Climate affects body and brain size. That's the discovery of researchers who combined data on fossils with climate change.
Current humans are much larger and have brains three times larger than previous Homo species that lived millions of years ago. A research team led by the University of Cambridge and the University of Tübingen in Germany combined data on more than 300 human fossils with climate models to determine the role climate played on evolution. The study was published in Nature Communication and revealed that there is a strong link between the temperature of the environment and the body size of humans.
Research into the effects of climate on the evolution of the human body
Scientists determined what temperatures, precipitation and weather conditions there were at the time the human fossils found over the past million years lived. The results showed that climate was a key factor in body size. "The colder it gets, the bigger the humans are," said Manuel Will, a researcher at the University of Tübingen and one of the study's first authors.
"If you have a bigger body, you produce more heat but dissipate relatively less because your surface area doesn't expand at the same rate," Will explained. The relationship between climate and body mass would be consistent with Bergmann's rule of higher body weight in colder environments and lower body weight in warmer environments. This condition is observed in animal species such as bears: for example, polar bears living in the Arctic weigh significantly more than brown bears living in relatively warmer climates.
The study also found a link between brain size and climate, but the results show that environmental factors have substantially less influence on brain size than body size. Andrea Manica, another researcher in the study explained that this phenomenon "shows how body and brain size depend on different selective conditions."
While there is no association between brain size and temperature from the results, the researchers did find a link between more stable climate and larger brain size. This effect would be caused by the diet of humans living in environments of varying climate stability.
"You need a lot of energy to maintain a large brain," Will pointed out, "in stable environments you probably have enough nutrition to give you that energy. The researchers went on to note how behavioral changes that affect brain size are a response to different hunting strategies. The conclusion, then, is that there are also other competitive, social, cultural and technological factors that were not tested in the study, but along with climate affect human evolution. For this reason, there is no certainty that the overheating of the Earth, caused by climate change, can lead the bodies of humans to become smaller.
If even our size does not shrink, air pollution is creating significant problems for the globe starting with oxygen that is disappearing from freshwater lakes.