The three main problems with sexual reproduction, as explained by science

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Over at PLoS Biology, biologist Denis Roze has a fascinating article introducing a question that may at first seem obvious, but is in fact one of the enduring mysteries of biology: Why bother to have sex? People interested in evolutionary biology may already be familiar with the reasons why sexual intercourse is an improbable evolutionary development, but Roze does a great job summing them up like so:

Many important costs are associated with sexual reproduction, in particular:

The cost of males (or "2-fold cost of sex"): in many species, males do not provide any resource to the next generation, yet sexual females typically invest half of their resources into the production of males. Everything else being equal, this generates a 2-fold advantage for asexual females (producing only female offspring).

The cost of breaking favourable genetic combinations: genotypes that are able to survive to adulthood and reproduce prove that they are relatively fit in their own environment. Reproducing sexually may disrupt beneficial genetic combinations and lower the mean fitness of offspring.

Costs associated with the mating process: finding a mate can be costly in time and energy and may also increase risks of predation and parasite transmission. Furthermore, in some species mating may harm the female and affect her future reproductive success.

Ultimately, however, Roze explains why recent evidence from the real world bolsters the idea that sexual reproduction helps organisms adapt to new environments. He writes:

In particular, several classical biological models proved very useful to explore the benefits of sex during adaptation, with different experimental evolution studies on Chlamydomonas reinhardtii, Saccharomyces cerevisiae, and Escherichia coli, demonstrating that sexual (or recombining) lines adapt faster to new environments than asexual lines. Can this translate into a net benefit for sexuals when competing against asexuals? Evidence for this has been recently provided by experimental populations of the nematode Caenorhabitis elegans, showing that this mostly self-fertilizing organism evolves towards higher rates of biparental sex when adapting to a new environment (or coevolving with a pathogen).


A new study in PLoS Biology shows how sexual reproduction is useful in this way, too. Read more of Roze's article on PLoS Biology.