Mother of Eve (was Re: [asa] Two questions... (biological bottlenecking with Adam and Eve))

Hi Bernie,

The answer to your question might be more evident if we use the less prosaic name for mitochondrial eve, i.e. matrilineal most recent common ancestor (MRCA).

The point is simply that if we trace back the matrilineal lines of descent for all living humans we arrive at some point at a single matriarchal line. And the individual at which all matriarchal lines converge is the MRCA.

The MRCA of all humans is not, necessarily, herself human - as a forced example one could attempt to trace the MRCA for two separate species - say cat and dog. In such a case the MRCA would obviously not be a member of either species.

Obviously the MRCA herself had a mother - but by definition her mother could not be the _most recent_ common ancestor.

Hope it helps,
Murray

Dehler, Bernie wrote:
> Hi Dr. Campbell-
>
> I having a hard time understanding why this argument seems to be going in circles.
>
> Again I ask, because I don't see a clear answer (the problem may be on the sender or receiver side), how can anyone trace something back to "the first human?" For example, if someone says everyone today can be traced back to a mitochondrial eve, tell me how mitochondrial eve's mom is different, in that someone could say mitochondrial eve is the first human female but her mom isn't? I really don't get it, but I want to. (And I'm talking only biologically- not spiritually- this is a purely scientific question related to the human genome.) To me it seems like someone is proposing that an apelike creature gave birth to a human, and I don't understand that- given the ring species phenomenon.
>
> Here's a modern example of ring species, since you said you weren't aware of modern living examples (with the seagull):
> http://en.wikipedia.org/wiki/Ring_species
>
> Dr. Zack Moore talked about this on his evolution 101 podcast:
> http://www.drzach.net/podcast.htm
> (Free download at Apple iTunes; Apple iTunes is also free and you can listen on your PC)
>
> Again, I'm talking only biologically- not spiritually- this is a purely scientific question related to the human genome. It seems like the confusion comes in when talking about the spiritual element of humans, which has nothing to do (at all) with my question (which is purely biological).
>
> You say below:
> "They key problem is what all are humans?"
>
> Exactly my point. When someone claims there is a mitochondrial eve, they are saying that it is the first human- how is that defined such that mitochondrial eve's mom is not human? Obviously, mitochondrial eve is related to her mom!
>
> I have a hard time accepting your hypothetical analogy with Noah, because we both know it isn't true- there was no worldwide flood in our opinion. It is like using the old analogy of a frog in a pot that is brought to boil- bad illustration because it isn't true. I don't see how a goofy story can be used to illustrate something scientifically. It could be like if I believe that people could fly if they knew the secret- giving an analogy of santa's flying reindeer to illustrate the point.
>
> Maybe the big mistake here is in thinking that mitochondrial eve is the first human- which science says is not the case. Rather than defending how one person can be the parent of all humanity, maybe the thing you should be doing is explaining how, instead, evolution happens in populations and not through a single founder?
>
> ...Bernie
>
> -----Original Message-----
> From: David Campbell [mailto:pleuronaia@gmail.com]
> Sent: Thursday, February 12, 2009 3:04 PM
> To: Dehler, Bernie
> Cc: asa@calvin.edu
> Subject: Re: [asa] Two questions... (bottlenecking)
>
> <<<Bernie: Snipped- just the questions I'm interested in are captured below for context.>>>
>
>
>> Everything comes from something else. If you say there is a single ancestral pair from which all humans came from, what would that entail? The change of 1 gene? The change of 100's of genes? What could be the biological change where you say the parent is nonhuman but the child is human?<
>
> It might not entail anything unique genetically. They might have had
> identical twins, but they just happen to be the ones to which all
> modern lineages trace back.
>
> Where to recognize the first humans (meaning spritually accountable)
> is not necessarily the same as where the single ancestral pair is. If
> the first humans included more than a single pair (seems likely but
> not absolutely provable, given the problem of identifying the first
> humans). Under an "insert the soul"-type model, there might be no
> physical or genetic difference. If having spirituality reflects the
> arrival at a threshold level of mental capacity, then presumably there
> is some degree of genetics underlying it, although environment plays a
> role as well. The genetic difference might be quite subtle, however.
> The only case in which a line can easily be drawn between parent
> species and new species is when there is an instantaneous barrier to
> interbreeding. For example, in Glenn Morton's scenario, the
> chromosome fusion that distinguishes humans from apes plays a key
> role. Chromosome fusion (or other chromosome rearrangement) makes
> interbreeding difficult. Not directly applicable to the human case,
> but hybridization in which the hybrid can reproduce (asexually and/or
> sexually with other hybrids) but not with either parent is the easiest
> way to clearly make new species abruptly. It's common in the wild and
> in lab. However, only in hindsight can you tell that a given change
> is key to something new rather than an individual aberration. (This
> is also a problem with all the "how come we don't see new stuff
> evolving today?" type arguments. We probably are, but we can't know
> until we wait millions of years or so to see what happens next.)
>
>> In addition, I'm thinking of a presentation I heard on "ring species." A animal (such as a seagull) can have many changes as you follow the geography, with the head of the line being so different from the tail that they are called different species because they can't interbreed. However, all the in-between varieties are interbreeding along the way. If you look at just the head and tail, you'd say they are different species, but if you look at the line you can't tell where one species begins and another ends. Apply that to human biological evolution.<
>
> I don't know of evidence for a geographic ring, but there is something
> similar going through time in humans. Homo habilis is fairly
> different from modern humans, but when you put in a full set of
> intermediate fossils, it's hard to draw firm lines.
>
>> All this makes it impossible for me to accept a single biological pair for all humans. <
>
> They key problem is what all are humans?
>
>
>> Also the thing I don't understand about mitochondrial eve- what about her mom? What was so different about her mom... didn't she have mitochondria or how was it so different that there's some sort of break in which you can call her daughter the eve but not the mom?<
>
> Here's an example. Suppose, for purpose of the example, that all
> modern humans descend from Noah. Noah would be the Y-chromosome Adam
> in this scenario-some male descendants of each of the sons have sons,
> and so forth. Noah's Y chromosome might not be any different from his
> father's, but Noah is the most recent common ancestor. Automatically,
> there is a single Y chromosome ancestor in every generation before
> that. Noah's sons' wives would provide three mitochondrial
> lineages-Mrs. Noah's mitochondria die out with the death of her sons.
> The three wives share a common maternal ancestor at some point, if you
> go back far enough. If they were sisters, their mother would be
> mitochondrial Eve. On the other hand, if Shem had sons but no
> daughters, then one of the three mitochondrial lineages would be lost.
> If only one of the three couples had daughters, then that wife would
> be the mitochondrial Eve.
>
> Thus, being the mitochondrial Eve or Y chromosome Adam does not
> guarentee being the spouse of the other, nor does it guarentee that no
> other individuals lived at the time. It does tend to suggest a
> relatively small population (either at the time when they lived or in
> some sort of later bottleneck-i.e., only the descendants of a certain
> individual happen to make it through).
>
>
>

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Received on Fri Feb 13 17:40:21 2009