The four founding lineage hypothesis for the New World: a critical reevaluation

It has been proposed that all native American mitochondrial DNA variation in the New World can be attributed to divergence from four "founding lineages" which entered the New World in three waves of migration from across the Bering Strait (T.G. Schurr et al., 1990, Am. J. Hum. Genet. 46: 613-623; A. Torroni and D. C. Wallace, 1995, Am. J. Hum. Genet. 56: 1234-1236; A. Torroni et al., 1994, Am. J. Hum. Genet. 54: 303-318; A. Torroni et al., 1994, Proc. Natl. Acad. Sci. USA 91: 1158-1162; A. Torroni et al., 1994, Am. J. Phys. Anthropol. 93: 189-199; A. Torroni et al., 1993a, Am. J. Hum. Genet. 53: 563-590; A. Torroni et al., 1993b, Am. J. Hum. Genet. 53: 591-608; Wallace and A. Torroni, 1992, Hum. Biol. 64(3): 403-416). Torroni et al. (1993a) believe that only one haplotype from each of these four founding lineages arrived in the New World via migration, and all the additional variation arose in the New World. Any other types were attributed to Caucasian admixture. G. Bailliet et al. (1994, Am. J. Hum. Genet. 55: 27-33), N. O. Bianchi and F. Rothhammer (1995, Am. J. Hum. Genet. 56: 1236-1238), and D. A. Merriwether (1994, Experientia 50: 592-601; 1995, Am. J. Phys. Anthropol. 98(4): 411-430) suggest that multiple variants of each lineage entered the New World, and that additional unrelated lineages also entered. We present the distribution of multiple variants of the four founding lineages, plus two additional lineages which we call X6 and X7, throughout the New World, Siberia, and Asia. These distributions are strong evidence that at least nine different founding lineage haplotypes entered the New World. Further, we find these distributions among Native Americans best fit a single wave of migration into the New World.