Scientists have long been puzzling over the all important question: why do men exist? But now they think they've found the answer.
The confusion was why sexual selection - whereby men compete and women choose their partner for reproduction - actually occurs. In some species, the only male contribution to reproduction is their spermatozoa (sperm cell).
But researchers from the University of East Anglia, publishing their findings in Nature, believe selection helps to maintain health in the population and protects against extinction.
Almost all multicellular species on earth reproduce using sex, but its existence isn't easy to explain because sex carries big burdens, the most obvious of which is that only half of your offspring - daughters - will actually produce offspring. Why should any species waste all that effort on sons?
Professor Matt Gage, UEA
To understand the exactly how important sexual selection is, the team studied Tribolium flour beetles over a 6-7 year period in a range of different competition levels.
From one tank where there was extremely high competition - 90 males to 10 females - all the way through to no competition - one male for one female.
At the end of the 6-7 years the team reported that those populations with higher competition enjoyed better overall health and were more resistant to inbreeding.
To be good at out-competing rivals and attracting partners in the struggle to reproduce, an individual has to be good at most things, so sexual selection provides an important and effective filter to maintain and improve population genetic health.
In the absence of sex, populations accumulate deleterious mutations through a ratcheting effect where each new mutation takes a population closer to extinction. Sexual selection helps to remove those mutations, enabling populations to persist against the threat of extinction.