By land or by sea? That’s the question scientists have been pondering for decades when it comes to the bottle gourd, a plant with a hard-skinned fruit that’s used by cultures all over the world to make lightweight containers and other tools. Archaeologists know that people were using domesticated bottle gourds in the Americas as early as 10,000 years ago. But how did the plant make the jump from its original home in Africa to the New World with an ocean in the way? A new study overturns previous evidence pointing to a human-assisted land migration and concludes that the bottle gourd floated across the Atlantic Ocean to the Americas on its own.
Humans rarely eat the bottle gourd (Lagenaria siceraria), but rather dry out its fruit and fashion it into containers, tools like fishing floats or pipes, or even musical instruments. The plant comes in two subspecies linked to their geography: one from Africa, where the plant first evolved, and one from Asia. Researchers have long wondered whether the New World bottle gourds are more closely related to the African or Asian subspecies. If they could build a bottle gourd family tree, they thought, they might be able to figure out how the plant reached the Americas in the first place. Did it float over on ocean currents from Africa, the prevailing assumption until about 10 years ago, or did humans carry the plant with them when they walked across the Bering land bridge from Asia?
“It was a real puzzle,” says Bruce Smith, an archaeologist at the Smithsonian Institution’s National Museum of Natural History in Washington, D.C.
Then, in 2005, a study was published that seemed to solve the mystery once and for all. In a paper published in the Proceedings of the National Academy of Sciences, researchers analyzed the genetics of bottle gourds for the first time and found that pre-Columbian bottle gourds in the Americas appeared to be more closely related to the Asian subspecies than the African one. They concluded that the ancestors of New World bottle gourds must have been carried by people as they made their way across Asia, over the Bering land bridge, and down into the Americas.
But many scientists—including several of the study’s authors—had “lingering questions” about that hypothesis, says Andrew Clarke, a plant biologist at the University of Warwick in Coventry, U.K. and an author of the 2005 study. Most glaringly, how could the bottle gourd, a tropical plant, make it through years of traveling across the Arctic? And if humans carried it with them across the Bering land bridge, why is there no archaeological evidence of bottle gourds in Siberia, Alaska, or the Pacific Northwest?