Fossilized peach pits discovered in 2-million-year-old rocks in southwestern China reveal that the sweet, fleshy fruit we enjoy today evolved under natural selection – long before we cultivated them. According to findings published in Scientific Reports this week, peaches predate the Pleistocene arrivals of both Homo erectus and Homo sapiens.
Back in August of 2010, road construction near the North Terminal Bus Station of Kunming, Yunnan Province, exposed late Pliocene rock outcroppings of the Ciying Formation. These contained tropical and subtropical plant fossils including ring-cupped oak and peach pits (called endocarps). These elliptical pits were flattened, and up to 3 centimeters (1.2 inches) long and 2 centimeters (0.8 inches) wide.
A team led by Tao Su from the Chinese Academy of Sciences examined the eight fossilized peach endocarps and confirmed that they are 2.6 million years old. The seeds inside the stony pits had been replaced by iron, and the walls of the pits were recrystallized. Until now, the oldest evidence for peaches came from Chinese archaeological records dating back 8,000 years, but no wild population had been confirmed, and the long trade history of peaches and its complex genomics made it difficult to trace their origins.
The team also revealed that the prehistoric pits are identical to those found in modern varieties of peaches, Prunus persica. These identical morphological characters include a single deep groove that extends from the apex to the base on one side, a ridge on the other side, and the presence of deep pits and furrows on the surface. They haven’t found any other parts of the ancient plant yet, but the team proposes a new species name for the fossils: Prunus kunmingensis.
Based on the correlation between modern peach and pit sizes, the team estimate that the late Pliocene peach was 5.2 centimeters (2 inches) in diameter. That’s about the size of the smallest peach you’d find in markets these days. Both size and variation increased as a result of domestication, agriculture, and artificial breeding much later on. But before that, fruit-eating mammals including prehistoric primates likely helped disperse the wild peaches – playing a key role in the fruit’s evolution. "The peach was a witness to the human colonization of China," study co-author Peter Wilf of Penn State said in a statement. "It was there before humans, and through history we adapted to it and it to us."
Image in the text: Homo erectus may have had peaches similar to those we consume today. Rebecca Wilf