Climate change altered the size of human bodies

(CNN) – The average size of human bodies has fluctuated significantly over the past million years and is linked to changing weather, according to research published Thursday.

A team of researchers led by the University of Cambridge in the United Kingdom and the University of Tübingen in Germany collected measurements of brain and body size from more than 300 fossils of the genus or family. Homo, to which modern humans belong, Homo sapiens.

The team used this data in combination with a reconstruction of the climates in different regions of the Earth over the past million years, and calculated what the climate would be like experienced by each fossil when it was a living human being.

The researchers found that climate, particularly temperature, has been the main driver of changes in body size in the last few million years. Colder, harsher climates could be associated with larger bodies, while warmer climates, with smaller bodies, the team discovered.

“Larger bodies can protect people from cold temperatures. The bigger you are, the smaller your surface area compared to your volume, so you conserve heat more efficiently,” Andrea Manica, professor, told CNN. of Evolutionary Ecology at the University of Cambridge.

“This is a relationship that is found in many animals, and even among contemporary humans, but we now know that it was one of the main drivers of changes in body size in the last few million years,” he explained.

The research was published in the journal Nature Communications.

The links between climate and brain size are not so clear

The researchers also looked at the impact of environmental factors on brain size.

The Homo sapiens arose about 300,000 years ago in Africa, but the genus Homo, which includes Neanderthals and other related extinct species such as the Homo habilis and the Homo erectus, has been around for much longer.

Experts said that compared to earlier species like Homo habilis, we, the Homo sapiens, we are 50% heavier and our brains are three times bigger. However, there is still a debate about the reasons behind the change.

The team found that weather did play a role in brain size, but that there was so much variation in size that it couldn’t be explained by environmental changes.

“Interestingly, changes in brain size were not related to temperature at all, so body and brain sizes evolved under different pressures,” Manica explained.

“In terms of brain size, we found that the largest brains were in stable environments. Brains are expensive, so you can’t maintain them if you lack resources,” he explained.

He also added that, in the case of the first Homo, “There was also a tendency to develop larger brains in more open habitats, where our ancestors would have had to hunt large mammals.”

“However, it is important that climate explains much less changes in brain size than body size. This means that other factors are likely to have been the main drivers of changes in brain size, such as additional cognitive challenges from increasingly complex social lives, more diverse diets and more sophisticated technologies, “he added.

What could happen to the size of our bodies with the current climate change?

Manica believes that current climate change is unlikely to drastically impact our bodies at the moment.

“The changes we describe occurred over periods of thousands of years, or rather tens of thousands of years,” he explained. “So a few years of climate change will affect our bodies or brains little,” he added.

“If we could keep changing the climate without destroying the entire planet for a long period of time – we’re not doing very well in that regard – then maybe (there would be changes in body size), but fortunately this is a matter of the that we don’t have to worry for quite some time, “he said.

Higher temperatures are affecting animals

Still, climate change may already be shrinking some of the animalss of the planet.

In the last four decades, migratory birds of North America They have gotten smaller and their wingspan larger. The changes appear to be a response to warmer weather, according to a 2019 study.

In an analysis of 70,716 dead birds representative of 52 species recorded between 1978 and 2016, the researchers found that 49 had statistically significant decreases in body size.

Impact on cold-blooded animals

The authors suggested that the reduction in body size is a response to rising temperatures, as temperatures in the birds’ summer breeding grounds north of Chicago increased by about 1 degree Celsius over the course of the study.

What’s more, a 2011 study published in the journal Nature Climate Change found that ectotherms – cold-blooded animals like toads, turtles and snakes, which depend on heat from environmental sources – “are already changing a lot” as temperatures rise.

Both aquatic and terrestrial ectotherms have been shrinking, according to the study. The size and condition of the common toads have declined as temperatures rose 1.5 degrees Celsius over a 22-year period.