MITOCHONDRIAL-DNA CLOCK FOR THE AMERINDS AND ITS IMPLICATIONS FOR TIMING THEIR ENTRY INTO NORTH-AMERICA

Students of the time of entry of the ancestors of the Amerinds into th e New World are divided into two camps, one favoring an ''early'' entr y [more than approximately 30,000 years before the present (YBP)], the other favoring a ''late'' entry (less than approximately 13,000 YBP). An ''intermediate'' date is unlikely for geological reasons. The corr elation of the appropriate data on mtDNA variation in Amerinds with li nguistic, archaeological, and genetic data offers the possibility of e stablishing a time frame for mtDNA evolution in Amerinds. In this pape r, we estimate that the separation of the Chibcha-speaking tribes of C entral America from other linguistic groups/nascent tribes began appro ximately 8000-10,000 YBP. Characterization of the mtDNA of 110 Chibcha speakers with 14 restriction enzymes leads on the basis of their time depth to an estimated mtDNA nucleotide substitution rate for Amerinds of 0.022-0.029% per 10,000 years. As a first application of this rate , we consider the mtDNA variation observed in 18 Amerind tribes widely dispersed throughout the Americas and studied by ourselves with the s ame techniques, and we estimate that if the Amerinds entered the New W orld as a single group, that entry occurred approximately 22,000-29,00 0 YBP. This estimate carries a large but indeterminate error. The mtDN A data are thus at present equivocal with respect to the most likely t imes of entry of the Amerind into the New World mentioned above but fa vor the ''early'' entry hypothesis.