An interesting story about darwinulids. As far as anyone could tell, darwinulids (a type of crustacean) had been reproducing exclusively asexually for 200,000,000 years, but now a researcher has found 3 male specimens, which implies that at least one darwinulid species has sex.
Sex is a bit mysterious in evolutionary terms because it’s so much more efficient to reproduce asexually. Quite apart from the time-consuming business of finding a mate, sexual reproduction needs twice as many adults to produce the same number of offspring, and when you do breed, only half your own genes end up in the child anyway. That’s a huge reproductive disadvantage; yet pretty much all animals have sex. So it must offer some kind of dramatic short-term advantage to compensate for that reduced breeding rate. Even animals like aphids, which mainly breed asexually (aphids are born pregnant!) occasionally produce a few males and breed sexually as well.
The most popular theory is apparently that it helps fight disease and parasites – read The Red Queen by Matt Ridley for the details – but certainly its omnipresence implies that sex serves some kind of vital role. Which makes it hard to explain the few groups of animals that seem to have been merrily getting along without for tens of millions of years. If it is confirmed that darwinulids have been secretly shagging away somewhere all along, it removes an anomaly. That still leaves the marvellously named bdelloid rotifers, who have apparently been holding out for 40,000,000 years.