Embryo Development Linked to a 500-Million-Year-Old Viral Infection

A critical early stage of embryonic development has been linked to a virus that mixed with the ancestral DNA of complex organisms like ourselves more than 500 million years ago.

Genetic material from endogenous retroviruses – which infected the earliest organisms on Earth, leaving markers in our DNA – is estimated to make up around 8 to 10 percent of the modern human genome.

https://www.sciencealert.com/embryo-development-linked-to-a-500-million-year-old-viral-infection

Article without much alphabet soup and with illustrations.

They already knew about the syncytial paleovirus that was vital to the development of the mammal placenta--without it, we'd all be marsupials.

Turns out retroviruses can be our friends, as long as they're not killing us off.