Scientific Adam and Eve

[robvalue]

Speciation would be a particular point in time, yeah. But this Adam and Eve are not the points of speciation, they are the most recent common ancestor of all currently living humans, under two different rules. Which particular people are Adam and Eve is not fixed, but depends on who is still alive. If a whole bunch of people got wiped out, then they might both move "forward" to much more recent people.

Sometimes different species can reproduce, but the results are sterile. I don't know enough to say exactly why that is. So a mule is an offspring of a male donkey and female horse. They are different species so the result is sterile. It does sound like a "safety mechanism" of sorts. I've heard of Ligers too

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[Anomalocaris]

I hope no one thinks that I would try to sneak in some kind of backwards reasoning for Adam and Eve. When I learned about it, I was just shocked that scientist can link our genes back to a single man and woman. Not saying that the theory is that they were the only man and woman. And that they even lived together. However this article http://www.nature.com/news/genetic-adam-...me-1.13478 says that they could have lived concurrently. And Its interesting to me that Adam (according to the article) more than likely lived farther back than Eve. The scientific Adam and Eve that is. Could someone just explain how at one point the genes were only from a single man and a single woman? I have read the wiki pages but they're just above me  

The key is your genes are NOT from a single man or a single woman at the point when the supposed adam or eve lived.    All of us have at least some genes that derive that single man or that single woman.   But none of us, tracing our genetic history all the way back to the time of the suppsed adam or eve, can trace ALL of our genes to them.

Think of the primordial Adam and Eve as your great grand father on your father's father's side, and your great grand mother on your mother's mother's side.   You and your siblings, and many of your cousins and neices and nephews, and many of your more extended family would all share these same Adam and Eve as you.   but they are not your only male and female ancestors at their respective generations.

So they are each the last common ancester to us all, but not the only ancester to us for their generation.   What is more interesting is there must have been earlier common ancestors.   But the last common ancester does not even need to have been a direct descendant of some of the earlier common ancestors.

So Adam and Eve analogy, while cute, fails miserably at every level.

[Alex K]

I read an article that I linked in a different post on this thread that its plausible that they could have lived at the same time.

Given the ranges, it seems unlikely - and there is no logical necessity that they should have. But even if they had lived at the same time, they don't even need to have met.

And please correct me if I am wrong, but I thought that speciation was the point where an evolutionary line did branch out on its own? Wouldn't this be a clear distinction in the space time continuum? ok, I don't know what that last part was supposed to mean, I just want to sound smart too :/

I am nothing close to a speciation expert, but if the branching out happened because a small subpopulation suddenly became isolated from the rest, then I'd say you have a clear cut date. If it is sympatric, and a sub-population drifts away from the rest while still living in the same place (but probably occupying a different ecological niche) it might be more subtle, with cross-breeding fertility between the two groups going down continuously. Of course at some point may be the last time when members of the two groups interbreed, but at that point, the groups might already be quite separate. But again, IANAB.

Why are mules for example sterile? I believe the same went for Ligers, which are real! Does evolution have a safety mechanism that keeps us equal but separate?

Darwin already writes about this in "Origin" taken from his experiments with plants. I suppose fertility simply goes down when inbreeding because harmful mutations in one set of chromosomes can not be compensated by a new intact second set from the outside any more, and there will be less and less viable embryos produced.

[Clueless Morgan]

Anthropologists like to use the term "mitachondrial Eve" to describe the common female answer

I think surely there must be more than one though. I can't see how "modern humans" just emorged fully formed at one point, it had to be a gradual transition. Therefore, there was no point in history where there was ever a "first human" or a last ancestor who definitely wasn't human. There are probably several humans who all people descend from, if there's just one male and one female that basically means we're all interbred.

That reads a bit confused. She is defined as the unique individual who is the latest common female ancestor of all currently living humans *in a purely maternal line*. And while we are inbred in a certain sense because we probably all originate from some organism 3 billion years ago or so, there were never just 2 humans - as long as we were anything close to humans, the population size never dropped below several thousands. This is what analysis of the human gene pool tells us

My understanding of Mito-Eve is that she is the human to whom we can trace the mitochondrial mutations that we all currently share.  In other words, when she was born of her mother, she was born with certain mutations in her mtDNA that were unique to her, and that is what scientists can trace our mutations back to, hence why we can pinpoint a specific person as being our Mito-Eve.  We don't know exactly who she was, exactly when she lived, or even much about her, but we are reasonably certain that this one person existed and that she is the individual who happened to be the one whose mtDNA has persisted among the human species.

The same with Y-Adam.

I read an article that I linked in a different post on this thread that its plausible that they could have lived at the same time.

It's possible, but not necessary.  mtDNA is passed from mother to child and can be traced back through the female ancestral lineage.  The Y chromosome is passed from fathers to sons and can only be traced through the male ancestral lineage (since a woman only donates an X chromosome with her egg).  It's not necessary that Mito-Eve and Y-Adam live at the same time, and not necessary that they met, had sex or produced offspring.  It might not even be the case that Y-Adam be a descendant of Mito-Eve since we're talking about the lineage of two different aspects of our genome.

And please correct me if I am wrong, but I thought that speciation was the point where an evolutionary line did branch out on its own? Wouldn't this be a clear distinction in the space time continuum? ok, I don't know what that last part was supposed to mean, I just want to sound smart too :/

Speciation is very hard to put a pin in as to when it occurs; it's more of a concept than a precise moment in time.  As I said before, it's similar to looking at the electromagnetic spectrum and assigning a specific wavelength to when "green" ends and "blue" begins.  There is no clear dividing line, there's a spectrum of definitely-green to definitely-blue with a lot of sorta-greens and sorta-blues and lots of blue-greens and green-blues in the middle.  We know that there is a difference between green and blue, but we can't say exactly where that transition occurs.  It's kinda like this:



There is no single moment in time when you have a Homo erectus giving birth to a Homo sapiens; our delineation of species into kingdoms, phyla, classes, orders, families, genuses and species are taxonomic categorizations that we, humans, impose on the biological world.  The reason creationist harp on about "no transitional fossils" is precisely because there is no hard line between one species and its parent or daughter species.

Why are mules for example sterile? I believe the same went for Ligers, which are real! Does evolution have a safety mechanism that keeps us equal but separate?

Well, mules are sterile because of a chromosomal mismatch (though not all mules are sterile, just most).  Horses have 64 chromosomes and donkeys have 62, meaning a mule (the resulting offspring of a female horse and a male donkey) as receiving 32 chromosomes from its mother and 31 from its father, which leaves one chromosome without a match and ends up screwing up the fertility of the mule.

A female liger can often be fertile, while the male is sterile, so it's not all that similar to mules, which are predominantly sterile with the occasional fertile offspring.  Don't know why.  It could be due, simply, to the genetic distance from each other, but I don't really know.

Here's a freaky thought: Humans and chimps are closer, genetically, than tigers are to lions.  Could we interbreed with a chimpanzee and produce viable offspring?  

[Alex K]

@CM,

So are you saying I'm not completely wrong then? I'm not sure whether you quote me to disagree on a specific point or to elaborate further

Concerning human chimp hybrids, my unevidenced gut feeling is that it would eventually work because of what you say. I am so curious about the result of that, but at the same time know that it would not be a good idea.

[Regina]

That reads a bit confused. She is defined as the unique individual who is the latest common female ancestor of all currently living humans *in a purely maternal line*. And while we are inbred in a certain sense because we probably all originate from some organism 3 billion years ago or so, there were never just 2 humans - as long as we were anything close to humans, the population size never dropped below several thousands. This is what analysis of the human gene pool tells us

My understanding of Mito-Eve is that she is the human to whom we can trace the mitochondrial mutations that we all currently share.  In other words, when she was born of her mother, she was born with certain mutations in her mtDNA that were unique to her, and that is what scientists can trace our mutations back to, hence why we can pinpoint a specific person as being our Mito-Eve.  We don't know exactly who she was, exactly when she lived, or even much about her, but we are reasonably certain that this one person existed and that she is the individual who happened to be the one whose mtDNA has persisted among the human species.

The same with Y-Adam.

Ok this makes more sense, I didn't consider the "genetic mutation" angle of it, I was thinking more in terms of evolution being too slow to suddenly pump out a new species in one generation.

[robvalue]

Eve is a mutant bitch then. I knew it!

[Alex K]

Maybe we should distinguish between the definition of mitochondrial Eve (latest common female line ancestor) and how it is determined when she lived (strains of mtdna mutations)?

[FatAndFaithless]

I really really like that color-changing paragraph that CM linked. Very good little illustration.

[Clueless Morgan]

@CM,

So are you saying I'm not completely wrong then? I'm not sure whether you quote me to disagree on a specific point or to elaborate further

To elaborate further and to clarify when speciation occurs.  It seemed like you were still unclear about what Mito-Eve meant.

Ok this makes more sense, I didn't consider the "genetic mutation" angle of it, I was thinking more in terms of evolution being too slow to suddenly pump out a new species in one generation.

(I'm going off memory so I'm going to get stuff wrong but here's another example)

There is a family in Northern Italy that has a mutation that makes them very tolerant to high levels of cholesterol, levels that in other people would guarantee that they develop heart disease, clogged arteries and other related health problems, but this family's mutation makes them sort of "immune" to such problems. This mutation has been traced back to a single ancestor, a man who lived in the late 1700s who lived long enough to father children and pass this mutation on such that it has survived to this day in a town in Northern Italy. If this mutation continues to spread throughout the human population such that in 100,000 years every human has this mutation, this man would be considered the most recent common ancestor, the Cholesterol-Resistance-Adam if you will, in the way that Mito-Eve is considered the most recent common ancestor from which everyone can trace their mtDNA.

When we're talking about Mito-Eve and Y-Adam, we're talking only about that one aspect of their genetics that proliferated throughout the species. If you trace back any other specific gene you could theoretically trace it back to its own Adam or Eve, the creature from which that gene mutation originated.