How climate changed the evolution of the human body

A team of scientists led by the University of Cambridge has investigated how the evolution of human bodies and brains may relate to climate, which generally affects the body size of animals. 

Sure, there are mice in Alaska and elephants in tropical Africa, but colder climates tend to favor larger body sizes while warmer climates push animals to evolve smaller sizes. 

As the mass of a body increases, its surface area increases at a slower rate. This means that larger bodies are thought to lose less heat than smaller ones. Conversely, larger bodied animals tend to overheat more easily, and humans are no exception to this rule. 

The study revealed that the human body size has fluctuated quite a bit over the last million years, with larger bodied humans evolving in colder climates. 

Our species, Homo sapiens, is larger bodied and bigger brained than some of our possible ancestors such as Homo habilis. There is much debate over what drove the evolution of larger brains and bodies in humans, and climate could be one of the driving factors. 

Interestingly, it does not seem that brain size is correlated to changes in climate like body size. Instead, different factors are at play. 

While it is possible that social life may have driven the growth in brain size, it is also related to ecology in a roundabout way. Members of our genus living in open areas such as grasslands tended to have bigger brains, the researchers found, which was possibly due to social hunting of large animals in such habitats. 

“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 study first author Dr.  Manuel Will at the University of Tubingen.

“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.”

The scientists caution on reading too much into their research, so many factors were involved in our evolution and those factors aren’t necessarily the same today as they were. 

The study is published in the journal Nature Communications.

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By Zach Fitzner, Earth.com Staff Writer