Genetic Analysis Determines Age of Y-Chromosome ‘Adam’

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The most recent common ancestor of the Y-chromosome variant present in all living human males today is referred to as “Y-chromosome Adam.” Recent genetic analysis has revealed that “Adam” lived about 208,000 years ago. Eran Elhaik from the University of Sheffield led the study and published the results in the European Journal of Human Genetics.

As a child receives one chromosome from the father (XY) and the mother (XX), the Y chromosome can only be acquired from the father. In humans, the Y chromosome is responsible for creating “maleness” because it contains the SRY gene, which has profound sex determination implications. This includes, among other things, formation of the gonad precursors that form the testes, secretion of testosterone, and hormones that shut down precursor female organs. 

Much the same way that only fathers can pass on the Y chromosome to his son, only females can provide the mitochondrial genome (though either gender can receive it). Thus, the genetic analysis seeks to find the first individuals to pass down those sex-dependent features. Playing off of the Biblical metaphor, they are referred to as “Y-chromosome Adam” and “mitochondrial Eve” as the most recent common ancestor of our species. Homo sapiens have been estimated to be about 200,000 years old, going off of fossil data. The results of this study largely fall in line with that figure, but push it back to a more definite 208,300. These results support previous research that the mitochondrial “Eve” came from approximately the same time frame. 

A study was released about a year ago that claims “Adam” lived approximately 338,000 years ago, about the time that Neanderthals appeared on the scene. If this were the case, it would mean that the Y-chromosome predates anatomically modern humans altogether. This would imply large amounts of interbreeding with other human species. However, there is no evidence in the fossil record to support this and is likely the result of poor statistical calculations and interpretations. In fact, Elhaik et al. have deemed the math in this study as so disastrous, it essentially dooms our species to a “space-time paradox” in which the oldest member of Homo sapiens wouldn’t even be born yet, based on those calculations.

There was no definite Adam and definite Eve living in a magical garden 6,000 years ago; there were likely many of these individuals occupying small nomadic groups that led the exodus out of Africa about 200,000 years ago. While there is evidence of Homo sapiens interbreeding with other human species, the full extent of how that may have influenced our genetic makeup has not yet been determined.

Read more: http://www.iflscience.com/plants-and-animals/genetic-analysis-determines-age-y-chromosome-%E2%80%98adam%E2%80%99

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