This scientist discovered that an ancient virus infected chimpanzee ancestors 4 MILLION years ago but spared humans, leaving behind DNA that switched OFF a gene involved in chimpanzee brain development! Here's the really crazy part. When researchers removed that ancient viral DNA from chimpanzee cells, the silenced gene switched BACK ON! Neurogeneticist Patricia Gerdes and her team identified 158 ancient viral insertions scattered across the chimpanzee genome, but humans lack these particular insertions. The virus, called PTERV1, inserted its DNA into chimpanzee ancestors millions of years ago. One of those insertions appears to have silenced a gene called LINC00662, which is active during early human brain development. Scientists used CRISPR to remove that viral DNA from chimpanzee stem cells in the laboratory, restoring the gene's activity. But here's another fascinating discovery. The same gene is especially active in developing human brains around 10 to 12 weeks after conception. When scientists suppressed this gene in miniature human brain models grown in the lab, they found reduced development of the extensions that help neurons form connections. Humans have the same gene, but we don't carry the viral insertion that switches it off. Could an ancient viral infection that our ancestors escaped have helped shape why human and chimpanzee brains evolved so differently?