Researchers led by the University of Cambridge and Tübingen published a new study that looks at the changing climate and how it impacted the body size of Homo sapiens and our ancient ancestors. Researchers gathered measurements from brain and body size of over 300 fossils from the genus Homo that have been discovered across the globe. Combining data on the body and brain size of ancient humans along with reconstructing the world’s regional climates over the last million years, scientists say they have pinpointed specific climates experienced by each fossil while it was living.
The study has found that the average body size of humans has fluctuated significantly across the last million years. In colder regions, larger bodies evolved with the thought that larger body size acts as a buffer against colder temperatures. Less heat would be lost from a larger body relative to its surface area. The species Homo sapiens emerged about 300,000 years ago, but the genus Homo existed for much longer and included Neanderthals and other extinct species related to modern humans, including Homo habilis and Homo erectus.
One defining characteristic of the evolution of the genus Homo is a trend of increasing body and brain size compared to past species. Researchers point to Homo habilis, compared to that ancient relative modern humans are 50 percent heavier, and our brains are three times larger. Exactly what drove these changes is a subject of debate among scientific circles. The new study indicates that climate and, in particular, the temperature has been the main driver of changes in body size for the past million years.
Researchers note that this still holds today, with people living in colder climates tending to be bigger. Researchers searched for environmental factors that impact brain size and the genus Homo but found correlations were generally weak. Brain size tended to be larger when the genus was living in habitats with less vegetation, such as open steps in grasslands and more ecologically stable areas. The study looked at archaeological data with results suggesting people who lived in those habitats hunted large animals as food which was a complex task requiring the evolution of larger brains.
The study has determined that while the climate impacts body size, non-environmental factors are more important for driving larger brains than the climate. The prime indicators for brain growth, according to the study, are added cognitive challenges of complex social lives, more diverse diets, and more sophisticated technology.