Why sex is here to stay

E coli bacteria: Go forth and multiply

UK scientists have worked out why creatures which reproduce sexually, such as humans, have not been overrun by those which reproduce asexually.

It is a problem that evolutionary experts have wrestled with for more than 30 years.

Asexual organisms can simply split themselves to produce offspring and can therefore effectively reproduce twice as fast as sexual organisms, which require a male and a female.

The ease and speed at which the clone population can increase should in theory swamp the slow progress of sexual organisms. But both types exist.

Clone competition

A team at the University of Southampton used computer models to study how the two groups might compete with one another for food and other essential resources in a virtual environment.

Sexual reproduction leads to variety

"The asexual organisms are all clones and therefore all chase the same food," Dr Simon Cox, one of the team, told the BBC.

In other words, the identical nature of all the clones means they all specialise in the same kind of existence and are all competing against one another for the same resources.

Dr Cox's colleague, Dr Patrick Doncaster, added: "The asexuals do themselves in. They are ridden with competition so they negate their own threat to the sexual species."

Stable outcome

Sexual reproduction creates genetically diverse offspring which means they can exploit a range of resources and compete less against one another.

"Co-existence is the stable outcome," said Dr Doncaster. "The sexual and the asexual can co-exist quite happily even though the sexual one reproduces at half the rate of the asexual one."

A further advantage of sexual reproduction is that harmful mutations can be erased quickly, rather than faithfully copied to every subsequent generation.

The research is published in the journal Nature.