Domestication History of the Squash Plant (Cucurbita spp)

Was the Squash Plant Domesticated for its Taste--or its Shape?

Full Frame Shot Of Pumpkins And Squashes
Pumpkins and Squashes. Stephan Fenzl / EyeEm / Getty Images

Squash (genus Cucurbita), including squashes, pumpkins, and gourds, is one of the earliest and most important of plants domesticated in the Americas, along with maize and common bean. The genus includes 12-14 species, at least five of which were domesticated independently, long before European contact in South America, Mesoamerica, and Eastern North America.

Five Main Species

The designation cal BP means, roughly, calendar years ago before the present. Data in this table has been assembled from a variety of available sources, listed in the bibliography for this article.

Name Common Name Location Date Progenitor
C. pepo spp pepo pumpkins, zucchini Mesoamerica 10,000 cal BP C. pepo. spp fraterna
C. moschata butternut squash Mesoamerica or northern South America 10,000 cal BP C. pepo spp fraterna
C. pepo spp. ovifera summer squashes, acorns Eastern North America 5000 cal BP C. pepo spp ozarkana
C. argyrosperma silver-seeded gourd, green-striped cushaw Mesoamerica 5000 cal BP C. argyrosperma spp sororia
C. ficifolia fig-leafed gourd Mesoamerica or Andean South America 5000 cal BP unknown
C. maxima buttercup, banana, Lakota, Hubbard, Harrahdale pumpkins South America 4000 cal BP C. maxima spp adreana

Why Would Anybody Domesticate Gourds?

Wild forms of squashes are harshly bitter to humans and other extant mammals, but there is evidence that they were harmless to mastodons, the extinct form of elephant. Wild squashes carry cucurbitacins, which can be toxic when eaten by smaller bodied mammals, including humans. Large-bodied mammals would need to ingest a huge amount to have an equivalent dose (75-230 whole fruits at once). Interestingly, when the megafauna died off at the end of the last Ice Age, wild Cucurbita declined. The last mammoths in the Americas died off about 10,000 years ago, around the same time squashes were domesticated. See Kistler et al. for a discussion.

Archaeological understanding of squash domestication process has undergone a considerable rethinking: most domestication processes have been found to have taken centuries if not millennia to complete. In comparison, squash domestication was fairly abrupt. Domestication was likely in part the result of human selection for different traits related to edibility, as well as seed size and rind thickness. It has also been suggested that domestication may have been directed by the practicality of dried gourds as containers or fishing weights.

Bees and Gourds

Evidence suggests that cucurbit ecology is tightly bound up with one of its pollinators, several varieties of an American stingless bee known as Peponapis or the gourd bee. Ecological evidence (Giannini et al.) identified a co-occurrence of specific types of cucurbit with specifics type of Peponapis in three distinct geographic clusters. Cluster A is in the Mojave, Sonoran and Chihuahan deserts (including P. pruinosa); B in the moist forests of the Yucatan peninsula and C in the Sinaloa dry forests.

Peponapis bees may well be crucial to understanding the spread of domesticated squash in the Americas, because bees apparently followed the human movement of cultivated squashes into new territories. Lopez-Uribe et al. (2016) studied and identified molecular markers of the bee P. pruinosa in bee populations throughout North America. P. pruinosa today prefers the wild host C. foetidissima, but when that is not available, it relies on domesticated host plants, C. pepo, C. moschata and C. maxima, for pollen.

The distribution of these markers suggests that modern squash bee populations are the result of a massive range expansion from out of Mesoamerica into the temperate regions of North America. Their findings suggest that the bee colonized eastern NA after C. pepo was domesticated there, the first and only known case of a pollinator's range expanding with the spread of a domesticated plant.

South America

Microbotanical remains from squash plants such as starch grains and phytoliths, as well as macro-botanical remains such as seeds, pedicles, and rinds, have been found representing C. moschata squash and bottle gourd in numerous sites throughout northern South American and Panama by 10,200-7600 cal BP, underlining their probable South American origins earlier than that.

Phytoliths large enough to represent domesticated squash have been found at sites in Ecuador 10,000-7,000 years BP and the Colombian Amazon (9300-8000 BP). Squash seeds of Cucurbita moschata have been recovered from sites in the Nanchoc valley on the lower western slopes of Peru, as were early cotton, peanut, and quinoa. Two squash seeds from the floors of houses were direct-dated, one 10,403–10,163 cal BP and one 8535-8342 cal BP. In the Zaña valley of Peru, C. moschata rinds dated to 10,402-10,253 cal BP, alongside early evidence of cotton, manioc and coca.

C. ficifolia was discovered in southern coastal Peru at Paloma, dated between 5900-5740 cal BP; other squash evidence that has not been identified to species include Chilca 1, in southern coastal Peru (5400 cal BP and Los Ajos in southeastern Uruguay, 4800-4540 cal BP.

Mesoamerican Squashes

The earliest archaeological evidence for C. pepo squash in Mesoamerica comes from excavations carried out during the 1950s and 1960s in five caves in Mexico: Guilá Naquitz in Oaxaca state, Coxcatlán and San Marco caves in Puebla and Romero’s and Valenzuela’s caves in Tamaulipas.

Pepo squash seeds, fruit rind fragments, and stems have been radiocarbon dated to 10,000 years BP, including both direct dating of the seeds and indirect dating of the site levels in which they were found. This analysis allowed also to trace the dispersion of the plant between 10,000 and 8,000 years ago from south to north, specifically, from Oaxaca and southwestern Mexico toward Northern Mexico and the southwestern United States.

Xihuatoxtla rockshelter, in tropical Guerrero state, contained phytoliths of what may be C. argyrosperma, in association with radiocarbon dated levels of 7920+/- 40 RCYBP, indicating that domesticated squash was available between 8990-8610 cal BP.

Eastern North America

In the United States, early evidence of initial domestication of Pepo squash comes from different sites from the central midwest and the east from Florida to Maine. This was a subspecies of Cucurbita pepo called Cucurbita pepo ovifera and its wild ancestor, the inedible Ozark gourd, is still present in the area. This plant formed part of the dietary complex known as the Eastern North American Neolithic, which also included chenopodium and sunflower.

The earliest use of squash is from the Koster site in Illinois, ca. 8000 years BP; the earliest domesticated squash in the midwest comes from Phillips Spring, Missouri, about 5,000 years ago.