Viral Scoop I
“There is good circumstantial evidence that the specific origin of placental mammals is the result of an ancestral species being infected with an immunosuppressive proto-retrovirus. It is suggested that this immunosuppression permitted an immunological accommodation in the mother to the development of a genetically distinct individual in the placenta during a prolonged gestation!”
– pg 9, Basic Virology, Edward K. Wagner, Martinez J. Hewlett, David C. Bloom, and David Camerini