Toward a more accurate time scale for the human mitochondrial DNA tree

Area of Science:

• Genetics
• Anthropology
• Evolutionary Biology

Background:

• Estimates for the most recent common mitochondrial DNA (mtDNA) ancestor of modern humans vary.
• Previous estimates using noncoding regions were older than those from codon third positions, suggesting rate heterogeneity.

Purpose of the Study:

• To reconcile discrepancies in mtDNA ancestor age estimates.
• To refine the estimation of the most recent common mtDNA ancestor's occurrence.
• To estimate the timing of modern human expansion out of Africa.

Main Methods:

• Classifying mtDNA sites into three categories: highly variable, moderately variable, and invariable.
• Utilizing partial control region sequences to account for heterogeneity.
• Calibrating the molecular clock using the estimated divergence time of humans and chimpanzees (4 million years ago).

Main Results:

• The most recent common mtDNA ancestor of modern humans is estimated to have occurred 211,000 +/- 111,000 years ago.
• This estimate aligns with previous findings from codon third positions and other studies.
• The expansion of modern humans out of Africa is estimated to have occurred 89,000 +/- 69,000 years ago.

Conclusions:

• The refined estimates provide a more robust timeline for early human evolution.
• The findings support an out-of-Africa model for modern human origins.
• The large standard errors necessitate cautious interpretation but allow rejection of the multiregional hypothesis.