Studies on other captive viruses have revealed that some help ward off viral invasions. One virus protein, syncytin, is essential for our being born at all.
“The only place it’s expressed is in the placenta,” Dr. Heidmann said. To understand its function, he and his colleagues disabled the gene in mice. Without syncytin, mice developed deformed placentas, and their embryos died.
Syncytin started as a surface protein on retroviruses that fused them to cells. When mammals captured the gene, they used it in the placenta to create a layer of fused cells through which mothers can send nutrients to their embryos.
The body is, thus, not a unified and coherent source from which our being-in-the-world may be derived, but, instead, a total badass, killing and incorporating vicious virii like the souls of fallen enemies. Also.
Borna Virus Discovered in Human Genome – NYT