Talk about a dry spell. Microscopic bdelloid rotifers have seemingly evolved without sex for millions of years and probably don't exist in male form, say Harvard University biologists.
The bdelloid genome shows an odd pattern of differences between versions of the same genes, report David Mark Welch and Matthew Meselson. This pattern most likely arose during eons without sex, they argue in the May 19 Science.
If further tests prove them right, they will have confirmed the first example of ancient asexuals, organisms much sought after in biology.
Of the planet's 2 million named species, only about 2,000 appear totally asexual, Meselson notes. Hardly any of these lineages seem old, and fossil evidence has suggested that