The novel Slotter House 5 includes a strange conversation about sex.

During it, an alien tells a human that, on its planet, they have five separate and unique biological sexes.

This baroque system blows the human's mind.

He grew up thinking about only two sexes, male and female, the thought of five sexes staggers him.

Well, what if I told you that biologists have recently discovered a species similar to the alien system,

and not on some distant planet, but right here on Earth?

It's not humans, although we'll get to that.

It's a type of bird with four separate sexes.

Fittingly enough, this discovery was made by a husband and wife team, two biologists who had their own sad love story.

But during their last years together, they managed to unravel these birds' secret sex life.

And along the way demonstrate why birds and human beings even have different sexes in the first place.

From the Science History Institute, this is Sam Keane and the Disappearing Spoon, a topsy, turvy, sciencey history podcast,

where footnotes become the real story.

The bird in question here is the white-throated sparrow. Here's its chirp.

Some birders describe this melody as, oh sweet Canada, Canada, Canada.

Others here, oh sweet Kimberly, Kimberly, Kimberly.

Regardless, if you've ever been to Canada or the United States, you've almost certainly seen one in a backyard somewhere.

It's quite common, but it probably did not make much of an impression.

That's because the white-throated sparrow is pretty blah.

It's short and plump, and what has a nice touch of yellow around the eyes, it's mostly brown and gray.

Pretty drab.

Still, there is one feature of this bird that you should pay attention to the next time you see one.

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