Sex is a messy, inefficient method of reproducing, but most multicellular organisms have evolved to rely on a partner regardless. It’s generally accepted that species accept the inefficiency of sexual reproduction because something about the process gives us an evolutionary boost. A new study used 50 generations of beetles to examine just how important sexual selection – the act of choosing one potential partner over another – is to the survival of a species.

From a purely biological standpoint, the existence of the male sex is kind of perplexing: When it’s time to create a new generation, the males of a species often contribute nothing but genetic material to the mix.

“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,” lead author Matt Gage said in a statement. “Why should any species waste all that effort on sons? 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 populations – would be a far more effective route to reproduce greater numbers of offspring.”

Sure, many males are deeply involved in the rearing of their children – take penguins, sea horses and humans, for example – but in extreme cases, males are nothing but parasitic sperm-producers that latch onto their females of choice. It’s odd that 50 percent of most species are capable of producing young, and 50 percent are just around to provide genetic variety. One explanation is that sex allows for sexual selection, which is inherently good for the species. When females get to choose one male over another (or vice versa, depending on the sexual politics of the species), there’s a better genetic outcome for the species than when sex just happens at random.

To test that, researchers at the University of East Anglia created an experiment that removed selection from sex.

The research, published Monday in Nature, took 10 years – and an awful lot of beetles. Fifty generations of them, to be exact.

To test how important selection is to the benefits of sexual reproduction, they pulled selection out of the equation. In one test group, beetles were randomly paired up into monogamous couples. Others had an increasingly uneven male-to-female ratio, with the most extreme group having only 10 females to 90 males. That meant the ladies had plenty of choices, whereas the control group females had no choice at all.

After seven years under those conditions, the researchers tested how resilient each group was to inbreeding, with a brother and sister being mated every generation. The groups that had been allowed the most selection survived as many as 20 inbred generations, while all the groups with weak or non-existent selection went extinct by the 10th. That’s because they had a greater number of dangerous mutations built up in their genetic code, and those quickly accumulated when inbreeding occurred.

Sexual selection gave the beetles an edge, because females with a choice – and many males competing for their attention – were less likely to mate with genetic losers.

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