# Ancient Retroviral Insertions Influenced Human Brain Evolution Viral DNA remnants in chimpanzee genomes reveal mechanisms behind human brain development divergence. - **Source:** [Sci.News: Breaking Science News](https://www.sci.news/) - **Published:** 2026-10-28 - **Original article:** - **On Brifing:** https://brifing.si/s/5c82b486-7b83-4a58-9a64-e97c026949b1 ## Evolutionary Divergence Mechanisms Humans and chimpanzees share over 96% of protein-coding DNA, yet human brains are significantly larger and more complex. Research led by Lund University suggests that ancient viral infections in chimpanzee ancestors created genetic differences. These retroviral insertions, absent in humans, potentially altered gene regulation pathways during critical stages of primate brain development. ## The PTERV1 Viral Impact The study focuses on PTERV1, a retrovirus that invaded the germ line of African ape ancestors roughly 5 to 7 million years ago. While the human genome contains no PTERV1 insertions, the chimpanzee genome carries at least 150. This specific viral presence marks a distinct genetic divergence between the two species. ## Neural Organoid Methodology Researchers grew neural organoids from human and chimpanzee stem cells to observe developmental differences. Using long-read DNA sequencing, they identified that PTERV1 insertions in chimpanzees were heavily tagged with methyl groups. This chemical tagging is a known mechanism for gene silencing, which prevents the expression of specific genetic sequences during development. ## LINC00662 Gene Activity The study identified LINC00662, a long noncoding RNA gene, as a key differentiator. It is highly active in human organoids but remains silent in chimpanzees due to a 7,000-letter viral insertion. This insertion, present in chimpanzees and bonobos, effectively silences the gene, highlighting how viral remnants influence complex biological trait expression. ## Developmental Role of LINC00662 In human cells, LINC00662 shows peak activity during early fetal brain development. When researchers silenced this gene in human organoids, 30-day-old tissue exhibited weaker staining for young neuron markers. This suggests the gene is essential for neuronal maturation and the successful outgrowth of axons, which are critical for brain structural complexity. ## Compensatory Genetic Responses Silencing LINC00662 in human organoids triggered increased activity in genes responsible for axon and dendrite growth. Scientists interpret this as a potential compensatory response by the cellular machinery. These findings demonstrate that retroviral insertions do not just silence genes but can fundamentally rewire the regulatory networks governing brain tissue development. ## Comparative Genomic Insights The research highlights that 8% of the human and chimpanzee genomes consist of retroviruses. While protein-coding genes remain highly conserved, the regulatory differences caused by these transposable elements provide a clearer picture of evolutionary divergence. Understanding these non-coding regions is essential for mapping the unique trajectory of human cognitive development. ## Scientific Implications and Conclusion Published in Science Advances on October 23, the study provides a concrete mechanism for human-chimpanzee brain divergence. By linking specific viral insertions to gene silencing and neuronal maturation, the team offers a new perspective on how ancient pathogens shaped modern human biology, emphasizing the importance of studying non-coding genomic regulatory elements. ## Sources covering this story - https://www.sci.news/othersciences/neuroscience/ancient-retroviral-invasion-human-brain-15160.html — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._