Why do men exist? It's a question that has been puzzling
women biologists since time began, but now scientists finally have an answer
For decades, biologists have puzzled over how evolutionary selection allows for the existence of males.
After all, a male's only contribution to reproduction is sperm. On the surface, it makes more sense to have an all-female population that is able to reproduce without men.
“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," said lead researcher Professor Matt Gage, from UEA’s School of Biological Sciences.
"Why should any species waste all that effort on sons? All-female asexual populations would be a far more effective route to reproduce greater numbers of offspring."
To test the importance of sexual selection and establish a reason for the existence of males, the researchers allowed a colony of Tribolium flour beetles to evolve over 10 years under controlled conditions.
In some groups, female beetles outnumbered males while in others, 90 male beetles had to compete to reproduce with just 10 females.
After seven years of reproduction under these conditions, the researchers found males who had competed for a female mate displayed higher levels of fitness and were more resistant to inbreeding and disease than those in other groups.
Populations that had experienced weak or non-existent competition showed more rapid declines in health than others.
Beetles who had experienced no sexual selection became extinct after 10 generations.
“These results show that sexual selection is important for population health and persistence, because it helps to purge negative and maintain positive genetic variation in a population," Gage commented.
“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."
The research was funded by the Natural Environment Research Council, the Leverhulme Trust and the University of East Anglia and is published in the journal Nature.
While competing for a mate may improve long-term population health, a previous study suggested men have a shorter life expectancy than women because competing for a female takes its toll on their health, by forcing them to exhibit "risky behaviours" in order to gain attention.
"This whole pattern is a result of sexual selection and the roles that males and females play in reproduction," Daniel J. Kruger, a research scientist in the University of Michigan previously said.
"Females generally invest more in offspring than males and are more limited in offspring quantity, thus males typically compete with each other to attract and retain female partners."