Sure, there are moments when we might question if we really need men in a specific situation. Perhaps an exhausted new mom, as she's changing the seventeenth dirty diaper of the day while her man logs eight solid hours of sleep, might wonder what, exactly, sleeping beauty is bringing to the table. But the rest of the time? We love them. Science, however, has a more cutthroat opinion.

According to a study published in the journal Nature, science never really knew why men exist (or rather, why they continue to exist in such large numbers) from a biological perspective. And here's the answer: To participate in sexual selection, which helps the human race become more fit and immune to disease.

Yes, men produce sperm, which is required to create life. But once that life is created, scientists point out that men are not crucial to the human race from a biological perspective. Women produce the milk that babies need, and are perfectly capable of caring for their children solo. Plus, they're the ones who will actually bear the future generation. For that reason, men might appear like a weaker gender that would succumb to natural selection and dwindle in size over time.

Researchers watched flour beetles procreate in order to get an answer. In some cases, they allowed up to 90 males to compete for the sexual affections of just 10 females; in others, just one male was contained with a single female, so that he'd have zero competition before they got it on.

After the beetles bred 50 generations, the researchers made their conclusions: The offspring whose parents were allowed to choose their sexual partners (thanks to a little healthy competition) were in the best health and the least likely to go extinct. By contrast, the beetles whose parents had little or no choice in their partners were exposed to a greater number of genetic mutations that accumulated over time—and because of inbreeding!—whereas the beetles with options were able to steer clear of genetic minefields.

The same principle, the researchers believe, applies to humans. "Mate choice by (usually) females creates important intraspecific filters for reproductive success, so that only a subset of males gains paternity," the study says. We need a large pool of applicants, so to speak, so that we can weed through and pick the healthiest possible mates. So now you know.