The phylogeny of the L2 complete sequences showed that the two mtDNAs from L2b and L2d seem disproportionately derived, compared with those from L2a and L2c. This result is not consistent with a simple model of neutral evolution with a uniform molecular clock.

The pattern of nonsynonymous versus synonymous substitutions hints at a role for selection in the evolution of human mtDNA.

Regardless of whether selection is shaping the evolution of modern human mtDNAs, the population screening of L2 mtDNAs for the mutations identified by our complete sequence study should allow the identification of marker motifs of younger age with more restricted geographic distributions, thus providing new clues about African prehistory and the origin and relationships of African ethnic groups.

References

 Torroni A, Rengo C, Guida V, Cruciani F, Sellitto D, Coppa A, Calderon FL, Simionati B, Valle G, Richards M, Macaulay V, Scozzari R. Do the four clades of the mtDNA haplogroup L2 evolve at different rates? Am J Hum Genet. 2001 Dec;69(6):1348-56. Epub 2001 Oct 10. PMID: #11595973#