Brains grew faster as humans evolved, study shows

Modern humans, Neanderthals, and other recent relatives on our human family tree evolved bigger brains much more rapidly than earlier species, a new study of human brain evolution has found. 

The study, published today (Tuesday, 26 November) in the journal PNAS, overturns long-standing ideas about human brain evolution. Scientists from the University of Reading, the University of Oxford and Durham University found that brain size increased gradually within each ancient human species rather than through sudden leaps between species.

The team assembled the largest-ever dataset of ancient human fossils spanning 7 million years and used advanced computational and statistical methods to account for gaps in the fossil record. These innovative approaches provided the most comprehensive view yet of how brain size evolved over time.

Professor Chris Venditti, co-author of the study from the University of Reading, said: "This study completely changes our understanding of how human brains evolved. It was previously thought that brain size jumps dramatically between species, like new upgrades between the latest computer models. Our study instead shows a steady, incremental ‘software update’ happening within each species over millions of years.”

The research challenges old ideas that some species, like Neanderthals, were unchanging and unable to adapt and instead highlights gradual and continuous change as the driving force behind brain size evolution.

Dr Thomas Puschel, lead author now at Oxford University, said: “Big evolutionary changes don’t always need dramatic events. They can happen through small, gradual improvements over time, much like how we learn and adapt today.”

Brains, bodies, and evolutionary scale

The researchers also uncovered a striking pattern: while larger-bodied species generally had bigger brains, the variation observed within an individual species did not consistently correlate with body size. Brain size evolution across long evolutionary timescales extending millions of years is therefore shaped by different factors to those observed within individual species – highlighting the complexity of evolutionary pressures on brain size. 

Dr Joanna Baker, co-author from the University of Reading, said: “Why and how humans evolved large brains is a central question in human evolution. By studying brain and body size in  various species over millions of years, we reveal that our hallmark large brains arose primarily from gradual changes within individual species.”

The study was produced as part of a £1 million Research Leadership Awards grant from the Leverhulme Trust. The project was to better understand the evolution of human ancestors. 

Püschel, T. A., Nicholson, S. L., Baker, J., Barton, R. A., & Venditti, C. (2024). Hominin brain size increase has emerged from within-species encephalization. Proceedings of the National Academy of Sciences, 121(49), e2409542121. https://doi.org/10.1073/pnas.2409542121

 Image via Flickr user _DJ_.