Climate changed the size of our bodies and, to some extent, our brains


Date:
July 8, 2021
Source:
University of Cambridge
Summary:
The average body size of humans has fluctuated significantly
over the last million years and is strongly linked to
temperature. Colder, harsher climates drove the evolution of larger
body sizes, while warmer climates led to smaller bodies. Brain
size also changed dramatically but did not evolve in tandem with
body size.



FULL STORY ==========================================================================
An interdisciplinary team of researchers, led by the Universities of
Cambridge and Tu"bingen, has gathered measurements of body and brain
size for over 300 fossils from the genus Homo found across the globe. By combining this data with a reconstruction of the world's regional climates
over the last million years, they have pinpointed the specific climate experienced by each fossil when it was a living human.


==========================================================================
The study reveals that the average body size of humans has fluctuated significantly over the last million years, with larger bodies evolving
in colder regions. Larger size is thought to act as a buffer against
colder temperatures: less heat is lost from a body when its mass is
large relative to its surface area. The results are published today in
the journal Nature Communications.

Our species, Homo sapiens, emerged around 300,000 years ago in Africa. The genus Homo has existed for much longer, and includes the Neanderthals
and other extinct, related species such as Homo habilis and Homo erectus.

A defining trait of the evolution of our genus is a trend of increasing
body and brain size; compared to earlier species such as Homo habilis,
we are 50% heavier and our brains are three times larger. But the drivers behind such changes remain highly debated.

"Our study indicates that climate -- particularly temperature -- has been
the main driver of changes in body size for the past million years," said Professor Andrea Manica, a researcher in the University of Cambridge's Department of Zoology who led the study.

He added: "We can see from people living today that those in warmer
climates tend to be smaller, and those living in colder climates tend
to be bigger. We now know that the same climatic influences have been
at work for the last million years." The researchers also looked at
the effect of environmental factors on brain size in the genus Homo,
but correlations were generally weak. Brain size tended to be larger when
Homo was living in habitats with less vegetation, like open steppes and grasslands, but also in ecologically more stable areas. In combination
with archaeological data, the results suggest that people living in these habitats hunted large animals as food -- a complex task that might have
driven the evolution of larger brains.

"We found that different factors determine brain size and body size --
they're not under the same evolutionary pressures. The environment has
a much greater influence on our body size than our brain size," said
Dr Manuel Will at the University of Tubingen, Germany, first author of
the study.

He added: "There is an indirect environmental influence on brain size
in more stable and open areas: the amount of nutrients gained from the environment had to be sufficient to allow for the maintenance and growth
of our large and particularly energy-demanding brains." This research
also suggests that non-environmental factors were more important for
driving larger brains than climate, prime candidates being the added
cognitive challenges of increasingly complex social lives, more diverse
diets, and more sophisticated technology.

The researchers say there is good evidence that human body and brain size continue to evolve. The human physique is still adapting to different temperatures, with on average larger-bodied people living in colder
climates today. Brain size in our species appears to have been shrinking
since the beginning of the Holocene (around 11,650 years ago). The
increasing dependence on technology, such as an outsourcing of complex
tasks to computers, may cause brains to shrink even more over the next
few thousand years.

"It's fun to speculate about what will happen to body and brain sizes in
the future, but we should be careful not to extrapolate too much based on
the last million years because so many factors can change," said Manica.

========================================================================== Story Source: Materials provided by University_of_Cambridge. The original
story is licensed under a Creative_Commons_License. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Manuel Will, Mario Krapp, Jay T. Stock, Andrea Manica. Different
environmental variables predict body and brain size evolution
in Homo.

Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-24290-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210708083900.htm

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