Fast-evolving DNA gives human neurons greater complexity than chimps, aiding cognition but also increasing disease risk.

A study of artificial human and chimpanzee nerve cells revealed how faster-evolving DNA enables neurons to develop increasingly complex brain power.

How did humans evolve brains capable of complex language, civilization, and more?

The answer may lie in exceptional DNA. Scientists at UC San Francisco discovered that certain regions of our chromosomes have evolved at remarkable speeds, giving us an advantage in brain development over apes. However, this rapid evolution may also make us more susceptible to uniquely human brain disorders.

The study, which was supported by grants from the National Institutes of Health, was recently published in Nature.

The research focused on parts of chromosomes known as human accelerated regions (HARs), which have evolved most rapidly since humans split from chimpanzees on the evolutionary tree – changing 10 times faster than the expected rate of evolution in mammals.

The scientists, led by Yin Shen, PhD, professor in the UCSF Weill Institute for Neurosciences and the UCSF Institute for Human Genetics, studied the effects of HARs in artificial neurons derived from human and chimpanzee cell lines.

How HARs Influence Brain Development

The human and chimpanzee genomes are 99% similar. HARs make up a big portion of the 1% difference, which can lead to dramatically different outcomes in human and chimp neurons in petri dishes. The human neurons grew multiple neurites, or wiry projections that help the nerve cells send and receive signals. But the chimp neurons only grew single neurites. When human HARs were engineered into artificial chimp neurons, the chimp neurons grew many more of these wires.

“More neurites during development could mean more complexity in our neural networks,” Shen said. “These networks facilitate the transmission of signals in the nervous system and support our higher cognitive functions. But disruptions in their development may contribute to neurodevelopmental disorders like autism.”

Reference: “Comparative characterization of human accelerated regions in neurons” by Xiekui Cui, Han Yang, Charles Cai, Cooper Beaman, Xiaoyu Yang, Hongjiang Liu, Xingjie Ren, Zachary Amador, Ian R. Jones, Kathleen C. Keough, Meng Zhang, Tyler Fair, Armen Abnousi, Shreya Mishra, Zhen Ye, Ming Hu, Alex A. Pollen, Katherine S. Pollard and Yin Shen, 26 February 2025, Nature.
DOI: 10.1038/s41586-025-08622-x

Funding: This work was supported by the US National Institutes of Health (NIH) grants U01DA052713, UM1HG009402, R21DA056293, R21HG010065, R01MH109907, U01MH116438, DP2MH122400-01, P30DK063720, and S101S10OD021822-01; the Schmidt Futures Foundation; the Chan Zuckerberg Biohub; and the Gladstone Institutes.