A recent study that looked at the population benefits of sexual selection explained why men still exist.
In many species, males only contribution to reproduction is spermatozoa, the University of East Anglia reported. This has caused scientists to wonder why evolutionary selection facilitates the existence of males at all. The new study shows that when males compete and females have the opportunity to choose who they reproduce with, it improves overall population health.
"Sexual selection operates when males compete for reproduction and females choose, and the existence of two different sexes encourages these processes. It ultimately dictates who gets to reproduce their genes into the next generation - so it's a widespread and very powerful evolutionary force," said lead researcher Matt Gage, from UEA's School of Biological Sciences. "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?"
All-female asexual populations seem as if they would be more efficient, but this new research demonstrates how sexual selection acts as a "filter" to eliminate negative genetic mutations. In order to do this, a team of researchers evolved Tribolium flour beetles over the course of a decade. They ranged the strength of sexual selection from 90 males competing for 10 females to no sexual selection at all (beetles forced into monogamous pairs with no opportunity to choose).
After about seven years, which encompassed about 50 generations, the researchers observed the group with strong sexual selection had higher levels of fitness and were less susceptible to the consequences of inbreeding. Some of these populations survived as many as 20 inbreeding generations in which a brother and sister mated. The populations that had little to no sexual selection showed rapid declines in 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," Gage said.
The findings were published in a recent edition of the journal Nature.
