Sex gives worms the power to fight off parasites, report researchers this week in the journal Science.
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.
:: Read more here ::