https://phys.org/news/2021-03-human-brain-grew-result-extinction.html

A new paper by Dr. Miki Ben-Dor and Prof. Ran Barkai from the Jacob M. Alkow Department of Archaeology at Tel Aviv University proposes an original
unifying
explanation for the physiological, behavioral and cultural evolution of the human species, from its first appearance about two million years ago, to the agricultural revolution (around 10,000 BCE). According to the paper, humans developed as hunters of large animals, causing their ultimate extinction.
As they
adapted to hunting small, swift prey animals, humans developed higher
cognitive
abilities, evidenced by the most obvious evolutionary change—the growth of brain volume from 650cc to 1,500cc. To date, no unifying explanation has been proposed for the major phenomena in human prehistory. The novel theory was published in Quaternary Journal.

In recent years more and more evidence has been accumulated to the effect
that
humans were a major factor in the extinction of large animals, and
consequently
had to adapt to hunting smaller game, first in Africa and later in all
other parts of
the world. In Africa, 2.6 million years ago, when humans first emerged,
the average
size of land mammals was close to 500kg. Just before the advent of
agriculture this
figure had decreased by over 90%—down to several tens of kilograms.

According to the researchers, the decrease in the size of game and the
need to hunt
small, swift animals forced humans to display cunning and boldness—an evolutionary
process that demanded increased volume of the human brain and later led to
the
development of language enabling the exchange of information about where prey could be found. The theory claims that all means served one end: body energy conservation.

The researchers show that, throughout most of their evolution, early
humans were
apex (top) predators, specializing in hunting large game. Representing
most of the
biomass available for hunting, these animals provided humans with high fat levels,
an essential source of energy, and enabled a higher energy return than
small game.
In the past, six different species of elephants lived in Africa,
comprising more than
half of the biomass of all herbivores hunted by humans. Initial evidence
from East
Africa indicates that homo sapiens only emerged in that area after a significant
decline in the number of elephant species in certain regions. Comparing
the size of
animals found in archaeological cultures, representing different species
of humans
in east Africa, southern Europe and Israel, the researchers found that in
all cases
there was a significant decline in the prevalence of animals weighing over 200kg,
coupled with an increase in the volume of the human brain.

"We correlate the increase in human brain volume with the need to become smarter hunters," explains Dr. Ben-Dor. For example, the need to hunt
dozens of gazelles
instead of one elephant generated prolonged evolutionary pressure on the
brain
functions of humans, who were now using up much more energy in both movement and thought processes. Hunting small animals, that are constantly
threatened by
predators and therefore very quick to take flight, requires a physiology adapted to
the chase as well as more sophisticated hunting tools. Cognitive activity
also rises as
fast tracking requires fast decision-making, based on phenomenal
acquaintance with
the animals' behavior—information that needs to be stored in a larger memory."
...

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