A team of researchers led by the University of Cambridge (United Kingdom) and the University of Tübingen (Germany) has compiled measurements of the size of the brain and the body of more than 300 fossils of the genus or family Homo, to which modern humans, Homo sapiens, they belong. The experts used this data, combined with a reconstruction of Earth’s regional climates from the last million years, and calculated the climate that each fossil would have experienced when it was a living human being.
The results were clear: Climate, particularly temperature, has been the main driver of changes in body size for the past few million years. Colder and harsher climates resulted in larger bodies, while warmer climates were associated with smaller bodies. It is believed that a larger body size would act as a buffer against colder temperatures, since less heat is lost when its mass is large in relation to its surface area.
Our species, Homo sapiens , emerged about 300,000 years ago in Africa (although the genus Homo has been around much longer and includes Neanderthals and other related extinct species, such as Homo habilis and Homo erectus) .
Compared to previous species like Homo habilis, we weigh 50% more and our brains are three times larger. But the factors that have triggered these changes have been the subject of intense debate.
“Our study indicates that climate, particularly temperature, has been the main driver of changes in body size over the past million years,” explains Andrea Manica, a researcher at the Department of Zoology at the University of Cambridge who led the study. “We can see in humans that currently live in warmer climates tend to be smaller and those that live in colder climates tend to be larger. We now know that the same climatic influences have been operating for the last million years, ”he continues.
And the brain?
The researchers also found that brain size tended to be larger when humans lived in less vegetated habitats, such as open steppes and grasslands, but also in more ecologically stable areas. Combined with available archaeological data, the results suggest that those who lived in these habitats hunted large animals for food, a complex task that could have driven the evolution of larger brains .
“We discovered that different factors determine brain size and body size; they are not under the same evolutionary pressures. The environment has a much greater influence on the size of our body than the size of our brain. “
Thus, “curiously, changes in brain size were not related to temperature at all, so body and brain size evolved under different pressures,” Manica said.
What effect can this finding have on us? Will climate change affect us?
According to the authors, “the changes we describe have occurred over thousands of years, or rather, tens of thousands of years, so a few years of climate change will have little effect on our bodies or brains .” However, it is affecting animals and nature in general. As an example, note that the migratory birds of North America have become smaller during the last four decades and their wingspan is wider; changes that seem to be the answer to a warmer climate.
Referencia: Nature Communications (2021). DOI: 10.1038/s41467-021-24290-7
