Fossilized peach pits (Image by SU Tao)
The oldest peach pits have been found near a bus station in China, according to a new study that sheds new light on the little-known evolutionary history of the fruit.
The eight fossilized peach endocarps, or pits, date back more than two and a half million years. They were found by Tao Su, associate professor at Xishuangbanna Tropical Botanical Garden, when road construction near his house in Kunming, capital of Yunnan in southwest China, exposed a rock outcrop from the late Pliocene.
Preserved within the Pliocene layers, the fossils looked “strikingly modern,” according to Su. With colleague Peter Wilf, a professor of paleobotany at Pennsylvania State University, and others, Su detailed his findings last week in Scientific Reports.
“The fossils are identical to modern peach endocarps, including size comparable to smaller modern varieties, a single seed, a deep dorsal groove, and presence of deep pits and furrows,” the researchers wrote.
The discovery suggests that peaches, juicy and sweet, much like the ones we eat today, were a popular snack long before the humans arrived on the scene.
After analyzing the morphological characters of the pits, the researchers concluded they belonged to the genus Prunus and proposed a new species name, Prunus kunmingensis.
“We aim to provide an unambiguous epithet for the fossils in the absence of a whole-plant reconstruction,” the researchers said.
A popular tree fruit worldwide, with an annual production near 20 million tons, peach (Prunus persica) is widely believed to have originated in China. However, much of the evolutionary history of the fruit remains unknown.
The oldest evidence had been found within archaeological records dating back roughly 8,000 years, but no wild population has ever been found.
The discovery of Prunus kunmingensis supports the belief that the peach originated in China.
“The peach was a witness to the human colonization of China. It was there before humans, and through history we adapted to it and it to us,” Wilf said.
Several tests carried out at Penn State University confirmed that the pits, preserved in the Pliocene rocks along with many other plant fossils, are more than 2.5 million years old.
Electron microscope analysis showed that the seeds inside the flattened pits were mostly replaced by iron oxides, while radiocarbon dating of the fossils showed them to be older than the range of radiocarbon dating, which is about 50,000 years.
The researchers explained that peaches evolved their modern morphology under natural selection, with animals and primates snacking on the fleshy fruit and dispersing their seeds.
Much later, peach size and variety increased through domestication and breeding.
So what did Prunus kunmingensis look like? Su and colleagues compared the size correlation between pits and fruits in modern peaches, and concluded that the size of the fruit in the late Pliocene was about 5.2 cm (2.05 inches) in diameter.
“If you imagine the smallest commercial peach today, that’s what these would look like,” Wilf said.
“It’s something that would have had a fleshy, edible fruit around it,” he said. “It must have been delicious.”