Something to give thanks for.
Imagine a world without pumpkins, squashes or gourds — a world without pumpkin pie, squash soups, pumpkin muffins, or the oh-so-popular pumpkin spice lattes. With no gourds, what would we use to decorate our tables on Thanksgiving? With no pumpkins, what would we be carving at Halloween? Watermelons?
This could have been reality if it were not for early American farmers. Without them, pumpkins, squashes and gourds may have gone extinct in North America. So how did farmers save these delicious fruit from extinction? They domesticated them.
Before humans arrived in the Americas, wild pumpkin, squash and gourds — of the Cucurbita genus — were found all over the landscape. Giant species of herbivores, including the mastadon, ground sloth, and gomphotheres (elephant-like animal with a shovel-shaped jaw), spread seeds through defecation and created open spaces from their grazing, allowing the weedy Cucurbita to grow.
Wild gourds are very bitter. Logan Kistler, molecular anthropologist at the University of Pennsylvania and England’s University of Warwick and his colleagues, tested 46 mammal genomes linked to tasting bitterness, and found smaller mammals had higher levels of the genes — meaning they probably avoided wild pumpkins.
“Cucurbitacins, the compounds responsible for their off-putting taste, are some of the bitterest naturally occurring compounds that we're aware of,” said Kistler. But the size of the herbivores would have protected them from the Cucurbita toxins and their large jaws were capable of crushing the hard rinds. “We have evidence from wild Cucurbita seeds in mastodon dung deposits going back 30,000 years.”
When humans arrived in the Americas between 13,500 and 14,500 years ago, a massive extinction of these herbivores occurred due to overhunting and shifts in climate. Not only did the reduction of the herbivores result in less spreading of seeds, it also changed the landscape by
allowing forests to take over the open plains where Cucurbita thrived.
“There was probably a long-term retreat of wild populations into ecological refugia, habitat zones that were able to support the wild plants even in changing conditions,” says Kistler, but eventually, some of the wild types disappeared altogether. He adds that, “one of the common types of canned pumpkin that a lot of people in the U.S. will be opening up for pies this season has no known wild counterpart [today].”
The researchers used existing and archaeological genome data, and discovered that the domestication of the gourds occurred around 10,000 years ago, almost exactly the same time that the last mastodons walked the earth. Humans may have inadvertently ensured the survival of pumpkins and squash.
So remember this Thanksgiving, as you eat some pumpkin pie, to give thanks to our ancestors for saving our beloved pumpkins, squash and gourds.