Image: Ton Koene/Corbis
Dramatic news this week showing how, when humans diverged out of Africa they encountered many new environments and quickly diversified into them. The record of this has been found in the Y chromosome, which males uniquely inherit from their fathers. Females inherit two X chromosomes, one from each parent so it is impossible to say from which unless you have the parents' genome too. Males inherit their Y chromosome from their father and an X chromosome from their mother. For this reason the Y chromosome represents the history of the male line.
Researchers David Poznik and Carlos Bustamante and their colleagues of Stanford University found that within the space of about 150 years, some 50,000 years ago, a single site on the Y chromosome mutated to form two distinct male lines, followed very quickly by a second mutation at the same site creating a third line. These three lines can still be traced in the modern Euro-Asian populations.
It is believe the mutation occurred probably in the Arabian peninsula:
That area of the Y tree describes the crucial period when modern humans began going global, sometime after they left Africa between 70,000 and 50,000 years ago. The earlier family tree showed that the three major Eurasian genetic groups that survive today emerged from those pioneering migrants, who were probably living in the Arabian peninsula. But exactly how the ancestors of those three groups relate to one another, and how quickly they diverged after leaving Arabia was not resolved.We know that at least one branch of this evolving human tree came into contact with, and interbred with, Neanderthals but so far Y chromosome analysis has failed to find any individual who inherited his Y chromosome from a Neanderthal father. This of course could mean that these are very rare and so have not been found yet. The possibility of them being found still exists however especially since evidence emerged recently that some humans may well be carrying Y chromosomes from an extinct species of human.
Michael Hammer at the University of Arizona in Tucson and his colleagues identified a Y chromosome unlike any other in a small group of people who can trace their roots back to Cameroon.If confirmed this will be the second example of diverging and evolving humans forming a ring species, or a species in transition between an ancestor and several descendant species, much to the consternation of creationist pseudo-scientists who continue to insist, in the face if contrary evidence, that there is no evidence for human evolution nor of transition between an ancestral and a descendant species. Once again we find that creationism is not supported by real-world evidence and is refuted by science.
It is so different from any other Y chromosome so far found that it may actually have entered the modern gene pool via an ancient human that lived in western Africa, says Bustamante. "It might be our first glimpse of archaic interbreeding within Africa."
It may be the second example of a new species of Homo being discovered in the genetic record or modern humans. Recently scientists at the Max Planck Institute for Evolutionary Anthropology identified evidence of the DNA of an unknown Hominid in modern humans. This probably become incorporated into the modern human genome in addition to that of Neanderthals and the newly-discovered 'Denisovans' when humans appeared to form a ring species in Euro-Asia as Homo sapiens coming out of Africa came into contact with the descendants of their common ancestor, H. heidelbergensis who had migrated out in an earlier wave and had diversified into Neanderthals, Denisovans, and probably at least one other subspecies as they spread out into Europe and Asia.
See also A Human Ring Species? and More Evidence For A Human Ring Species
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