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 hadn’t been infected by a virus hundreds of millions of years ago, humans would reproduce by laying
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It's interesting to think that a virus caused our ancestors give birth without laying eggs. However, getting pregnant and having children would be less stressful if we did...
