could be carried away from carcass sites, safe from predators.

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"she says, “This team has shown that marrow may have in fact been more important. It’s a nuance, but an important nuance.”

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"Evidence suggests hominins shifted their diet around 3.76 million years ago as they took advantage of the open spaces. By around 3.5 million years ago, some species of Australopithecus already showed increased brain sizes, up to 30 percent larger than chimpanzees of comparable body size. Canines had shrunk to proportions later seen in the genus Homo, and hand morphology was already more human than ape, with potential both for terrestrial travel and tool use.

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"The earliest Homo specimen is now dated to 2.8 million years. The Dikika fossils suggest butchery behaviors at 3.4 million years ago. Homo may have emerged earlier than scientists suspected—a theory that would need more fossil evidence to support it—or another hominin, such as Australopithecus, may have created tools before Homo."

Comment: It is important to recognize extra dietary calories al lowed brain growth, but didn't cause it.


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