Scientists have sequenced the oldest plant genome on record, and it comes from watermelon seeds chomped on by Stone Age sheep herders in the Sahara. The 6,000-year-old watermelon seeds resurfaced in the 1990s during an archaeological dig of the cave site known as Uan Muhuggiag, located along a swath of the Sahara that’s now Libya. Due to the cave’s dry, salty air, the seeds, which may have fallen to the ground during a meal, were well preserved, enabling scientists from the Royal Botanic Gardens, Kew, to sequence their DNA. Examination of the genome also showed that the seeds were those of a wild watermelon, one of Africa’s oldest crops, and probably contained a sickeningly bitter pulp. The discovery is important because it offers information about the domestication of the watermelon…