Peaches Preceded Humans: Fossil Evidence from SW China

Abstract

Peach (Prunus persica, Rosaceae) is an extremely popular tree fruit worldwide, with an annual production near 20 million tons. Peach is widely thought to have origins in China, but its evolutionary history is largely unknown. The oldest evidence for the peach has been Chinese archaeological records dating to 8000-7000 BP. Here, we report eight fossil peach endocarps from late Pliocene strata of Kunming City, Yunnan, southwestern China. 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. These fossils show that China has been a critical region for peach evolution since long before human presence, much less agriculture. Peaches evolved their modern morphology under natural selection, presumably involving large, frugivorous mammals such as primates. Much later, peach size and variety increased through domestication and breeding.

Figure 1. Fossil locality in Kunming, Yunnan Province, southwestern China.

(a) Geologic map, modified from Bureau of Geology and Mineral Resources of Yunnan Province, 1990 with the software Adobe Illustrator CS4. (b) Stratigraphic section, arrow showing the fossil-bearing layer; inset shows fossil peach endocarp in situ.

Figure 2. Prunus kunmingensis.

(a–e) KUN PC2015001-KUN PC2015005. (f) CT scan showing longitudinal section and seed (KUN PC2015001). Scale bar = 1 cm. See the three dimensional reconstruction in Animation S1.

Figure 3

Morphological comparison of endocarps between Prunus kunmingensis (a,c,e) and modern peach (b,d,f). (a,b) Gross morphology. (c,d) Endocarp interior surface with linear striations. (e,f) Diagenetically altered fossil sclereids (e) and modern sclereids (f) along a transverse section of the endocarp. Scale bars: a–b = 1 cm; c–d = 30 μm; e–f = 15 μm.

Figure 4. Nonmetric Multidimentional Scaling analysis of 36 Prunus species based on 12 morphological characters of endocarps.

Prunus kunmingensis and modern peach share the same character scores. Data listed in Supplementary Table 1.

Figure 5. Size correlation between endocarps and fruits in modern peach cultivars and estimated fruit size in the fossil Prunus kunmingensis.

Data from modern cultivars are measured from photographs in Wang et al. 2012 and listed in Supplementary Table 2. Lines indicate the fossil endocarps of Prunus kunmingensis, whose inferred fruit diameter, based on the correlation shown here (solid black line), is ~5.2 cm.