Climate has affected the size of human bodies and, to a lesser degree, human brains, a new study suggests.

An international and interdisciplinary team of researchers led by Manuel Will from the Department of Early Prehistory and Quaternary Ecology at the University of Tübingen in Germany, and colleagues from Cambridge, New Zealand and Canada, revealed new insights into human evolution and what drives it, published in the journal Nature Communications.

The researchers gathered data on body and brain size from over 300 fossils of the genus Homo found throughout the globe and coupled it with a reconstruction of the world's regional climates during the last million years.

They discovered that older, harsher climates fostered the evolution of bigger body sizes, whereas warmer climates drove the evolution of smaller bodies. Researchers discovered that, while brain size has changed considerably, it has not evolved in unison with body size.

"We found that different factors determine brain size and body size - they're not under the same evolutionary pressures," Will, the study's first author, said.

"The environment has a much greater influence on our body size than our brain size."

Non-environmental variables were also shown to be more significant than climate in driving bigger brains, with primary possibilities being the increased cognitive difficulties of increasingly complicated social lives, more diversified meals, and more sophisticated technologies.

According to researchers, the human body is still adjusting to varying temperatures, with larger-bodied people living in colder areas on average today.

The paper also mentions how brain size appears to be decreasing from the beginning of the Holocene (approximately 11,650 years ago), which is likely because of more reliance on technology. This is expected to continue as complex activities are outsourced to computers, which may cause brains to shrink even more over the next several thousand years.

Understanding how bodies and brains developed may give significant insight into the underlying pressures associated with human pathological changes, the authors said.