The Queen of Problems in Evolutionary Biology

Sexual reproduction is widespread amongst higher eukaryotes. But why are there not many more organisms reproducing asexually? After all, an asexual organism avoids making males, can thus in theory reproduce more efficiently, and one asexual mutant should quickly lead to the extinction of a sexual source population. Owing to such arguments, understanding the evolution and maintenance of sexual reproduction has in 1982 been called ‘the queen of problems in evolutionary biology’. In the last four decades, we have gained tremendous insights into this issue: perhaps most importantly, we understand more clearly that the powerful arguments against sex are not fully realised in all species. There are also recent insights into understanding the maintenance of sex in species where the problem is (partially) realised. Experimental evolution studies show that outcrossing can speed up the response to selection, while studies on natural populations emphasise the importance of niche differentiation and parasites.