When and Why Did Human Brains Decrease in Size? A New Change-Point
Analysis and Insights From Brain Evolution in Ants.
Human brain size nearly quadrupled in the six million years since Homo
last shared a common ancestor with chimpanzees, but human brains are
thought to have decreased in volume since the end of the last Ice Age.
The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced
positive rate changes at 2.1 and 1.5 million years ago, coincident
with the early evolution of Homo and technological innovations evident
in the archeological record. But we also find that human brain size
reduction was surprisingly recent, occurring in the last 3,000 years.
Our dating does not support hypotheses concerning brain size reduction
as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest
our analysis supports the hypothesis that the recent decrease in brain
size may instead result from the externalization of knowledge and
advantages of group-level decision-making due in part to the advent of
social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains
contribute to the emergence of collective intelligence. Although
difficult to study in the deep history of Homo, the impacts of group
size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as
models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of
labor, and collective cognition. Ants provide a wide range of social
systems to generate and test hypotheses concerning brain size
enlargement or reduction and aid in interpreting patterns of brain
evolution identified in humans. Although humans and ants represent
very different routes in social and cognitive evolution, the insights
ants offer can broadly inform us of the selective forces that
influence brain size. https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full
When and Why Did Human Brains Decrease in Size? A New Change-PointThanks Pandora, interesting comparison.
Analysis and Insights From Brain Evolution in Ants.
Abstract
Human brain size nearly quadrupled in the six million years since Homo
last shared a common ancestor with chimpanzees, but human brains are
thought to have decreased in volume since the end of the last Ice Age.
The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced
positive rate changes at 2.1 and 1.5 million years ago, coincident
with the early evolution of Homo and technological innovations evident
in the archeological record. But we also find that human brain size
reduction was surprisingly recent, occurring in the last 3,000 years.
Our dating does not support hypotheses concerning brain size reduction
as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest
our analysis supports the hypothesis that the recent decrease in brain
size may instead result from the externalization of knowledge and
advantages of group-level decision-making due in part to the advent of
social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains
contribute to the emergence of collective intelligence. Although
difficult to study in the deep history of Homo, the impacts of group
size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as
models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of
labor, and collective cognition. Ants provide a wide range of social
systems to generate and test hypotheses concerning brain size
enlargement or reduction and aid in interpreting patterns of brain
evolution identified in humans. Although humans and ants represent
very different routes in social and cognitive evolution, the insights
ants offer can broadly inform us of the selective forces that
influence brain size.
Open access: https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full
When and Why Did Human Brains Decrease in Size? A New Change-Point
Analysis and Insights From Brain Evolution in Ants.
https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full
Although humans and ants represent very different routes in
social and cognitive evolution, the insights ants offer can broadly
inform us of the selective forces that influence brain size.
On Wednesday, October 27, 2021 at 5:54:09 PM UTC+1, Pandora wrote:No, just a discourse three levels above your mental acuity.
When and Why Did Human Brains Decrease in Size? A New Change-PointAn entry for the Ig Nobels?
Analysis and Insights From Brain Evolution in Ants. https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full
Although humans and ants represent very different routes in
social and cognitive evolution, the insights ants offer can broadly
inform us of the selective forces that influence brain size.
An explanation based on simple mechanics willYou confuse effects of social organization with effects of biological organization.
always be more parsimonious.
Take a look at human ancestral hair: i.e. that of
peoples native to tropics.
would not be present if it wasn't needed.
what's the need? It's not protection against
heat -- humans can usually find shade during the
day, and no other tropical species have anything
like it. Nor is there substantial evidence that
humans are (or ever have been) selected against
as the result of exposure to heat.
But humans who have to go into cold waters to
fish, or travel across dangerous water channels
do drown. Often hypothermia, affecting the
brain, is the cause or a major contributory
factor. Insulation that can reduce the incidence
will be selected for.
That brain insulation takes two forms: larger
brains, and dense, extensive head hair.
When the pressure of that selection eases, as
when the bulk of the population ceases to fish in
cold waters, or travels less (or with less risk) over
such waters, or stops living on coasts exposed to
occasional tsunamis, selective pressures will
decline and the substantial costs involved will
ensure that brain size declines.
We can see this in most human populations over
the last few thousand years. This conclusion is
reinforced by the example of h.naledi -- a
population we can assume was never close to
the sea, and rarely exposed to the night cold
outside its caves.
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