An interdisciplinary team of researchers led by the Universities of Cambridge and Tubingen acquired over 300 fossils from the species Homo to estimate body and brain size.
They pinpointed the precise environment experienced by each fossil when it was a living human by integrating this data with a simulation of the world’s regional climates during the last million years.
Our species, Homo sapiens, first appeared in Africa some 300,000 years ago. The Neanderthals and other extinct, related species such as Homo habilis and Homo erectus belong to the genus Homo, which has been around for considerably longer.
The findings show that human body size has changed dramatically over the last million years, with larger bodies emerging in colder climates.
The larger size is supposed to act as a buffer against cooler temperatures: when a body’s mass is large compared to its surface area, less heat is lost. The findings were just published in the journal Nature Communications.
The tendency of rising body and brain size has been a defining feature of our genus’ history; we are 50 percent heavier and our brains are three times larger than earlier species like Homo habilis. However, the causes of such shifts are hotly contested.
“For the past million years, climate – notably temperature – has been the main driver of changes in body size,” said Professor Andrea Manica, the study’s lead author and a researcher at the University of Cambridge’s Department of Zoology.
“We can observe from today’s population that those who live in warmer climates are smaller, and those who live in colder climes are larger,” he continued. We now know that throughout the last million years, the same climatic influences have been at work.”
The researchers also looked at the impact of environmental influences on brain size in Homo sapiens but found few relationships. When Homo sapiens lived in settings with less vegetation, such as open steppes and grasslands, but also ecologically more stable locations, their brains were larger.
The findings, when combined with archaeological evidence, show that people living in these ecosystems hunted enormous animals for food, a difficult undertaking that may have prompted the evolution of larger brains.
“We discovered that brain and body size are determined by separate variables and that they are not subject to the same evolutionary pressures.”
The environment has a lot higher impact on our bodily size than it does on our brain size,” stated the study’s first author, Dr. Manuel Will of the University of Tubingen in Germany.
“In more stable and open locations, there is an indirect environmental influence on brain size: the number of nutrients obtained from the environment had to be sufficient to allow for the preservation and growth of our huge and very energy-demanding brains,” he continued.
Non-environmental variables, rather than climate, appear to be more crucial in promoting larger brains, with the extra cognitive challenges of increasingly complicated social lives, more diverse foods, and more sophisticated technologies being obvious candidates.
According to the researchers, there is strong evidence that the human body and brain are still evolving. The human body is still adjusting to various temperatures, with larger-bodied people living in colder areas on average nowadays.
Since the beginning of the Holocene, our species’ brain size appears to have shrunk (around 11,650 years ago).
Over the next few thousand years, increased reliance on technology, such as outsourcing hard activities to computers, may cause brains to shrink even more.
“It’s exciting to guess about what may happen to body and brain sizes in the future,” Manica said. “However, we ought to be cautious about extrapolating too much from the last millions of years because many elements may change.”