Question about evolution, genetic bottlenecks, and inbreeding

When we discuess scientific definitions things do not always mean what they say though do they. IF they did, we wouldnt need defintions.I have found these definitions, and you are saying they do not matter. Ofcourse they matter, the are written by emininent biolgists for a reason.You can not just brush aside these defintions, there must be a way to reconcile/disprove why an individual is not guarenteed to be an MRCA at some point down the line.How do I upload pictures?

The definitions of "most" and "recent" aren't different in biology. Quote these eminent biologists. I didn't follow that. You don't. You put img tags around the internet address of the picture you want to display. If it doesn't have an internet address, upload it to an image hosting site such as ImageShack.Edited by Dr Adequate, : No reason given.

Further to my previous remarks, consider the possibility that individuals C and D lived, or reproduced, later than A, B, E, F, G and H (which is perfectly possible as generations don't go regularly like the ticking of a clock).Then they would be more recent than Adam or Eve. Adam would still be the MRCA in the male line, but not an MRCA. Eve would still be the MRCA in the female line, but not an MRCA.

quote:

---

Ok so this is my point. If we reach this point, where we have narrowed down the most recent common ancestor down to two people in our quest to find one (if my definition is correct). Plenty of others could have contribured to the gene pool, but these are the direct ancestors.

---

No. You have found TWO common ancestors. The most recent common ancestor *might* be the most recent of these two or (more likely) is another more recent individual.That is because (ignoring complications) the Y-chromosome lineage ONLY considers male-to-male (father-to-son) descent. The mitochondrial lineage ONLY considers the female line (mother-to-daughter). To find the MOST recent common ancestor we must relax those restrictions to include all lines of descent.

quote:

---

(Althought I am note sure. If the common ancestor of everyone today, had kids with only one woman as you suggest, they would both the M-Eve and Y-Adam, as they are both the most recent examples of where everyone got their chromosomes.

---

This is not true. Even if the most recent common ancestors were a strictly monogamous couple, with no other partners, it would probably be false. For the man to be a Y-chromosome Adam everybody must be descended from one of his sons. For a woman to be the mitochondrial Eve everyone must be descended from one of her daughters. But to be the most common ancestors all that is necessary is that everyone must have (at least) one of their children - son OR daughter - as an ancestor.

The could be our MCRAs without either their Y-chromosome line or their mitochondria being represented in the modern population if, just for example, the had only a single son, and then that son had only daughters (this argument applies equally to a single MCRA).

In the scenario described, who is the most recent common ancestor of S and T, according to your understanding?

You are right that A is the Y Adam to the last generation on the chart (I hadn't noticed that ).But all the first generation individuals (A -H) have descendents in the last generation so they are all ancestors to "today's" generation and they are all equally "recent". The whole population of A-H is exactly 3 generations back from S-Z. None of A-H is more recent than any others.

quote:

---

No. You have found TWO common ancestors. The most recent common ancestor *might* be the most recent of these two or (more likely) is another more recent individual.

---

Yeah sorry I worded that wrong. I will get back later tonight with a diagram to help explain what I mean

Okie kokieFirst

quote:

---

Quote these eminent biologists:

---

'Concestor 0 is the most recent ancestor that unites the geograpahically divided population' Dawkins, page 45 ancestors tale.See graph on page 49 of the book to see how ONE PERSON is the most recent common ancestor of all mankind.(I will deal with this again later)You can go on natural journals if you have access and see references.

quote:

---

However, if we consider not just our all-female and
all-male lines, but our ancestors along all parental lines,
it turns out that everyone on earth may share a common
ancestor who is remarkably recent....that the
common ancestor of everyone alive today very likely lived
between 2,000 and 5,000 years ago.

---

Douglas Rhode, On the Common Ancestors of All Living HumansIf you guys are so sure of yourself, you should be doing research yourself.Now looky here I have drawn this in response to

quote:

---

No. You have found TWO common ancestors. The most recent common ancestor *might* be the most recent of these two or (more likely) is another more recent individual.

---

If we assume the top two people on the chart are Y-adam and M-Eve, we have our two common ancestors. Now their son (their can be any period of time in between the Adam and Eve and the son I have drawn, it does not matter. However, now, say we are descended from people living in Asia. Who is the whole human races Y adam? They guy at the top, assuming his other son survived and passed on his genes and did not interbreed with the population on the chart.However who is the MOST Recent common ancestor of all the asian and african populations? Adam's skip however many generations son!Now all you need to do, is extropolate this to where one son split off to be a chimpanzee, and another split off to become humans.If anyone here can draw me a tree disproving that there must have at some point been someone who is the ancestor of all humans. I'll shut up. But I am 99% sure that a Most recent common ancestor is an individualEdited by harry, : No reason given.Edited by harry, : No reason given.Edited by Adminnemooseus, : change image to thumnail.

One point, the MCRA of both humans & chimps would also be the MRCA to any other chimpoid species (no fossils have been found as of yet) and to the hominid genera, Sahelanthropus, Orrorin, Ardipithrcus, Australopithicus, Parantropus, Kenyanthropus & Homo.source: Evolution A Scientific American Reader pg 285 b/Ian Tattersall

---

There is no better love between 2 people than mutual respect for each other WT Young, 2002Who gave anyone the authority to call me an authority on anything. WT Young, 1969Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008

quote:

---

One point, the MCRA of both humans & chimps would also be the MRCA to any other chimpoid species (no fossils have been found as of yet) and to the hominid genera, Sahelanthropus, Orrorin, Ardipithrcus, Australopithicus, Parantropus, Kenyanthropus & Homo.

---

Agreed

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.

Thats all well and good, but I am talking about the ancestors of individual creatures, not of individual genes.

quote:

---

Ok so this is my point. If we reach this point, where we have narrowed down the most recent common ancestor down to two people in our quest to find one (if my definition is correct). Plenty of others could have contribured to the gene pool, but these are the direct ancestors.

---

Disregard it, I phrased it badly and it was wrong anyway. I think my most recent post explains my position well enough.I am now saying a MRCA can not be a group of individuals and i am inviting someone to disprove me.

quote:

---

Now all you need to do, is extropolate this to where one son split off to be a chimpanzee, and another split off to become humans.

---

Presumably you mean to take the most recent male-line common ancestor of both chimps and humans. In that case the male lines of common descent for chimps and humans would lead back to different sons of this individual.But what is the point ? Once we remove the restriction of looking only at a pure male line we may find that both of the sons are common ancestors of humans and chimpanzees - and we would almost certainly
find that there were other common ancestors amongst the population of that time. The existence of common ancestors does not in itself apply bottlenecks.

quote:

---

The existence of common ancestors does not in itself apply bottlenecks.

---

Yeah I got that, staga explained it. However I am uneasy with people saying a Most Recent Common ancestor can be a group of people.Can we confirm there must a single most recent individual common ancestor to all humans? Or do we disagree on that to?