MOLECULAR EVIDENCE OF HUMAN ORIGINS—[PART II]

ries appeared in the April issue. Part II follows below and continues, without introductory comments,where the first article ended.] The molecular evidence clearlydem-onstrates that mitochondrial Eveis not the “most-recent common ancestor of all humans on Earth today.” The reality is that one of the most critical assumptions behind such a concept has nowbeendisproved.MitochondrialDNA isnot exclusively received fromthemater-nal side—researchers now know that a fa-ther’smtDNAcancross into the egg.But what about the second assumption—that mutationsoccurat constant rates? BROKEN MOLECULAR CLOCKS Researcherswhomade the initial an-nouncementaboutEvenotonlygave a location for this amazing female, but al-so proposed the time period during which she was supposed to have lived. However, inorder for themtDNAtheory tobeofany practical use, those scientists had to assume that randommutations in the DNA occur-red at documented, steady rates. For exam-ple, if they speculated that there was one mutation every 1,000 years, and if they foundadifferenceof10mutationsbetween us and our ancient hypothetical ancestor, they then could infer that that ancestor lived 10,000 years ago. Scientists—who use this concept to determine the age of mito-chondrialEve—refer to this proposedmu-tation rate as a “molecular clock. ” One groupof researchersdescribed theprocess as follows: Thehypothesisof themolecularclock of evolution emerged from early ob-servations that the number of amino acid replacements in a given protein appeared tochange linearlywith time. Indeed, if proteins (and genes) evolve at constant rates, they could serve as molecular clocks for timingevolution-ary events and reconstructing the ev-olutionary history of extant species (Rodriguez-Trelles, et al., 2001, 98:11405, parenthetical iteminorig.)