Modern humans have brains that are more than three times larger than our closest living relatives, chimpanzees and bonobos. Scientists don’t agree on when and how this dramatic increase took place, but new analysis of 94 hominin fossils shows that average brain size increased gradually and consistently over the past three million years.
The research, published this week in the Proceedings of the Royal Society B, shows that the trend was caused primarily by evolution of larger brains within populations of individual species, but the introduction of new, larger-brained species and extinction of smaller-brained ones also played a part.
“Brain size is one of the most obvious traits that makes us human. It’s related to cultural complexity, language, tool making and all these other things that make us unique,” said Andrew Du, PhD, a postdoctoral scholar at the University of Chicago and first author of the study. “The earliest hominins had brain sizes like chimpanzees, and they have increased dramatically since then. So, it’s important to understand how we got here.”
Du began the work as a graduate student at the George Washington University (GW). His advisor, Bernard Wood, GW’s University Professor of Human Origins and senior author of the study, gave his students an open-ended assignment to understand how brain size evolved through time. Du and his fellow students, who are also co-authors on the paper, continued working on this question during his time at George Washington, forming the basis of the new study. Continue reading