Y-Chromosomes and the Early Peopling of the Americas
Stephen L. Zegura

University of Arizona

In 1986 Greenberg, Turner, and Zegura published a widely cited and highly controversial paper in Current Anthropology entitled "The Settlement of the Americas: A Comparison of the Linguistic, Dental, and Genetic Evidence." My role was to provide a synthesis of all genetic information pertinent to the early peopling of the Americas. Our position paper stressed the apparent congruence of the then available data from linguistics, dental morphology, and traditional biparental nuclear genetic systems within the context of the archaeological record. Our major explanatory hypothesis, the so-called "three-wave" or "tripartite" model, was based on the proposition that all indigenous Native American populations could be allocated to three distinct groups that had their origins in three separate migrations from Asia to the Americas. The first "wave" supposedly consisted of the ancestors of the Amerind-speaking Indians currently distributed throughout the Americas. The NaDene-speaking North American Indians and the Aleut-Eskimo speakers represented the descendants of the other two "waves" whose order and chronology were unclear; however, all lines of evidence pointed to a more recent entry for these two groups than for the Amerind ancestors.

Since 1986, literally hundreds of papers have appeared from fields as diverse as skeletal biology, archaeology, genetics, linguistics, ecological anthropology, evolutionary anthropology, geology, climatology, paleontology, zooarchaeology, and bioarchaeology that have either tested or used our model. Because I am an anthropological geneticist, my presentation will emphasize what has happened in the area of genetics over the last 16 years, as well as my ongoing research on Asian and Native American Y-chromosomes. For instance, it is only the synthetic work on traditional serogenetic and protein coding loci by Cavalli-Sforza and his associates that has strongly supported our model. Neither maternally inherited mitochondrial DNA nor the paternally inherited Y-chromosome (the two haploid systems of choice today for microevolutionary reconstruction) has led to a three-wave scenario as its principal explanatory model for the early peopling of the Americas. For the record, my own views have also changed as new data and interpretations have become available adding new layers of complexity to our 1986 vision. When Joe last visited Tucson in April, 1998, we spoke at length about many of these new findings and you might be surprised at what he told me . . . then again, if you knew Joe well, you probably would not be surprised at all!