An Asian origin for a 10,000-year-old domesticated plant in the Americas

Abstract

New genetic and archaeological approaches have substantially improved our understanding of the transition to agriculture, a major turning point in human history that began 10,000-5,000 years ago with the independent domestication of plants and animals in eight world regions. In the Americas, however, understanding the initial domestication of New World species has long been complicated by the early presence of an African enigma, the bottle gourd (Lagenaria siceraria). Indigenous to Africa, it reached East Asia by 9,000-8,000 before present (B.P.) and had a broad New World distribution by 8,000 B.P. Here we integrate genetic and archaeological approaches to address a set of long-standing core questions regarding the introduction of the bottle gourd into the Americas. Did it reach the New World directly from Africa or through Asia? Was it transported by humans or ocean currents? Was it wild or domesticated upon arrival? Fruit rind thickness values and accelerator mass spectrometer radiocarbon dating of archaeological specimens indicate that the bottle gourd was present in the Americas as a domesticated plant by 10,000 B.P., placing it among the earliest domesticates in the New World. Ancient DNA sequence analysis of archaeological bottle gourd specimens and comparison with modern Asian and African landraces identify Asia as the source of its introduction. We suggest that the bottle gourd and the dog, two "utility" species, were domesticated long before any food crops or livestock species, and that both were brought to the Americas by Paleoindian populations as they colonized the New World.

Fig. 1.

The archaeological sites that yielded bottle gourd rind samples included in the present study, and direct AMS radiocarbon age determinations (calibrated calendar years) obtained on the samples.

Fig. 2.

A 1,000-year-old bottle gourd seed from Cold Oak Rock Shelter in Kentucky (age in calibrated calendar years: A.D. 760 ± 40, Beta-195535). The seed exhibits morphology typical of Asian landraces (L. siceraria ssp. asiatica) (8, 20): light grayish brown color, length/width ratio >2, “ears” present (ear fragments partially broken off in photo, see Fig. 8), corky “wings” absent, and prominent and finely pubescent lines (seed length, 14.3 mm).