Our bigger brains may have led to bigger bodies. Scientists found that humans primarily became larger due to increases in our brain size.
"Over the last four million years, brain size and body size increased substantially in our human ancestors," said Mark Grabowski, one of the researchers involved in the new study and a James Arthur postdoctoral fellow in the Division of Anthropology at the American Museum of Natural History. "This observation has led to numerous hypotheses attempting to explain why observed changes occurred, but these typically make the assumption that brain- and body-size evolution are the products of separate natural selection forces."
Now, though, this assumption is being questioned by researchers. Scientists recently conducted a large body of work that shows that genetic variation in some traits is due to genes that also cause variation in other traits, with the result that selection on either trait leads to a correlated response in the unselected trait. For example, as a leg bone in an elephant becomes longer, the bone also gets wider. This is due to shared genetic variation.
In this latest study, researchers wanted to see whether there was a genetic relationship between human brain size and human body size. The scientists created a number of models in order to examine how underlying genetic relationships and selection pressures likely interacted across the evolution of humans.
So what did they find? It turns out that strong selection to increase brain size alone played a large role in both brain and body size increases throughout the course of human evolution. In fact, this could have been solely responsible for the major increase in both traits that occurred during the transition from human ancestors to actual humans.
"While selection no doubt played a role in refining the physical changes that came with larger body sizes, my findings suggest it was not the driving force behind body-size evolution in our lineage," Grabowski said. "Therefore, evolutionary models for the origins of Homo based on an adaptive increase in body size need to be reconsidered."
The findings reveal a bit more about human evolution. This, in turn, may reveal why our ancient, human-like ancestors changed the way they did.
The findings were published in the April edition of the journal Current Anthropology.
