A new DNA study by population geneticist Michael Hammer suggests that half as many men as women have contributed to the world's gene pool since the dawn of humanity.
Hammer and his research partners examined the DNA of three geographically separated groups -- the Khoisan of southern Africa, the Khalks of Mongolia and the highlanders of Papua New Guinea. More specifically, they looked at each group's Y chromosome DNA, inherited from father to son, and their mitochondrial DNA (mtDNA), inherited from mother to child. The test results showed that over the millennia, a very small group of men contributed their DNA to these populations, compared with a much larger group of women. In other words, there was more genetic diversity amongst the mtDNA inherited from their mothers than the Y chromosomes they inherited from their fathers.
This would suggest, with each passing generation, a small group of men managed to impregnate multiple women. Additionally, the reseachers found that male DNA traveled over greater distances than the female DNA, conjuring images of randy sailors on shore leave, or mysterious jet-setting men with attractive foreign accents making the rounds. More likely, they suggest, it means that women have similar criteria for what they find as suitable mates, and only a subset of men in any given generation managed to fit this criteria, so these guys took advantage of it.
I find the results fascinating, not only because it'll provide great fodder for late-night TV comics, but because the research results contrast to what was found in a similar study on Jewish populations. In that study, researchers found a rather different effect: that far fewer women have contributed their DNA to the modern Jewish population than ancient non-Jewish women did for modern non-Jewish populations. According to that research, published two years ago in the American Journal of Human Genetics, there is strikingly less mtDNA genetic diversity amongst Jewish populations than there is compared with the mtDNA found in surrounding non-Jewish communities. In fact, the study even suggests that as few as eight different sources of particular mtDNA mutations -- ie, eight different women if you go back far enough -- contributed mtDNA to these modern Jewish populations. This wouldn't mean that those eight women had a lot of children with different fathers and their female children did the same, but it suggests that at some point in Jewish history, there was a population bottleneck, and survivors with these eight mtDNA patterns managed to survive the bottleneck more successfully than others. Perhaps more men survived the bottleneck than women, as well.
This probably won't mean much to most of you, but I'm totally fascinated by this stuff. Four years ago I was one of the first guys able to get access to commercial DNA testing to participate in Professor Hammer's research, particularly in the area of Jewish males inheriting what's known in the popular press as the Cohen gene. Hammer discovered that a majority of Jewish males brought up to believe an oral tradition that their ancestors were heriditary high priests (Cohens) at the Temple of Solomon shared a common Y chromosome pattern dating from the biblical period. Meanwhile, Jewish males who were raised to believe they descended from other patrilineal lines were far less likely to carry this gene. The Torah says that the children of Aaron, Moses' brother, became the high priests of the temple, and passed it down to their sons, and Hammer's research was the first to suggest that there may be some truth to this. I was raised to believe my family came from the high priests, and indeed, my DNA test confirmed I carry the Cohen gene.
Meanwhile, my mtDNA, which I inherited from my mother, carries a pattern found less commonly in Jewish populations, and even rarer in European populations (For those of you keeping score, my mtDNA pattern, abbreviated as 126c 362c, is part of a family of mtDNA patterns called the Pre-HV1 Haplotype, in case someone asks you.) Interestingly, this mtDNA pattern of mine pops up with high frequency amongst Bedouin Arabs, Yemenis, Ethiopians and even Nubians. The only part of Europe that finds this mtDNA in any significant number is southern Spain, which of course was once dominated by an Arab population. Does this mean one of my ancestor's on my mother's side was really a Bedouin or an Ethiopian and married into a Jewish family? Maybe, but not necessarily. It's more likely that the pattern first appeared in a female ancestor of mine thousands of years before Jews or Israelites became a specific ethnic group, perhaps somewhere in the Arabian peninsula around 20,000 years ago, and eventually their descendents formed one of the tribes that became the first clans of Israelites. Unfortunately, there's no paper trail, so there's no way we'll ever really know. Makes for great cocktail conversation, though.... -andy