Ancient Retrovirus Explains Human-Chimpanzee Brain Divergence

Viral Impact on Brain Evolution

A recent study indicates that a virus, PTERV1, which infected chimpanzees millions of years ago, played a role in the evolutionary divergence of human and chimpanzee brain development. This divergence may contribute to the greater cognitive complexity observed in humans compared to their closest living relatives.

Retroviruses like PTERV1 can insert their genetic material into host genomes, leading to long-term evolutionary effects. Researchers found that PTERV1 is abundant in chimpanzees but absent in humans, and it influences brain development.

Human Brain Uniqueness

The human brain is notably larger and more complex than other primate brains, partly due to an increased number of cortical neurons and enhanced synaptic connectivity. This results in unique cognitive capabilities, with the human brain being roughly three times the size of a chimpanzee's.

The genetic differences underlying these distinctions have been largely unclear. The new findings propose a mechanism where endogenous retroviral insertions contributed to the divergence in brain development between humans and chimpanzees.

Mechanism of Divergence

The research team utilized human and chimpanzee brain organoids, which are miniature neuron clusters grown from stem cells, to model aspects of brain development. Their findings revealed that chimpanzee-specific PTERV1 insertions on chromosome 19 silence a gene called LINC00662.

In contrast, the LINC00662 gene remains active during human brain development. This gene is known to affect neuronal maturation, development, and outgrowth, suggesting its role in the distinct developmental paths of human and chimpanzee brains.

PTERV1 elements are believed to have originated from infections in the ancestors of African apes approximately 5 to 7 million years ago, and are present in chimpanzees, bonobos, and gorillas.