Multiple-locus departures from panmictic equilibrium within and between village gene pools of Amerindian tribes at different stages of agglomeration

Abstract

A comparative analysis of departures from multiple-locus Hardy-Weinberg equilibrium is presented for a set of four tribal Indian groups (the Yanomama, Makiritare, Wapishana and Ticuna) from the lowlands of South America. These tribes span a range of agglomeration and acculturation from the most traditional, swidden horticulturalists to frontier townspeople. The small-group social organization typical of traditional horticulturalists leads to substantial departures from tribal panmixia, as manifested by the distribution of multiple-locus genotypes both within and between villages. Within villages, the departures from single-locus Hardy-Weinberg equilibrium are small and nonsignificant, but the departures from gametic equilibrium (independence of loci) are substantial, even for the unlinked loci we have used to characterize these populations. The departures from single-locus homogeneity across villages are also substantial. One of the normal concomitants of increasing acculturation in this setting is an increase in agglomeration. As agglomeration increases, the departures from multiple-locus panmixia decrease, a process that can be very rapid. We discuss both the shifting balance theory of evolution and punctuated evolutionary rates in light of the small group social organization that must have obtained throughout most of human evolution. OR the past years, beginning with our studies of the Xavante Indians of F the Brazilian Mato Grosso (NEELet al. 1964; SALZANO, NEELand MAYBURYLEWIS1967), we have carried out a series of studies on the genetic organization 20 and social structure of South and Central American Indian tribes. The primary motivation for this ongoing research has been the belief that it should be possible to determine the extent to which the genetic organization of these human populations reflects their social organization, demography and ecology. Two aspects of genetic organization have emerged. First, the random influences on these generally small populations are sufficient to generate substantial microdifferentiation among villages within a tribe, as measured either by Fstatistics (NEELand WARD1972) or by analogous treatments (SPIELMAN, NEEL and LI 1977). This pattern of infratribal differentiation is a general finding in our studies (cf. NEELet al. 1977a,b; SALZANO et al. 1977; SMOUSE and WARD 1978),as well as in the studies of others on tribal groups from around the world Genetics 104: 133-153 May, 1983. 134 P. E. SMOUSE, J. V. NEEL AND W. …