RecentAfrican origin ofmodernhumansrevealed bycomplete sequences ofhominoid mitochondrial DNAs (molecular clock/synonymous substitution rate/multiregional hypothesis/"out ofAfrica" hypothesis)

We analyzed thecomplete mitochondrial DNA (mtDNA)sequences ofthree humans(African, Euro- pean, andJapanese), three African apes(common andpygmy chimpanzees, andgorilla), andoneorangutan inanattempt toestimate mostaccurately thesubstitution rates anddiver- gence times ofhominoid mtDNAs.Nonsynonymous substitu- tions andsubstitutions inRNAgenes haveaccumulated with anapproximately clock-like regularity. Fromthese substitu- tions andundertheassumption thattheorangutan and African apesdiverged 13million years ago,weobtained a divergence timeforhumansandchimpanzees of4.9million years. Thisdivergence timepermitted calibration ofthe synonymous substitution rate(3.89 x 10-8/site peryear). To obtain thesubstitution rateinthedisplacement (D)-loop region, wecompared thethree humanmtDNAsandmeasured therelative abundance ofsubstitutions intheD-loop region andatsynonymous sites. Theestimated substitution ratein theD-loop region was7.00x 10-8/site peryear. Using both synonymous andD-loop substitutions, weinferred theageof thelast commonancestor ofthehumanmtDNAsas143,000 ± 18,000 years. Theshallow ancestry ofhumanmtDNAs,to- gether withtheobservation thattheAfrican sequence isthe mostdiverged amonghumans, strongly supports therecent African origin ofmodernhumans, Homosapiens sapiens. Light will bethrown ontheorigin ofmanandhishistory (1).