Crops take a dusting in ancient society.

One of the earliest transitions to a politically stratified society in the Americans took place not among crop growers, but among villagers who hunted, fished and gathered wild plants along Mexico's southwestern coast about 3,500 years, ago, according to a report in the February CURRENT ANTHROPOLOGY.

This finding, along with the excavation of a coastal Peruvian settlement from the same period (SN: 1/19/91, p.38), indicates that many New World coastal societies developed without relying on agricultural techniques, which anthropologists often consider essential to the growth of civilizations.

Researchers led by anthropologist Michael Blake of the University of British Columbia in Vancouver collected 1- to 2-gram bone samples from 36 human skeletons excavated from 15 archaeological sites along the west coast of southern Mexico and Guatemala. The earliest sites date to between 2700 B.C. and 1800 B.C.; the most recent date to between A.D. 1200 and A.D. 1524.

The scientists ground up each bone sample and produced a dried gelatin for chemical analysis in a mass spectrometer. Ratios of specific carbon and nitrogen isotopes in bone signify the regular consumption of particular classes of agricultural and wild plants, as well as fish and other sea creatures.

Blake's group focused on 16 bone samples taken from "early formative" villagers, who lived in sites in southwestern Mexico from around 1550 B.C. to 850 B.C. Early formative people in Mexico transformed isolated outposts into chiefdoms, with a ruler presiding over politically united villages, the researchers contend.

Previous excavations documented the presence of large settlements, extensive public buildings, elaborate ceramics and figurines, and imported obsidian at early formative sites by approximately 1350 B.C.

Bone analyses indicate that early formative diets revolved primarily around fishing and gathering of wild plants, the researchers note. Carbon and nitrogen values suggest the villagers consumed "very limited" amounts of maize and related agricultural crops.

Excavation of refuse pits at the Mexican sites provides as more specific inventory of the early formative diet, the investigators note. The menu included several types of freshwater fish, turtles, crocodiles, iguanas and snakes. Remains of white-tailed deer and many other land mammals and birds were also found in the ancient dumps, suggesting considerable hunting.

From 850 B.C. through the first millennium A.D., maize assumed more prominence in the diets of coastal villagers, although the basic hunting-fishing-gathering approach persisted, Blake's group asserts.

Bones from coastal Guatemalan sites reveal the greatest reliance on agricultural crops, which may help explain why those settlements grew larger than the ones 60 miles north in southwestern Mexico.