Humans’ role in transforming toxic squash into something tasty

Unless you’re a six-year-old, you probably wouldn’t assume that something sweet like winter squash was ever so bitter and toxic it nearly wiped itself out. While we enjoy (and force the kids to try) many fruits from the Cucurbita family, like pumpkins and squash, their ancestors were basically inedible to all but the largest animals who were able to safely consume them. When megafauna like mammoths and rhinos started going extinct, squashes needed to change their ecology drastically to avoid extinction themselves.

A meal for megafauna

While many plants have evolved defenses against being eaten, those defenses are usually to protect the plant, not its fruit. Fruit and hard seeds evolved to be eaten, digested and then pooped out, dispersing the seeds to new locations. Just as with animal predators and prey, fruits evolved to target specific sets of partners in their ecosystems, growing to appeal to certain species more than others. For squashes, this meant growing small, tough and incredibly bitter fruit due it toxins called cucurbitacins. These toxins could be sickening or even fatal to small animals, but something the size of a mammoth wouldn’t have a problem with it.

When climate change and human activity helped remove most of the world’s megafauna, squash found itself in trouble. The remaining seed dispersing species were much smaller, like mice and birds. The small bodies on these creatures made them more vulnerable to even small doses of toxins, and their genes indicate that they evolved a sensitivity to bitter tastes to avoid those potentially fatal foods.

Picking the sweetest pumpkins

This left the Cucurbita plants in the hands of the same species that helped disrupt its ecology: humans. Humans weren’t big enough to safely chow down on ancient squashes, and even today fall afoul of Toxic Squash Syndrome. But they must have at least been trying these mysterious gourds enough to discover which specimens were on the tastier end of the spectrum and disperse their seeds, probably unintentionally at first.

As this sampling built momentum, the plants became larger, softer and tastier. While some wild varieties still exist, their numbers are tiny compared to the domesticated plants humans now cultivate. So at this point, 10,000 years later, there’s no reason for my first-grader to avoid eating the squash lasagna we had for dinner last night. She just needs to try a bite first.

Source: Why Pumpkins And Squashes Aren’t Extinct by Ed Yong, Not Exactly Rocket Science