Human chromosomes evolved at hyperspeed to give us better brains, but there’s a catch microbiologystudy

How did humans evolve brains capable of complex language, civilization, and more? The answer could lie in exceptional DNA. Scientists at UC San Francisco have found that parts of our chromosomes have evolved at breakneck speeds to give us an edge in brain development compared to apes. But it might also put us at risk for uniquely human brain disorders.

The study appears 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, Ph.D., 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.

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, 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.”