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Large prey extinction drove evolutionary changes in early humans

A new study led by Tel Aviv University (TAU) has found that the extinction of large prey, upon which human nutrition depended hundreds of thousand years ago, compelled prehistoric humans to develop improved weapons to help them hunt smaller prey, thus driving significant evolutionary adaptations. 

By examining the evolution of hunting weapons from wooden- and stone-tipped spears to sophisticated bows and arrows, the experts found significant correlations with changes in prey size and human physiology and culture.

Focus of the study 

“This study was designed to examine a broader unifying hypothesis, which we proposed in a previous paper published in 2021. The hypothesis explains the cultural and physiological evolution of prehistoric humans – including increased cognitive abilities – as an adaptational response to the need to hunt progressively smaller and quicker prey,” the authors wrote.

“So far such a unified hypothesis was lacking in professional literature, with the prevailing hypothesis maintaining that the changes in hunting weapons were a reflection of an essentially unexplained cognitive improvement.”

The researchers analyzed findings from nine prehistoric archaeological sites from South Africa, East Africa, Spain, and France. Early humans inhabited the sites about 300,000 years ago, during the transition from the Lower to the Middle Stone Age (Paleolithic). This was a period in which Neanderthals and Homo Sapiens first emerged.

Decline in size of large prey

The analysis of animal bones and stone tools used to hunt and process prey revealed a strong correlation between the emergence of stone-tipped spears, and the progressive decline in prey size.

“Specifically, we examined the emergence of a sophisticated stone-knapping method known as the Levallois technique, which is especially indicative of cognitive development: unlike earlier knapping methods, here the craftsman first prepares a core of good-quality stone, then cuts a pointed item off with one stroke – a process that requires him/her to imagine the final outcome in advance,” said the researchers.

“We found that in all cases, at all sites, stone tips made with the Levallois technology appeared simultaneously with a relative decrease in the quantity of bones of large prey.”

Wooden spears 

According to lead author Miki Ben-Dor, an archeologist at TAU, studies of contemporary hunter-gatherers suggest that wooden spears are sufficient for hunting large prey such as elephants. 

After first limiting the animal’s mobility – for instance, by driving it into a swamp or digging a trapping pit and concealing it with branches – the hunters can then thrust a spear into it and wait for it to bleed. However, middle-sized animals such as deer, are much more difficult to trap, and if hit by a wooden spear, they have more chances to run away. 

Stone-tipped spears 

Thus, more substantial wounds induced by stone-tipped spears are likely to slow them down and reduce the distance they can run before collapsing.

Archeological evidence suggests that prehistoric humans began to manufacture stone tools about three million years ago, and started to hunt about two million years ago. 

While Homo Erectus (the ancestor of all later types of humans) used wooden spears, Neanderthals and Homo Sapiens upgraded their spears around 300,000 years ago by adding stone tips produced with the more sophisticated Levallois method. 

More complex hunting systems 

Around 50,000 years ago, people developed more complex hunting systems. Homo Sapiens began using bows, arrows, and spear throwers. Finally, at the end of the Upper Paleolithic (approximately 25,000 years ago), new hunting aids emerged, including dogs, traps, and fishing hooks. 

While facts about this continual evolution of hunting weapons – accompanied by improvements in human cognition and skills – have been known for a long time, no unifying hypothesis for explaining them has been proposed.

Evolution of prehistoric humans 

“For the past ten years we have been searching for a unified explanation for focal phenomena in the cultural and biological evolution of prehistoric humans,” said co-author Ran Barkai, an archeologist at TAU.

“Our excavations at the Qesem Cave site led us to conclude that elephants, a major component of the human diet in our region for a million years, disappeared about 300,000 years ago, as a result of overhunting and climate change. With the huge elephants gone, humans had to find ways for obtaining the same amount of calories from a larger number of smaller animals.”

“Ultimately, we hypothesized that prey size had played a major part in human evolution: at the beginning the largest animals were hunted, and when these were gone humans went on to the next in size, and so on. Finally, when hunting was no longer energetically viable, humans began to domesticate animals and plants. That’s how the agricultural revolution began.”

Large prey decline and hunting weapons 

In 2021, Barkai and Ben-Dor first proposed their unified hypothesis on the cultural and physiological development of Paleolithic humans, by connecting advancements in hunting weapons to decreases in prey size. 

Their recent research supports this theory and builds upon a previous 2022 study they conducted alongside zoologists Jacob Dambitzer and Shai Meiri from TAU. This study examined archaeological data spanning 1,500,000 to 20,000 years ago, revealing a shift in predominant prey – from 12-ton elephants at the start of this period to 25 kg gazelles by the end. 

Additionally, the data indicated that the average prey weight dropped from three tons a million years ago to just 50 kg 20,000 years ago, highlighting a consistent reduction in prey size.

“In the present study specifically, and in our broader unifying hypothesis in general, we propose for the first time an explanation for one of the most intriguing questions in prehistoric archaeology: Why did tools change? The usual explanation is that tools changed due to improvements in the cognitive abilities of humans. For instance, when humans were suddenly able to imagine the outcomes of a sophisticated process, they developed the Levallois technique,” said Barkai.

“But one may well ask: Why did humans become smarter all of a sudden? What was the advantage of having a large brain that consumes so much energy? We demonstrate that these biological and cognitive changes correlate directly with the size of prey.”

Small elusive animals 

“To hunt small elusive animals humans had to become smarter, faster, more focused, more observant, and more collaborative. They had to develop new weapons for hunting from afar and learn how to track their prey.” 

“And they had to choose their prey carefully, with preference for high fat content, to ensure a sufficient energetic return – because hunting a large number of agile gazelles requires a much higher investment of energy than hunting one giant elephant.”

“This, we propose, is the evolutionary pressure that generated the improvement in human ability and tools – to ensure an adequate energy return on investment (EROI).”

The study is published in the journal Quaternary.

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