The above image shows a human embryo at 45 days. Scientists reported that a strange protein called Hemo, courses through the veins of pregnant women. It is made in her fetus and in the placenta.
These viral genes co-opt the cell’s machinery, using it to make new viruses that escape to infect more cells. Over the generations, the viral DNA mutates, and endogenous retroviruses eventually lose the ability to infect new cells.
Hemo is not the only protein with such an alien origin. Our DNA contains roughly 100,000 pieces of viral DNA. Altogether, they make up about 8 percent of the human genome. Some of our ancient viruses may be protecting us from disease, while may be raising our risks for cancer, among other conditions.