There is nothing like this interface between the placenta and womb anywhere else in our bodies. When geneticists looked at the gene responsible for creating it, they realized that it was almost identical to those used by retroviruses to produce the proteins that attach to cells they are infecting without triggering an immune response.[24] The scientists concluded that a crucial function of the placenta didn’t emerge gradually as a result of evolution by natural selection but was suddenly acquired when a retrovirus inserted its DNA into our ancestor’s genome. If one of our distant ancestors
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