| Research Abstract |
We analyzed the complete mitochondrial (mt) DNA sequences of three humans (African, European and Japanese), three African apes (common and pygmy chimpanzess, and gorilla), and one orangutan in an attempt to estimate most accurately the substitution rates and divergence times of hominoid mtDNAs. Nonsynonymous substitutions and substitutions in RNA genes have accumulated with an approximately clock-like regularity. From these substitutions and under the assumption that the orangutan and African apes diverhed 13 million years ago, we obtained a divergence time for humans and chimpanzees of 4.9 million years. This divergence time permitted calibration of the synonymous substitution rate (3.89_x 10^<-8>/site/year). To obtain the substitution rate in the D (displacement)-loop region, we compared the three human mtDNAs and measured the relative abundance of substitutions in the D-loop region and at synonymous sites. The estimated substitution rate in the D-loop region was 7.00_x 10^<-8>/site/year. Using both synonymous and D-loop substitutions, we inferred the age of the last common ancestor of the human mtDNAs as 143,000? B118,000 years. The shallow ancestry of human mtDNAs, together with the observation that the African sequence is most diverged among humans, strongly supports the recent African origin of modern humans, H.sapiens sapiens.
|
