Ancient Viral DNA May Have Curbed Chimpanzee Brain Evolution

WHO:

ScienceAlert - Lead author Patricia Gerdes is a molecular neurogeneticist at Lund University in Sweden.

ScienceAlert - The study concerns humans, chimpanzees (*Pan troglodytes*), and other African apes.

Phys.org - Researchers at Lund University in Sweden reported that an ancient viral pandemic is likely part of the explanation for differences in human and chimpanzee brain development.

WHAT:

ScienceAlert - Humans and chimpanzees differ in about 1.2 percent of their DNA after evolving from a common ancestor for about 5–6 million years; human brains are about three times larger than chimpanzee brains.

ScienceAlert - The study found that PTERV1 (Pan troglodytes endogenous retrovirus-1), present in chimpanzees and other African apes but not humans, inserted DNA into the chimpanzee genome and switches off the gene LINC00662.

ScienceAlert - Humans and chimpanzees both have LINC00662. Gerdes said it is active during early human brain development, and experiments suggest it helps human brain cells mature and grow extensions.

ScienceAlert - In human brain organoids, switching off LINC00662 reduced the maturation and growth of neurons and their dendrites and axons.

ScienceAlert - Removing the viral insertion from chimpanzee stem cells restored LINC00662 activity. Gerdes said this shows the insertion contributes to switching off the gene, but does not show that removing it would transform brain development.

ScienceAlert - Gerdes said researchers cannot predict that the same insertion in humans would produce a particular brain shape, ability, or behavior; effects could depend on surrounding human DNA and other genes.

ScienceAlert - Gerdes said removing the insertion from an adult brain would not undo earlier brain development.

Phys.org - Researchers reported that a viral pandemic dating back several million years is likely part of the explanation for differences in how human and chimpanzee brains developed.

WHERE:

ScienceAlert - The research was conducted by a team whose lead author is at Lund University in Sweden; experiments used human brain organoids and chimpanzee stem cells.

WHEN:

ScienceAlert - The PTERV1 infection occurred about 4 million years ago; the article says the research was published in *Science Advances*.

WHY:

ScienceAlert - The study investigated how human and chimpanzee brains could have evolved differently despite similarities in their protein-making genes.

ScienceAlert - The researchers said it remains unclear why humans did not contract PTERV1. Possible explanations offered by Gerdes included protection by the antiviral protein TRIM5α or different locations of chimpanzee and human ancestors when the viral pandemic occurred.

HOW:

ScienceAlert - The virus’s DNA insertion affects LINC00662 in chimpanzees; experiments used brain organoids to test the gene’s effects and chimpanzee stem cells to assess the insertion’s role.

ScienceAlert - Gerdes said researchers do not yet know all the roles of LINC00662 in the human body or what loss of its activity means for chimpanzees as a whole.

(UPDATED October 23, 2026 23:21 UTC)

An ancient viral infection may help explain why human and chimpanzee brains developed differently, according to researchers at Lund University in Sweden. Humans and chimpanzees share a common ancestor, but human brains are about three times larger. The study found that PTERV1, a virus that infected African apes about 4 million years ago, left DNA in chimpanzees but not humans. That insertion switches off LINC00662, a gene found in both species. Lead author Patricia Gerdes says the gene is active during early human brain development and may help brain cells mature and grow extensions. In human brain organoids, switching off the gene reduced neuron development. Removing the viral insertion from chimpanzee stem cells restored gene activity, but researchers caution this does not show that brain development would change. The study also cannot explain why humans avoided the virus or predict effects on behavior.