Whether it's sliced on top of a a salad, tucked in a California sushi roll, or mashed as guacamole in a burrito, people seem to love avocados. In fact people in the United States munched through 4 Billion of them in 2014 alone. They taste great, they're good for you, but one of the most amazing things about avocados is that they still exist.

See they had a special relationship with huge beasts that lumbered around central America tens of thousands of years ago, and when these animals went extinct avocados could easily have gone down with them, but luckily for us they were saved by some prehistoric farmers. The word avocado comes from the Aztecs specifically the Nahuatl word ahuacatl, which means testicle.

I mean you can kind of see where they got the name, it probably has something to do with the shape and texture of avocados, the way they hang from trees. Anyway before they became popular in the rest of the world, they were cultivated in Mesoamerica for thousands of years.

Avocados are a fruit, basically swollen plant ovaries, so nutritionally they're very different from other fruits you'd find at the supermarket. Fruits like apples and oranges are composed mostly of water and sugar. And in general fruit is probably better for you than a bag of sweets or a sugary drink, because it contains fiber which slows down sugar absorption and makes you feel fuller faster.

By comparison avocados have much less sugar but more protein and fat. That gives them that smooth creamy texture, but it also puts them on the calorific side for a fruit anyway. They also contain high levels of potassium and folate nutrients as well as vitamin C, E, and K, and technically avocados are berries like grapes and blueberries.

Rather than holding lots of little seeds the avocado goes all in on one big seed. That massive ball at the core of each fruit.  And avocados with their huge seeds evolved alongside equally huge guts.

Tens of thousands of years ago during the Pleistocene Epoch, a menagerie of megafauna or giant animals roamed the Americas. While woolly mammoths chilled out in the north, ground sloths weighing 3 tons, and armadillos the size of cars lived in the warm equatorial forests. These giant sloths and armadillos ate a lot of avocados. Their digestive systems would break down the tough skin and absorb the high-energy pulp.

Then the indigestible seed which contains bitter toxins that kept the animals from chewing it up passed right out the other end. The animals got a tasty meal, and the avocado trees got to scatter their offspring throughout the Mesoamerican forests. Plus the seeds got some nice warm fertilizer, to give them a nutritious boost. And with these megafauna around to eat the fruit, the avocados could keep growing berries with increasingly massive seeds.

The bigger the seed the more nutrients could be stored inside as a starter kit for the baby tree. This is especially useful in dense tropical forest where canopies of older trees block out much of the light for the saplings below, so instead of depending entirely on sunlight for energy the avocado seedlings could supplement their photosynthesis with nutrients in their seed to survive.

This happy evolutionary match didn't last though. Eventually, the megafauna suffered a mass extinction around ten to thirteen thousand years ago. We don't know exactly why, but scientists think the warming climate at the end of the last Ice Age was partly responsible. Though, it was also suspiciously close to the time humans began spreading across the Americas, no doubt enjoying lots of giant-mammal meat along the way. This meant avocados were in trouble. Without their large-gutted evolutionary partners, the trees stopped thriving, their fruit fell to the ground, and the seeds mostly just became food for mold. But more hungry creatures were nearby. 

The new human arrivals loved the avocado's flesh as much as the ground sloths did. They also had the tools to eat them, and the brains to figure out how to grow them. Avocados were all set for domestication. The avocados we eat today probably a little different from the ones that grew tens of thousands years ago. For example, thanks to artificial selection, they probably have more pulp than their ancestors. But they've kept their huge seeds, ready and waiting for the guts of long-dead beasts. 

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