About 8% of your DNA comes from ancient viruses
Roughly a twelfth of your genome was left behind by viruses that infected your ancestors millions of years ago, and you'd never have been born without them.
Somewhere in your DNA sits the wreckage of an ancient epidemic. Around 8% of the human genome is made of human endogenous retroviruses (HERVs), the genetic fossils of viruses that infected our primate ancestors millions of years ago and never left.
Retroviruses, like HIV, work by splicing their genes into a host cell’s DNA. When they happened to infect egg or sperm cells, that viral code could be passed to offspring, generation after generation, until it became a permanent part of the human blueprint. Most of these inserts are now broken and silent. But not all of them.
The most striking example is a gene called syncytin. It was once a virus’s tool for fusing into our cells, and evolution repurposed it for something we couldn’t live without: the placenta. Syncytin drives the fusion of cells into the syncytiotrophoblast, the layer that lets a mother’s blood nourish her fetus without their tissues mixing.
Pregnancy in mammals depends on a protein our ancestors stole from a virus.
In other words, a feature that makes us mammals, the ability to carry live young, was handed to us by an infection. The viruses that once attacked our ancestors became, quite literally, a part of what we are.
Sources & references
2 referencesWell-established. Corroborated by 2 independent sources.
