Preceramic Adoption of Peanut, Squash, and Cotton in Northern Peru. Tom D. Dillehay, Jack Rossen, Thomas C. Andres, David E. Williams. Science 29 June 2007: Vol. 316. no. 5833, pp. 1890 - 1893
The early development of agriculture in the New World has been assumed to involve early farming in settlements in the Andes, but the record has been sparse. Peanut (Arachis sp.), squash (Cucurbita moschata), and cotton (Gossypium barbadense) macrofossils were excavated from archaeological sites on the western slopes of the northern Peruvian Andes. Direct radiocarbon dating indicated that these plants grew between 9240 and 5500 14C years before the present. These and other plants were recovered from multiple locations in a tropical dry forest valley, including household clusters, permanent architectural structures, garden plots, irrigation canals, hoes, and storage structures. These data provide evidence for early use of peanut and squash in the human diet and of cotton for industrial purposes and indicate that horticultural economies in parts of the Andes took root by about 10,000 years ago.
Earlier, I wondered whether the identification of domesticates was based on their location outside of the known natural ranges. This turned out not to be the case for all. The peanut specimens (7840 BP) are said to closely resemble a wild species which they argue reflects its early stage of cultivation, and this one is thought to represent an agricultural item that is outside its normal range. Squash, however, was ID'd as domestic based on the seed characteristics: Seeds of this size, shape, and color have been found in fruits of modern traditional landraces of C. moschata from lowland northern Colombia (14). No other species of Cucurbita resemble these traits.
The other species seem to have been identified based on morphological similarities to modern domesticated species. One thing I don't follow is why peanuts should still look like their wild progenitors while the others, notably squash, have already changed morphologically. Unless I missed something on the dating.
The text indicates that these dates are in line with (variable) dates from other sites and indicates that, since none of the plants are native to the area, were cultivated earlier elsewhere; i.e., this isn't a primary site of domestication. The key, it seems to me, is that this supplies more data indicating that domestication and early cultivation occurred in the New World nearly as early as that in the Old World:
Our data also show that horticulture and cultural complexity developed in the Americas nearly as early as it did in many parts of the Old World. Early to middle Holocene populations exploiting suitable environments in both the Old World and New World combined different suites of resources and technologies to affiliate into larger, more advanced communities that differentiated themselves from others between 12,000 and 9000 yr B.P.