People, Plants, and Landscapes: Studies in Paleoethnobotany

4. Evolutionary Changes Associated with the Domestication of Cucurbita pepo: Evidence from Eastern Kentucky

CHAPTER 4 Evolutionary Changes Associated with the Domestication of Cucurbita pepo Evidence from Eastern Kentucky C. WESLEY COWAN Thanks to the "flotation revolution:' the broad outline of the evolution of field agriculture in eastern North America is arguably the best such record in the world (Cowan and Watson 1992; Smith 1992). The past two decades, for example, have seen the formal identification of two extinct domesticates (sumpweed [Iva annua var. macrocarpa] [Yarnell 1972] and chenopod [Chenopodium berlandieri ssp.jonesianum] [Smith and Funk 1985]) as well as three other weedy annuals that were intensively cultivated in various portions of the Midcontinent (maygrass [Phalaris caroliniana], erect knotweed [Polygonum erectum], and little barley [Hordeum pusillum] [Asch and Asch 1978; Cowan 1978a; Smith 1992b]). Along with the familiar sunflower (Helianthus annuus), which was also probably domesticated by eastern populations, these plants form a distinctive crop group whose evolution occurred in the North American Midwest and Southeast sometime between about 6000 and 3000 B.P. It is safe to suggest that at least among eastern archaeologists and many plant taxonomists this developmental trajectory is widely accepted. In addition to these relatively obscure-at least by public standards -annuals, there is another plant whose status as an eastern domesticate has been the subject ofintense debate in recent years. "Squash:' or at least a primitive form of Cucurbita pepo,l has also been found in archaeological and paleontological deposits in widely spaced areas in the eastern United States in contexts that predate the intensive use of the weedy annuals.This debate focuses on the issue ofwhether Cucurbita 64 C. Wesley Cowan pepo was introduced into eastern North America from a Mesoamerican homeland or was domesticated in the East independently of Mexico (see Asch and Asch 1992; Cowan and Smith 1993; Decker-Walters et al. 1993; Smith 1992; and Smith et al. 1992 for recent summaries of the various positions). Recent genetic evidence suggests that at least one lineage of Cucurbita pepo (ssp.ovifera) evolved in situ in eastern North America (DeckerWalters et al. 1993). The progenitor of this lineage seems to have been similar to, if not identical to, wild gourds whose modern distribution encompasses a broad area of the southeastern United States (Cowan and Smith 1993; Smith et al. 1992). The occurrence of abundant C. pepo seeds in a paleontological site in Florida directly dated to the thirteenth millennium B.P. adds considerable strength to the argument that a wild gourd has been a member of an indigenous eastern flora since at least the end of the Pleistocene (Newsom et al. 1993). These parallel lines of evidence point to the independent domestication of at least some varieties of summer squashes and ornamental gourds (those placed in Cucurbita pepo ssp. ovifera var. ovifera) within eastern Nortp America. In spite of the fact that a likely progenitor for these important crops has been identified, knowledge of the evolution of Cucurbita pepo spp. ovifera in the East remains incomplete. In part, our understanding of this process is hindered by physical and cultural factors that place limits on the kind and size of archaeological remains available for study. Cucurbita remains are generally not common in any archaeological contexts, but particularly so in eastern North America where varying soil types and microorganisms, temperature, humidity, and moisture fluctuation interact to limit the preservation of all types ofplant parts. Carbonization is the primary process by which most archaeobotanical assemblages are preserved, and those plants with lignified cell structures stand a better chance to withstand flame than those with softer tissue. These anatomical features favor nutshell and large seeds with hard coats over tubers and wood over leaves, for example. The process of carbonization is particularly unkind to cucurbits. Both squash and Cucurbita gourd rinds are composed largely of loosely organized rows of parenchyma cells (which are soft, thin-walled, and easily warped and eroded) and outer layers of harder, thicker-walled sclerenchyma cells. Both are easily consumed by heat. Excavation and flotation of sediments further degrades carbonized archaeological cucurbit specimens. The combination ofthese factors more often than not 65 Domestication of Cucurbita pepo, Eastern Kentucky reduces archaeological Cucurbita rinds to small blackened bits that are not of much use beyond simple identification. Other parts of the plant (e.g., seeds, peduncles, rind warts, and blossom or peduncle scars) are even less frequently recovered or recognizable. Fortunately, cucurbits are also occasionally preserved in uncarbonized states in dry cave or rockshelter deposits or...