Some years ago the theory was propounded, based on studies of mitochondrial DNA passed only from mother to daughter, that all humanity was descended from one woman who lived somewhere in Africa about 200,000 years BPE.
However, just yesterday we watched a program on the National Geographic channel which said that, based on Y chromosomes passed only from fathers to sons, all men were descended from a “scientific Adam” who lived about 60,000 years BPE in East Africa. The narrator consistently said all men, and not all humans, were descended from this one individual.
So…can these two ideas be reconciled, or has the “mitochondrial Eve” theory been disproved? As I see it, mitochondrial Eve could have been with a number of men to produce her descendents, and ultimately us. Y-chromosome Adam probably had a number of women in the course of his life, producing his descendants, and ultimately us. But this implies that there must have been two severe population bottlenecks, one 200000 years ago and the other 60000 years ago, when the human species was in danger of dying out. Or does it? Can anyone comment on this?
That goes without saying, but I don’t see how it reconciles with the Y-Chromosome Adam 140,000 years later. In the same way, that man’s mother would be Eve, so to speak.
Just because a certain component of the genome can be traced back to a single individual, doesn’t mean that that individual was the only person of that sex alive at the time. At the time that mitochondrial Eve was alive, there were undoubtedly many thousands of other humans alive, men and woman. Many of those individuals may have contributed to the nuclear genome, and we are descended from them in this sense, as well as mitochondrial Eve. Likewise with Y-chromosome Adam - we can demonstrate that the Y-chromosome that today’s men is descended from him, but these men, as well as today’s women, have genes on their other chromosomes descended from many other individual men who were alive at the same time.
Recall that the mitochondria are in the cell cytoplasm, and have their own genetic system separate from the nuclear DNA. The mitochondria are passed down through the maternal line because they are transmitted via the egg - sperm don’t carry mitochondria (or very, very few). The nuclear DNA carries many genetic lineages that may have originated in many other individuals.
Likewise, the Y-chromosome is transmitted almost intact from generation to generation - unlike other chromosomes, it does not undergo recombination (or very little). But there are 22 other chromosomes plus the X, and all of them can carry genetic lineages that originated in other individuals than Y-chromosome Adam.
No, mitochondrial Eve and Y-chromosome Adam have absolutely nothing to do with one another. As the research shows, they lived at very different times, and most likely in different places.
Naturally, it’s understood that there were thousands of other people living alongside ‘Eve’ or ‘Adam’. But don’t these theories still imply that only those two people left descendants who are now alive? And, come to think of it, Y-chromosome Adam would have to be a descendant of mitochondrial Eve.
No, as I said, although we may all have the mitochondria of “Eve,” that doesn’t mean some of our nuclear genes didn’t originate in other women who were alive at the same time - we are descendants of them as well. And although Y-chromosome Adam could have been a descendant of “Eve,” there is no reason he had to be. That far back in time other mitochondirial lineages could have been around that have since died out, and he could have belonged to one of them.
Suppose that in one generation, we have only three women who are alive. One of them is Eve. Eve has six children, all of them daughters. Each of the other two women has three children each, all of them sons. In the second generation, we have a population in which all of the females have descended from Eve, and all of the males have not descended from Eve. In the third generation, all children born will be born to the daughters of Eve, and will inherit her mitochondrial DNA, though each of these also necessarily had fathers who had mothers who were not Eve. Eve was not these children’s only grandmother, and the mitochondrial Eve theory does not claim that to be the case.
In the same way we have a hypothetical Adam, who had all sons, at a time when all other human males had only daughters. Adam could be any N’th descendent of Eve, did not have to mate with her, and did not have to father all of the children in the population in order to be the only source of Y chromosomes.
These examples are grossly simplified, and in reality there can be many hundreds of generations before a competing line is wiped out. But that’s the theory, anyway.