Village and Tribal Genetic Distances among American Indians, and the Possible Implications for Human Evolution

Abstract

Abstract. Pair-wise genetic distances based on six genetic systems (Rh, MNSs, Kidd, Duffy, Diego, and haptoglobins) are presented for seven villages of Makiritare Indians, seven villages of Yanomama Indians, and 12 Indian tribes of Central and South America. It is shown that the mean genetic distance between Indian villages is 85-90 per cent of the distance between tribes. Since in the past, the initial event in the formation of a new tribe was probably the breaking away of one or several related villages from an established tribe, it is clear that this initial event could have profound consequences for subsequent tribal gene frequencies. By the criterion of changes in gene frequency in polymorphic genetic systems, the maximal rate of evolution in the American Indian has been approximately 100 times more rapid than the mean rate suggested by calculations based on amino acid substitutions in certain polypeptides of a variety of organisms. The above-mentioned findings could account in part for this 100-fold difference. Some other factors which might diminish the apparent difference between the results of these two types of calculations are mentioned.

Extensive mitochondrial diversity within a single Amerindian tribe.

“…This study of mitochondrial sequence diversity within a tribal population confirms at the molecular level the previous finding (8) that tribal groups can contain a substantial proportion (up to 60-80%) of the genetic variability that exists within much larger regional and continental populations. The Proc.…”

“…These interpretations imply that small tribal groups-the primary demographic units of early human populations-contain only limited amounts of molecular diversity. However, such a conclusion runs counter to the observation that, for standard genetic markers, the amount of genetic differentiation within tribes represents an appreciable fraction of the genetic variability contained within continental populations (8).…”

“…The observation of extensive sequence divergence between Nuu-Chah-Nulth lineages extends to the molecular level the finding that an appreciable proportion of human genetic variability is maintained within tribal populations (8). By contrast, the available data from surveys ofrestriction site polymorphisms in other vertebrate species indicate only moderate amounts of mitochondrial diversity within local populations (29).…”

Genetic Variation Among Vertebrate Species

“…In terms of the distance function of Cavalli-Sforza & Ed wards (9), the mean pair-wise genetic distance between seven Makiritare villages is 0.356, and that between seven Yanomama villages is 0.330 (79). Since the mean pair-wise distance between Indian tribes of Central and South America is 0.385 (49), it is apparent that intra tribal variation is almost as great as intertribal. The complex of factors responsible for intra tribal differentiation includes the founder effect, genetic drift, cleavage of villages along familial lines, nonrandom patterns of in tervillage migration, and differential fertility in a polygynous mating system (ll).…”

The Population Structure of an Amerindian Tribe, the Yanomama

“…In the case of a dissident group we encountered among the Xavante (Sebastiao's band), the group had already in a single generation moved at least 200 miles when encountered by ourselves (38). It is quite clear that the allelic frequencies of a new tribe will often at the outset depart substantially from those of the tribe of origin; the potential magnitude of stochastic processes in determining the allelic frequencies of newly arisen tribes has not been heretofore appreciated (48).…”