Our ancestors’ diets changed dramatically over the course of the past 2.5 million years, and one research team thinks that profoundly affected our evolution.
According to a team including Miki Ben-Dor and Ran Barkai at Tel Aviv University in Israel, hominin diets were once so dominated by meat from massive animals that the hunters caused some of those species to go extinct. This, in turn, forced our ancestors to develop more sophisticated hunting techniques to bring down smaller, more elusive prey, leading to greater intelligence and the evolution of modern humans.
“The key idea is that just one ecological driver drove all of human evolution,” says Ben-Dor. “The one driver is the decline in prey size.”
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The team has drawn on an impressive range of evidence, says Sherry Nelson at the University of New Mexico. “But I wasn’t convinced”, she says, arguing that too often the researchers cited a paper in support of their hypothesis without considering alternative hypotheses.
Modern humans (Homo sapiens) have been around for about 300,000 years. We evolved from earlier members of the Homo genus, like Homo erectus, which are thought to have arisen from the more ape-like Australopithecus hominins. The earliest known Homo remains are 2.8 million years old.
Ben-Dor and his colleagues compiled evidence on what past hominins ate. This included traces of foods preserved on teeth, animal bones with cut marks suggesting butchery and chemical analyses of preserved hominin protein.
They concluded that Australopithecus ate mostly plants. However, early Homo species ate more meat, with H. erectus – the first species known to have expanded beyond Africa – consuming the most meat of all. When our speciesĚýfirst appeared, meat was still a large dietary component, but within the past 50,000 years, we began eating less.
In a second study, published in February, Ben-Dor and Barkai argue that early hominins like H. erectus were mostly hunting like . This, they say, only required simple weapons like wooden spears. “You probably need more courage to hunt an elephant than to hunt a zebra, but it’s less complex,” says Ben-Dor.
However, he points to a 2019 study that found that the , beginning 4.5 million years ago. He argues that hunting by hominins contributed to that decline. As the largest animals became rarer, hominins had to hunt smaller, nimbler animals. That required better technology, such as the bows and arrows used by present-day hunter-gatherers, which necessitated the evolution of greater intelligence.
It’s “an interesting hypothesis”, says Nelson. Parts of it do fit the evidence, she says. For instance, Australopithecus seems to have had big guts, similar to plant-eating apes like chimps and gorillas, while there is evidence that early Homo was eating more meat.
But Nelson isn’t convinced that H. erectus was regularly hunting the largest animals. “Going after big game like that implies a significant level of cooperation and coordination and planning,” she says, even if it doesn’t need complex tools.
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Instead, H. erectus diets may have improved because they learned to use fire to cook food. There is no evidence of hominins using fire that early, but Nelson says present-day hunter-gatherers often make short-lived fires, which wouldn’t be preserved.
Nelson also questions whether the sequence of events lines up with the hypothesis. Most of the megafauna extinctions happened within the past 25,000 years, long after H. erectus itself had become extinct. By 25,000 years ago, H. sapiens had long since evolved big brains. “That doesn’t really fit,” she says.
Journal references: American Journal of Physical Anthropology, ; Quaternary,
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