A virus forms the placenta, causes fetal tolerance, and makes muscular males

Nearly 10% of the genome of all mammals is made up of viruses that infected mammalian ancestors eons ago. These retroviruses inserted their DNA into mammalian chromosomes and, while time has reduced many of them to useless genetic rubble, some of them, or fragments from them, became adopted by mammalian DNA and pressed into service […]

from The Evolution and Medicine Review http://ift.tt/2chLtwf