There are many fruits and vegetables that might be considered representatives of fall, ranging from ripe apples to whatever turns up in a Thanksgiving casserole. However, few could deny the grip that pumpkins hold on the season. Whether they’re sitting on doorsteps whole, carved into jack-o’lanterns, or being served as pie, pumpkins are an enduring symbol of autumn.

Pumpkins belong to the genus Cucurbita. Members of this genus are commonly known as squash or gourds, but the more scientific term is “cucurbit.” Many cucurbits are beloved grocery store favorites, such as butternut squash, zucchini, and ornamental gourds. The more familiar cucurbits have one thing in common: Domestication. They were selectively bred by prehistoric (or sometimes, more recent) humans in order to enhance their desirable properties. This domestication happened at a very interesting time in natural history, one of extinction, and change.

Pumpkins, acorn squash, zucchini, ornamental gourds, and scallop squash are all cultivars of the species Cucurbita pepo. Images by Trevor Mattea, nociveglia, and Jamain.

Cucurbits are native to the Americas. When migrating humans first arrived, they would have found a wide range of cucurbit species, all inedible, with thick rinds, and bitter toxic flesh. At that time, the only creatures that ate wild squash were now-extinct mammalian megafauna, such as mastodons and giant ground sloths. Their large size allowed them to endure the impact of the cucurbitacin toxins, and they distributed the seeds far and wide in their droppings. Wild squash grew readily on the edges of meadows and other disturbed habitats caused by the foraging habits of these massive beasts. This system worked to the mutual benefit of both megafauna and cucurbits – until that balance was disrupted.

When humans migrated to the Americas, they hunted giant sloths and other large mammals for meat. This new hunting pressure, combined with ongoing climate change, drove the ice age megafauna into extinction. As the megafauna died out, the plants that relied on them for seed dispersal likewise suffered. Unfortunately, most species of wild cucurbit could not adapt fast enough to the changing ecology, and fell extinct. Today, few species of wild cucurbit remain.

While those many cucurbits were going extinct, some persisted due to acquiring another method of propagation: humans. Humans had discovered that the hard rinds of wild squash made for excellent storage containers, though they discarded the inedible flesh inside. Over time, those ancient farmers selected for squash with thinner rinds, smaller seeds, and less bitter toxins. Eventually, this would create a veritable cornucopia of domesticated cucurbit species that were not only edible, but delicious!

DNA evidence suggests that six wild species of Cucurbita were domesticated throughout South America and Mesoamerica through multiple domestication events spanning thousands of years. Evidence points towards the first domestication of a cucurbit occurring around 10,000 years ago, in what is now Mexico. Some of these domesticated species continued to be farmed in the region where their wild ancestors had once grown, while others were spread via human migration.

As humans brought domesticated squash up the east coast of North America, another group of species followed them: Peponapis bees. These stingless bees are specialized to pollinate squash, and now can be found most places where domesticated squash are grown in the Americas.

A squash bee (Peponapis pruinosa) pollinating a squash flower — A squash bee (*Peponapis pruinosa*) pollinating a squash flower

It is undeniable that humans have had a huge impact upon the biosphere of the planet, both in prehistoric and modern times. Some species we destroy, others we save, and yet others we change forever. There are undoubtedly many more examples of the sort of mutual impact that occurred between squash, megafauna, and humanity, but the others will have to wait for another day on the Bruce Science blog!

- Kate Dzikiewicz, Science Curatorial Associate and Seaside Center Manager