Sex and evolution

An increasing number of studies appear to support John Maynard Smith's hypothesis that sex is a way of reducing the load of deleterious mutations a species carries. Eureka Science News reports another one, based on the water flea Daphnia pulex. The paper in Science is here and the commentary here.

The authors studied both sexual and asexual lineages in these organisms (a species complex rather than a single species) and found that the asexuals tend to accumulate deleterious mutations faster than the sexual lineages. "The ratio of the rate of amino acid to silent substitution ... in mitochondrial protein-coding genes is higher in obligately asexual lineages than in sexual lineages", they write.