Fun fact, Syncytin-1 is the syncytin used by primates, other branches of mammals have other forms of syncytins, meaning that the event of being infected by a re

Fun fact, Syncytin-1 is the syncytin used by primates, other branches of mammals have other forms of syncytins, meaning that the event of being infected by a retrovirus that gives mammals proteins necessary for the placenta happened several times in history following the original event and replaced the original syncytin. (Not sure those proteins are also called syncytins in other mammals but I'm not a biologist so I'm using the limited vocabulary I have)