Your DNA Contains Viral Leftovers From Ancient Infections

About 8 percent of your DNA comes from viruses. Not from your parents, not from evolution in the traditional sense, but from ancient retroviruses that infected your ancestors millions of years ago. These viral sequences got inserted directly into the germline, the cells that produce sperm and eggs, and then stayed there through countless generations. Some of these viral insertions are now so old that they've been deactivated, their genes no longer functional. But they're still there, embedded in your genome like fossils written in genetic code. Scientists call them human endogenous retroviruses, or HERVs. What makes this stranger is that some of these ancient viral sequences have actually been co-opted by the human body. One such sequence produces a protein in the placenta that appears to be crucial for pregnancy. Your body has essentially repurposed code from an ancient invader to build the organ that keeps a fetus alive. This discovery upended the idea that our DNA is purely our own inheritance. Instead, it's a patchwork archive of our species' encounters with pathogens across millions of years. Every human carries this viral baggage, a reminder that the boundary between self and invader, between what's ours and what was borrowed, is far blurrier than it once seemed.