The research, published in the Proceedings of the National Academy of Sciences (PNAS) on November 26, presents evidence that brain size increased steadily within individual species over millions of years, rather than through dramatic shifts between species. The study, led by researchers from the University of Reading, University of Oxford, and Durham University, provides a detailed analysis of brain evolution using the most extensive dataset of ancient human fossils to date.
Using advanced computational and statistical techniques to fill gaps in the fossil record, the team reconstructed brain size evolution across a 7-million-year timespan. The findings depict a gradual, continuous increase in brain size within species, debunking earlier ideas of abrupt evolutionary leaps.
"This study completely changes our understanding of how human brains evolved," said Professor Chris Venditti from the University of Reading. "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 results also challenge assumptions that certain species, like Neanderthals, were static and unchanging. Instead, the researchers emphasize that gradual evolutionary adaptations played a central role in driving changes in brain size.
"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," explained Dr. Thomas Puschel, the study's lead author, now based at the University of Oxford.
Brains, bodies, and evolutionary complexity
The research highlighted that while larger-bodied species generally had bigger brains, brain size evolution across long timescales did not align neatly with body size within individual species. This finding underscores the complexity of evolutionary pressures influencing brain size.
Dr. Joanna Baker, a co-author from the University of Reading, remarked: "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 project, supported by a GBP 1 million Research Leadership Awards grant from the Leverhulme Trust, offers a deeper understanding of human evolutionary history and the development of large brains among our ancestors.
Research Report:Hominin brain size increase has emerged from within-species encephalization
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