Female Worms Add a Misandrist Twist to Asexuality in New Study

They use males for sperm, not for genes.

worm, nematodes

The world of small, slender roundworms is the embodiment of “this is the future that liberals want” — as prophesied by someone like Jordan Peterson. It’s not that the species Mesorhabditis belari doesn’t need males. According to a new study, they definitely do. It’s just that the female worms actively exploit men. And they do it so their sons can have sex with their daughters.

So why are M. belari such male-hating misandrists? They’ve figured out, over thousands of years, that it’s just the best way for their species to survive. In a study published Thursday in the journal Science, a team of French researchers explains how it all works.

Scientists have known since 1949 that these worms don’t reproduce through straightforward sexual reproduction. Instead, they’ve observed that the worms use an asexual reproductive strategy called pseudogamy: Females use the sperm of males — and only the sperm — to activate their eggs. No genetic material is passed on from the male, and the resulting embryo develops into a female clone of its mother.

So in short, these worms may need males, but they sure don’t seem to want them.

However, the team behind the new study discovered that the situation is more complicated it appears: In 9 percent of worm births, the embryo produced a male when the sperm genetic material was used after fertilization. Importantly, male DNA is only ever transmitted to sons.

M. belari worms: five females and one male.

That means that M. belari only produce males for strictly reproductive purposes. That tiny 9 percent figure, meanwhile, is an extremely important number to the worms because it means that male genes never re-enter the female gene pool. There are not, for example, lots of young male worms who can go out and sow their wild oats.

Instead, the scientists determined, these few males exist to stay home and share their sperm with their sisters.

“From the viewpoint of the genes of M. belari females, production of sons is of interest for a female only if her sons mate with her daughters (to ensure that a maximum of eggs is fertilized) and do not mate unrelated lineages of females (to which they do not transmit any DNA),” they write. “The reproductive system of M. belari represents a distinctive state, where asexual females systematically produce few sexual males, and male genes never reenter the gene pool.”

Nine percent of males, they explain, is a “stable evolutionary strategy” — it’s enough to ensure that a maximum number of females are produced, without putting too much effort into the production of males. It’s a “novel reproduction strategy” when we look at it through a human lens, but to these worms, it’s just the obvious way to live.


We report the reproductive strategy of the nematode Mesorhabditis belari. This species produces only 9% males, whose sperm is necessary to fertilize and activate the eggs. However, most of the fertilized eggs develop without using the sperm DNA and produce female individuals. Only in 9% of eggs is the male DNA utilized, producing sons. We found that mixing of parental genomes only gives rise to males because the Y-bearing sperm of males are much more competent than the X-bearing sperm for penetrating the eggs. In this previously unrecognized strategy, asexual females produce few sexual males whose genes never reenter the female pool. Here, production of males is of interest only if sons are more likely to mate with their sisters. Using game theory, we show that in this context, the production of 9% males by M. belari females is an evolutionary stable strategy.