Stable gene scene in ancient America.

Indians who occupied part of central Florida from about 8,000 to 7,000 years ago possessed surprisingly little genetic diversity, according to a preliminary analysis of DNA extracted from some of their shriveled, preserved brains.

If further work confirms this finding, it may suggest that the Florida group and other ancient settlers of the Americas avoided breeding with neighboring tribes, contends medical microbiologist William W. Hauswirth of the University of Florida College of Medicine in Gainesville. This practice would have produced genetic stability across generations that may now render the tracing of their ancestry through analysis of ancient DNA "relatively easy," Hauswirth asserts.

From 1984 to 1986, investigators removed the skulls and other skeletal remains of 177 individuals from a Florida peat bog that had apparently once served as a burial ground. In addition, scientists discovered that the watery bog had kept 91 brains remarkably well preserved, and they began successfully to remove DNA from the ancient tissue (SN: 11/8/86, p. 293).

Since then, radiocarbon dating of samples of peat and bone taken from the prehistoric cemetery indicates that the site was used for more than 1,000 years and may contain members of as many as 50 generations, Hauswirth maintains.

He and his colleagues isolated and copied samples of nuclear DNA (inherited from both parents) and mitochondrial DNA (inherited from the mother) from 13 ancient brains. The scientists studied a specific section of the mitochondrial DNA that changes rapidly through random chemical substitutions.

A comparison of the samples reveals few differences in the chemical organization of the nuclear and mitochondrial DNA of the 13 individuals, at least so far, Hauswirth says.