Mitochondrial Eve and Chromosomal Adam may have existed at the same time

ImageHuman evolutionary geneticists  use DNA passed only through the female line, mitochondrial DNA (mtDNA), or male line, the Y chromosome, to make estimates about the last common ancestor for all living humans. Earlier work suggested that the most recent common male ancestor lived 35,000 to 190,000 years AFTER the most recent common female ancestor. Poznik et al. in this week’s Science report the results of sequencing 9.9 million base-pair length of the Y chromosome from 69 men from across the globe.  Their data suggests that the Y chromosomal Adam existed between 120 and 156 thousand years ago, much closer to the estimate for the mtEve betwen 99 and 148 thousand years ago.  Why did this study move Adam’s birthday back so much?  Well, there have been lots of technical difficulties in reconstructing the sequence of the Y-chromosome, but this research group was able to deal with some of those difficulties and use much more of the Y chromosome.  This deeper sequencing allowed the researchers to identify more variation among Y chromosomes.  Linking these differences to well-dated events in human migration (e.g. peopling the Americas), the researchers were able to make a better estimate of Y chromosome mutation rates.  As always, the researchers did have to make certain assumptions in their models of mutation rates (which I’m sure will be explored by other researchers), their approach seems robust.  Dating the most recent common male and female ancestors to essentially the same time period should reduce some of the mental gymnastics that paleoanthropologists having been doing to explain why the male ancestor lived relatively recently.  In addition to moving the most recent male ancestor further back in time, this approach to the Y chromosome has also unearthed a greater amount of diversity than was known among Y haplotypes.  Further work using this methodology should help human evolutionary geneticists male migration with more accuracy.

Y chromosome analysis moves Adam closer to Eve

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