Even the most useless males in the animal world contribute to the long-term evolutionary fitness of a species, researchers report, by weeding out the genetic flaws that would otherwise doom the females to extinction. 
 
 A study on the subject, published online Monday by the journal Nature, provides an experimentally supported answer to the age-old question, "Why do males exist?" 
 
 The question isn't as frivolous, or as man-hating, as it sounds: For decades, evolutionary biologists have puzzled over the pluses and minuses of sexual reproduction. The arrangement comes at a heavy cost: Only half of the species is capable of producing offspring. 
 
 "We wanted to understand how Darwinian selection can allow this widespread and seemingly wasteful reproductive system to persist, when a system where all individuals produce offspring without sex — as in all-female asexual reproduction — would be a far more effective route to reproduce greater numbers of offspring," Matt Gage, a biologist at the University of East Anglia in Britain, said in a news release about the study. 
 
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 Several explanations have been put forward over the years: For example, when environmental conditions turn stressful, mixing up male and female genes can lead to new combinations of traits that are better-suited to cope with the change. 
 
 Another argument goes all the way back to Charles Darwin, the biologist who pioneered evolutionary theory. He proposed that sexual selection — in which males compete for the favors of females — played a role alongside other forms of natural selection in ensuring the survival of the fittest. 
 
 "The theory is well-developed, but it's very difficult to test it," Ricardo Azevedo, a biologist at the University of Houston who has studied the issue, told NBC News. 
 
 Meet the beetles 
 
 Gage and his colleagues tested Darwin's hypothesis over the course of 10 years, by fiddling with the sex lives of Tribolium flour beetles. The bugs are pests that feed off wheat and other grains, including the food in your pantry. If you've ever come across mealworms in a bag of flour that's gone bad, you know how much of a pain the beetles can be. 
 
 The beetles are also notable for their sex roles: The males contribute nothing to the upbringing of offspring, other than their genes. That makes them well-suited for an experiment aimed at figuring out why the females are better off even if they have to deal with useless males. 
 
 The research team bred several groups of beetles under different conditions — ranging from a scenario where 90 males competed to mate with just 10 females, to a scenario where the females were assigned their mates with no choice in the matter. 
 
 The beetles were bred under these conditions for seven years, representing about 50 generations' worth of bugs. Then each community of bugs was inbred, to reveal whether or not harmful mutations had built up in the beetles' genomes. 
 
 Some of the beetle populations that had been involved in lusty competition were still going strong even after 20 generations of brother-sister pairings. In contrast, all of the populations that experienced little or no sexual selection to begin with went extinct within eight generations of inbreeding. 
 
 Out with the bad genes 
 
 The results suggest that when females aren't allowed to choose fitter mates, the "mutation load" gradually builds up in the genomes of a given population — with disastrous results when the population is put under stress. Gage told NBC News that sexual selection "helps to purge out 'bad genes' from a population." 
 
 Azevedo said the experiment is "very exciting, because it's a very nice demonstration of what other researchers had predicted." 
 
 Gage said it's valid to generalize from beetles to other species, but he stressed that most males are good for more than their genes. 
 
 "The main exception to our model system is in making comparisons with species where males provide important direct benefits to offspring production, such as through care or feeding," he said in an email. "Trends towards monogamy are necessary for ecology to drive those mating patterns to persist (otherwise males will be investing in the offspring that they are not the father of)." 
 
 Thus, it's not quite right to say the study fully explains why men exist. Rather, it shows why even good-for-nothing males exist. One would hope there's a difference. 
 
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 Could super-intelligent females find a way to do without males? Gage noted that such a scenario was outlined in a 1915 novel titled "Herland." The book describes a utopia where women reproduce through parthenogenesis, or "virgin birth." Parthenogenesis occurs in species ranging from sharks to snakes to Komodo dragons, but it has not been documented among mammals in the wild. 
 
 The newly published study shows why it's probably better that way, Gage said. 
 
 "Our findings show that, while populations like 'Herland' get short-term benefits from asexual reproduction and an absence of sexual conflict, they are vulnerable to ... mutation accumulation over evolutionary timescales," he wrote. "Without sexual selection, mutations are less effectively purged from the population, putting it at higher eventual risk of extinction." 
 
 In addition to Gage, the authors of "Sexual Selection Protects Against Extinction" include Alyson Lumley, Łukasz Michalczyk, James Kitson, Lewis Spurgin, Catriona Morrison, Joanne Godwin, Matthew Dickinson, Oliver Martin, Brent Emerson and Tracey Chapman. ||||| A shop worker rests in the shade along the beach in Recife June 10, 2014. 
 
 LONDON Since in many species, sperm is males' only contribution to reproduction, biologists have long puzzled about why evolutionary selection, known for its ruthless efficiency, allows them to exist. 
 
 Now British scientists have an explanation: Males are required for a process known as "sexual selection" which helps species to ward off disease and avoid extinction. 
 
 A system where all offspring are produced without sex -- as in all-female asexual populations -- would be far more efficient at reproducing greater numbers of offspring, the scientists said. 
 
 But in research published in the journal Nature on Monday, they found that sexual selection, in which males compete to be chose by females for reproduction, improves the gene pool and boosts population health, helping explain why males are important. 
 
 An absence of selection -- when there is no sex, or no need to compete for it -- leaves populations weaker genetically, making them more vulnerable to dying out. 
 
 "Competition among males for reproduction provides a really important benefit, because it improves the genetic health of populations," said professor Matt Gage, who led the work at Britain's University of East Anglia. 
 
 "Sexual selection achieves this by acting as a filter to remove harmful genetic mutations, helping populations to flourish and avoid extinction in the long-term." 
 
 Almost all multi-cellular species reproduce using sex, but its existence is not easy to explain biologically, Gage said, because sex has big downsides -- including that only half of the offspring, the daughters, will produce offspring themselves. 
 
 "Why should any species waste all that effort on sons?" he said. 
 
 In their study, Gage's team evolved Tribolium flour beetles over 10 years under controlled laboratory conditions, where the only difference between populations was the intensity of sexual selection during each adult reproductive stage. 
 
 The strength of sexual selection ranged from intense competition -- where 90 males competed for only 10 females -- through to the complete absence of sexual selection, with monogamous pairings in which females had no choice and males no competition. 
 
 After seven years of reproduction, representing about 50 generations, the scientists found that populations where there had been strong sexual selection were fitter and more resilient to extinction in the face of inbreeding. 
 
 But populations with weak or non-existent sexual selection showed more rapid declines in health under inbreeding, and all went extinct by the tenth generation. 
 
 (Reporting by Kate Kelland; editing by Andrew Roche)
– Scientists have long wondered why men exist. Sex between males and females is simply not nearly as efficient as asexual reproduction. But now a group out of the UK is reporting in the journal Nature that, after looking at several years of lab-controlled procreation of the Tribolium flour beetle, they've found that sexual selection—the process by which males compete for females—helps species become fitter and more resilient to disease. "Competition among males for reproduction provides a really important benefit, because it improves the genetic health of populations," the lead researcher at the University of East Anglia says in a press release. "Sexual selection achieves this by acting as a filter to remove harmful genetic mutations, helping populations to flourish." Such a question can be tested on this particular beetle (a pest in many a flour bag) because aside from their genes, the males don't help raise offspring, reports NBC News. In the lab, the scientists controlled the beetle's environments such that the only difference between populations was the strength of sexual selection, which ranged from intense—with 90 males competing for 10 females—to no sexual selection at all, where females were limited to one monogamous partner and thus males didn't have to compete. Seven years (and 50 generations) later, the beetles that resulted from the strongest sexual selection were in the best health and were the least likely to go extinct when inbred, Reuters reports. (Speaking of evolution, a third of Americans don't believe it exists.)