Since one in five fungi have no visible Sex lives, covert sex could be commonplace. No wonder some fear for the asexual credentials ot organisms like the bdelloids. It takes two to tango, however, and in the 400 years since bdelloids were first described by naturalists nobody has ever reported seeing a male. Nonetheless, negative evidence seldom wins hearts and minds in scientific debates. And the painful truth is that the discovery of just one male bdelloid, fossilised or alive, would instantly tarnish the bdelloid's reputation and dent biologists' hopes of using these ancient virgins to crack the mystery of sex.
Chivalrous help is at hand.
Meselson and his team have come up with DNA test to establish that no living species or their evolutionary ancestors have swapped genetic material through sex. It's a test for virginity on an evolutionary timescale, and it works by examining the sentences of closely related genes in individuals. In sexual species, chromosomes and the genes they carry tend to come in two versions, one inherited from each parent. The DNA sequences of the two versions are normally almost identical. And it's sex that keeps them that way.