Would you be surprised to find out that you are only mostly human?

Alongside being predominantly human, we are also part virus, around 8 percent virus, to be more precise. It seems a safe assumption to think that all of a person’s DNA is human, but that is not entirely true.

DNA is the blueprint for life and the template used to construct every part of a person. It determines everything from what eye color you have to how tall you are to how all of your internal stuff works. Throughout human history, viruses have snuck in and become a significant part of our genetic structure.

Viruses are different from bacteria in many ways but one important distinction is that viruses cannot reproduce on their own. They need a host cell in order to make more copies of themselves. Viruses insert parts or all of their genetic material into their host cell’s DNA in order to hijack their energy and machinery. They essentially manipulate a cell into doing all of the work for them. The cell produces more virus and they go on to commandeer more cells, spreading the infection.

If that viral genetic material is inserted into the right cells, it can be passed down from person to person. Hundreds of thousands of years ago, our ancestors got infected and began handing down those viral genes.

We can now see the remnants of those ancient infections through the remains of the viral genetic material that is left in our genome. Our DNA has become a viral graveyard of sorts. Much of that viral DNA is mutated and harmless now, but some has been repurposed to serve our own goals.

Some of the ancient viral genes are crucial components of proper fetus development during pregnancy. Others act as homing beacons to alert the immune system to sick or dysfunctional cells. We have taken a bit of revenge on those viruses. We turned their abilities that were meant to harm us into something we could use.

Viruses have been our constant companion as humans evolved. Our history and development has been greatly influenced by our relationship with viruses. So, it seems logical to think that they have also taken over just a small bit of us as well.

Emily Leclerc is a graduate student at Boston University pursuing her master’s degree in journalism. She hopes to be a science writer.

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