"We are creatures controlled by viruses," Luis Villarreal, a professor of Molecular Biology and Biochemistry at the University of California at Irvine, tells New Scientist. He's referring to the endogenous retroviruses, or ERVs, that make up about 9 percent of the human genome. Throughout human development, these retroviruses would invade our genome, at first causing death and disease—but as our species evolved a resistance or tolerance, these viruses would become woven into the fabric of our evolution. According to the theories of some scientists, this is how certain species diverge from one another. A virus forces an evolution that gets passed down if it proves beneficial in some way. It was largely thought that the effect of these retroviruses ceased to have an impact on our behavior and evolution thousands of years ago.

But a recent discovery is challenging that assumption. While studying the tiny bundles of just eight cells that comprise 3-day-old human embryos, Joanna Wysocka and her colleagues at Stanford University in California found, in addition to DNA from the parents, evidence of HERVK, the most recent ERV to take root in our DNA, likely some 200,000 years ago.

And HERVK isn't lying dormant in these early embryos: Experiments revealed that the virus appears to produce a protein that prevents dangerous viruses like influenza from penetrating the embryo. It also appears to be aiding in translating genetic instructions to the cellular protein factories. What was once a deadly virus has evolved to be crucial to defense and development of our earliest selves. 

Patrick Forterre of the Pasteur Institute in Paris believes that this corroborates the theory that retroviruses are crucial to species divergence, saying, "It shows that the protein products of a relatively 'recent' retrovirus integration are present very early on in the embryo, and could be involved in some critical developmental programmes."

[h/t New Scientist]