It all started with a Mexican yam.

It was 1942 and a chemistry professor from Pennsylvania was looking for a cheap source of progesterone. The hormone had many uses at the time, including preventing miscarriages and treating women going through the menopause.

In fact, Russell Marker already had invented a way to make progesterone from a chemical in certain plants. One option was the tubers of wild Japanese yams. But these were thin and weedy – they just didn’t contain enough of the hormone.

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Marker scoured the land for alternatives, examining more than 400 species, but to no avail. Then he stumbled upon a drawing in an obscure botany book. This yam had fat, knobbly roots that reportedly weighed up to 100 kg (220lbs). He travelled to its native Mexico and smuggled one out of the country.

With an affordable source of progesterone found, researchers turned to its uses as a contraceptive. The birth control pill hit the market less than a decade later. Marker, on the other hand, mysteriously disappeared from public life and became obsessed with collecting silver.

The economic and social side effects of the pill were as profound as they are well-documented. Sex could be enjoyed without fear of pregnancy. Suddenly women could devote their 20s and 30s to furthering their education and careers, rather than housework and nappies.