Question about evolution, genetic bottlenecks, and inbreeding

The direct ancestors of what? You need context. Mit-Eve is the MRCA for all of our mitochondria. Y-Adam is the MRCA of our Y-chromosome. In fact, every single allele has it's own MRCA. As one example, there are hundreds of DRB1 alleles in the human population. It has been suggested that the MRCA for the DRB1 allele existed 60 million years ago.**************************************************
Science. 1995 Dec 22;270(5244):1930-6.
Comment in:
Science. 1996 May 31;272(5266):1363-4.
Science. 1996 Nov 29;274(5292):1552-4.The myth of Eve: molecular biology and human origins.
Ayala FJ.
University of California, Irvine, USA.It has been proposed that modern humans descended from a single woman, the "mitochondrial Eve" who lived in Africa 100,000 to 200,000 years ago. The human immune system DRB1 genes are extremely polymorphic, with gene lineages that coalesce into an ancestor who lived around 60 million years ago, a time before the divergence of the apes from the Old World monkeys. The theory of gene coalescence suggests that, throughout the last 60 million years, human ancestral populations had an effective size of 100,000 individuals or greater. Molecular evolution data favor the African origin of modern humans, but the weight of the evidence is against a population bottleneck before their emergence. The mitochondrial Eve hypothesis emanates from a confusion between gene genealogies and individual genealogies.
**************************************************(NOTE: other scientists have suggested that the 60 million date is way off)What you need to keep in mind is that mitochondria and the Y-chromosome are passed on as units. The Y-chromosome does not recombine with other chromosomes during meiosis like the autosomal chromosomes do. Therefore, mitochondria and the Y-chromosome can be treated like really big alleles.As for the common ancestor of two species, this is a different concept. In this case the context is shared DNA. The common ancestor of two species was a population that contained, at minimum, the DNA shared by the two species. Of course, no single organism in a population can carry the variability of a whole population.Edited by Taq, : No reason given.

Then let's use you and your cousins as an example. You share a common ancestor--your shared set of grandparents. For you and your cousins, your grandparents are your most recent common ancestor. However, you and your cousins carry DNA from ancestors other than your most recent common ancestor. Being that humans are dioecious, it would seem that it is impossible for ONE person to be the common ancestor of an entire species. This is possible in a bacterial colony, but not so much for humans.

I was thinking more in terms of genetics. Yes, I can see in those terms that it is not impossible.Genetically, the two groups would not share a common X chromosome ancestor that is the single male ancestor, which is what I was going for.Edited by Taq, : No reason given.

The one problem with the chart is that it assumes the all the other lineages will die off. It's not as if one son goes to Asia and finds the continent full of women and no men. It's not as if I can have two sons by two mothers, send one to Africa and one to Asia, and then proclaim myself the common ancestor of all humanity.At each point in time there may very well be a single MRCA, but that MRCA will change through time as lineages die off. Surely, the MRCA 100,000 years ago was different from the modern MRCA.

They may converge on one person, but they also have ancestors that are not common to both, ancestors that predate the MRCA. For every MRCA there are also many ancestors that are not common to everyone. There were women alive during Mitochondrial Eve's lifetime, and it is very probable that people today carry genes from those women. The same for Y Adam.

Not to brag, but the reply you got is almost the same as my reply in Post #57. Can I now consider myself an eminent biologist?

That seems to be tautological. To rephrase it, you are saying that we have a common ancestor in common.In addition, we do not all share the same MRCA's. Me and my siblings share a very recent common ancestor (our parents) that you do not share with us. The same for you and your siblings, if you have any.For any group of people there will be an ancestor that they all share, and one of those ancestors will be the most recent by definition. However, this MRCA can be different for different groups.And just in case . . . Perhaps this is what you meant to say and I am suffering from a lack of reading comprehension.

I happened to watch "Neanerthal Code" on the National Geographic Channel list night and it prompted a question that someone might be able to answer. Don't worry, it relates to the topic.One of the theories that attempts to explain the disappearance of the neanderthals is the assimiliation theory. That is, neanderthals and anatomically modern humans interbred and the neanderthal genes were diluted in the modern human population. If this is so, then shouldn't we be able to find a mitochondrial lineage in the human population? More importantly, could there be a person out there right now that is carrying mitochondria from this neanderthal lineage?The reason I ask this is that the Mitochondrial Eve study was based on a cross section of the human population. Given the technological limits it is understandable that they didn't sequence 3 million mitochondrial genomes to cover just 0.5% of the population. If only 1 in every million people carry neanderthal mitochondria there's a pretty good chance it would have been missed, or so it would seem. Are my concerns unfounded? Am I smoking crack?