Ann Jones

Does it work in a similar way, though, stopping an unwanted batch of sperm from entering the system?

Having specially developed anatomy to help you choose what sperm goes where is only the very top level of female cryptic choice.

And strap yourself in or on because the ongoing sexual war goes deeper and gets weirder because it involves the protective mechanism that we have too, the immune system.

This is, by the way, Professor Sarah Robertson again from the University of Adelaide.

She's done a whole heap of research into female mice.

And yes, the female immune system has a response to the invasive sperm.

The female doesn't just accept willy-nilly any willy-vanilly that comes her way.

And this all happens in a matter of minutes, within maybe half an hour or so.

So the lining of the uterus has essentially called in the troops, while you, the female mouse, are still searching for your little mousy underwear to put back on.

I like to think of the immune cells a bit like bouncers in this instance.

Not with those shoes, mate.

Get out of here.

Across all mammalian species, responses like this exist.

Professor Susan Suarez is a retired professor of biology at Cornell University.

She has a fish named after her, which is absolutely apt because she has spent most of her career studying little swimmers.

Here she is talking about bull sperm coming into contact with the reproductive tract of a female cow.

And yes, you, human, mammal, in the big family of mammals along with cows and mice, your body, or the body of your mother, has similar responses, sorting out good semen, modifying their immune response to facilitate implantation, or not.

Ah, that is the snowplough of sexism in science coming through again.

And while we're being outraged, have you considered what the penis is actually delivering to the female body?

Of course, it's the wriggling sperm.