The oldest known seeds from a watermelon relative, dating back 6,000 years to the Neolithic period, were found during an archaeological dig in Libya. An investigation of these seeds led by biologist Susanne S. Renner at Washington University in St. Louis reveals some surprises about how our ancestors used a predecessor of today’s watermelon.

These results and two new genomes of ancient seeds are published in the journal Molecular Biology and Evolution.

Scientists generally agree that watermelons came from Africa, but exactly where and when watermelons with red, sweet flesh were first domesticated from their wild form is debatable. The most recent data point to watermelon getting its start in the Nile valley, which is consistent with archaeological evidence.

However, the very old seeds discovered at Uan Muhuggiag, a rock shelter in what is now the Sahara Desert in Libya, seemed at odds with this explanation. There was no way to be certain of their identity prior to this investigation.

“The oldest seeds of watermelons cannot be securely identified as either belonging to a sweet-pulped domesticated form, or instead to one of the bitter-pulped wild forms,” said Renner, an honorary professor of biology in Arts & Sciences. “The seeds of the seven species of Citrullus are basically undistinguishable.”

“Now, having a chromosome-level genome, we can be sure that Neolithic Libyans were using a bitter-fleshed watermelon,” she said. “We suspect they used the fruits to get at the (numerous!) seeds, which even today are eaten air-dried or roasted or also boiled in soups or stews.”

Read more: Seedy, not sweet