It's unexplainable. I'm no, I'm Hassan Feld. Roughly half the human population has ovaries.

Researchers know they generally come in pairs that they're about the size of cum quats,

shaped like almonds, and that they hold eggs that if they're fertilized can eventually turn

into children. But as a reporter, Bird Pinkerton learned, there's a whole lot researchers

don't know about ovaries. And in order to answer those questions, they might need a rollback

the clock on decades of assumptions. Here's Bird. If you took high school biology, you probably

read in your biology textbook somewhere, some version of a specific story we tell about our ovaries.

So the story starts in utero, Rachel Gross. It's my favorite human biology textbook,

she's a friend, but also a reproductive health reporter. And she gave me a refresher course.

She said that in utero, a fetus is developing limbs and an eyes, but also a bunch of eggs

until the baby is born with maybe around one to two million. And as the story goes,

that is all the eggs that this new little person will ever have.

From the beginning, those eggs start dying off. A few of them are disappearing even as the baby

becomes a child, though most of them are just sort of hanging out, not doing a whole lot.

Until the hormone surges and cycles of puberty start that monthly cycle that many of us know,

called opulation and menstruation. And in that cycle, there's kind of a cohort of the sleeping,

tiny eggs that are recruited. These recruits then start growing. And at 1.1A is ahead of the pack

and starts helping inhibit the other eggs, which I'll die. The winning egg then takes a little

trip through the fallopian tubes, maybe gets fertilized, probably not. And if not, it gets ejected

in the delightfully bloody, sometimes crampy, usually pretty annoying phase of menstruation,

known as a period. Each month or so, the ovaries are losing a bunch of eggs this way,

and then other eggs are also just dying on their own. In your 30s and 40s, the process of eggs

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