From Newsgroup: sci.anthropology.paleo


https://www.sciencedirect.com/science/article/pii/S0278262625000764

Highlights
rCo Human brain size expanded rapidly, then
plateaued over the past 300,000 years, with
significant glacialrCointerglacial differences
emerging in the last 100,000 years.

rCoLarge brains imposed costs that may have
heightened extinction risk, especially
during warming climates.

rCoCognitive tools and symbolic culture likely
reduced pressure for larger brains by
enabling cognitive offloading.

Abstract
Increasing brain size is a hallmark of human
evolution. While a larger brain offers
evolutionary advantages driven by social and
cognitive adaptations, it also imposes
considerable energetic, metabolic, and
thermoregulatory costs. As a result, brain
size may have biological limits that impose
survival pressures during periods of extreme
environmental change. Here, temporal trends
in absolute brain size across the genus Homo
are analyzed, with a focus on a marked
slowdown in growth beginning around 300,000
years ago. The results suggest that strong
directional selection for brain expansion in
early Homo was followed by a shift toward
stabilizing selection in later populations.
Comparisons across glacial and interglacial
periods indicate that the physiological costs
of large brains may have become especially
disadvantageous during warming interglacial
periods in the last 100,000 years,
potentially increasing extinction risk. This
evolutionary shift coincides with the
emergence of cognitive and cultural
innovations rCo such as symbolic tools and
language rCo that may have enabled cognitive
offloading, reducing selective pressure for
continued encephalization. Together, these
findings support the hypothesis that
stabilizing selection, mediated in part by
behavioral and technological adaptations,
buffered later Homo populations against the
ecological and physiological costs associated
with large brains.
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From Newsgroup: sci.anthropology.paleo

On 7/25/25 12:39 AM, Primum Sapienti wrote:

rCoLarge brains imposed costs that may have
heightened extinction risk, especially
during warming climates.

rCoCognitive tools and symbolic culture likely
reduced pressure for larger brains by
enabling cognitive offloading.

"Savanna" nonsense is just that; nonsense. The
savanna environment can't support the population
density of the forest. But, waterside, exploiting
marine resources beats the forest.

The point is that waterside ("Aquatic Ape")
could support the highest population density AND
the largest brains. We need DHA to build brains,
we are lousy at synthesizing it and without it
we can't have large brains. Period.

So, early one and for a VERY long time, groups
that exploited marine resources would have been
larger AND would have had virtually unlimited
supplies of DHA. But, it was the "Larger" that
counted.

They dominated.

THEN, with the advent of agriculture, suddenly
the inland groups could support the larger
population densities. And they didn't just have
the advantage of numbers, either! They could
feed animals with their surplus. They could
trade. They could specialize, support craftsmen
and artisans with their surplus... They had
disadvantages, yes, but the advantages squashed
the disadvantages.

One disadvantage was a diet far weaker in DHA.

EVEN TODAY, RIGHT NOW most people are NOT getting
enough DHA in their diets.

A lot of times things like milk will get
supplemented, "Fortified" with DHA, just to increase
what people are getting. And of course we can
synthesize it, just not very well, and between the
two most people still fall short of the recommended
intake of DHA.

Again: No DHA, no growing big brains!
--
https://jtem.tumblr.com/tagged/The%20Book%20of%20JTEM/page/5
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