The relationship between cranial capacity, body size, and time both within- and between-species.
Credit: Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2409542121
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.
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 research, published November 26 in the Proceedings of the National Academy of Sciences, overturns long-standing ideas about human brain evolution.
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."
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