Worms forced to reproduce asexually succumbed to a nasty bacterial infection and died. The researchers say the results are the most convincing evidence to date for a key theory in evolutionary biology. The theory holds that sex evolved because it lets organisms reshuffle their genes into new combinations to stay a step ahead of parasites.
Mating with Neanderthals and another ancient group called Denisovans introduced genes that help us cope with viruses to this day. Previous research had indicated that prehistoric interbreeding led to up to 4% of the modern human genome. The new work identifies stretches of DNA derived from our distant relatives.