Adam and Eve
March 10, 2011 9:15 PM   Subscribe

Please point me to scientific resources/articles either in support of or refuting the "biblical" claim that all humans are descendants of a single pair of male and female (i.e. Adam and Eve)

I've always had the vague notion that we couldn't have all come from a single pair of human ancestors because of genetic variation and such, but recently I heard a friend's claim that mitochondrial DNA evidence supports the claim that we all descended from a single female ancestor. I read the wiki article on Mitochondrial Eve I'm not really sure how "conclusive" mitochondrial DNA evidence is. So I would like to do some further reading, and would appreciate any insights/resources you can point me toward. Thanks!
posted by oracle bone to Science & Nature (16 answers total) 3 users marked this as a favorite
I don't know whole lot about genetics, but I can link you to this article by evolutionary biologist Jerry Coyne. Choice quote:

"Mitochondrial “Eve” was the ancestor of only our mitochondrial DNA. It’s extremely improbable (I’d say the chances are zero) of any other gene not in the mitochondrial DNA descending from this same woman. "

Basically, mitochondria are one tiny organelle that got subsumed into our cells a long time ago. To claim that mitochondrial DNA proves we are all descended from one woman is at best ignorant, and at worst dishonest.
posted by lholladay at 9:22 PM on March 10, 2011

Doesn't any material on the phenomenon of inbreeding fit the bill? Minimum viable population at Wikipedia.

Unless God was personally reaching in and randomizing the DNA in everyone's gonads for the first few centuries. It would be cool to start a splinter sect based on that, let's do it.

But anyways, I don't think that the "Mitochondrial Eve" thing actually means that the entire population of humans was made up of two individual organisms at any point, just that we can pinpoint at least one common ancestor. I'm not a scientist so I'm basically pulling this out of my ass but I would think that there were other humans alive at that point, just not ones that we're all descended from.
posted by XMLicious at 9:35 PM on March 10, 2011

Keep in mind that the "Eve" in the Mitochondrial Eve scenario isn't a specific woman, and that no aspect of that hypothesis speculates that such a woman literally was the first female Homo Sapiens mating with the first male Homo Sapiens to produce all further human beings.

It's really just an expression, is my point.
posted by Sara C. at 9:40 PM on March 10, 2011 [1 favorite]

First, a small correction. If one reads the biblical account of Noah, then there are actually five seed-stock humans: Noah, his wife, and the wives of his three sons. (The sons themselves, of course, get all their genes from their parents, so they don't have any unique genetic material.)

But among them only one is male, and if we were all descended from those five, then every man alive would have virtually the same Y chromosome. A few thousand years, a couple of hundred generations, isn't long enough to create the kind of variety among Y chromosomes which has been experimentally found by gene sequencing unless you posit a mutation rate VASTLY greater than any evolutionist would dare to postulate.
posted by Chocolate Pickle at 9:40 PM on March 10, 2011 [3 favorites]

...mitochondrial DNA evidence supports the claim that we all descended from a single female ancestor.

What that claim means is that there is a single woman back there from which we are all descended. It doesn't mean that we are not also descended from other women who lived at the same time.
posted by Chocolate Pickle at 9:42 PM on March 10, 2011 [2 favorites]

Oh, crap. Somehow I got it in my mind that you were talking about the Noah story. Anyway, the argument about the Y chromosome also works if you're talking about Adam and Eve.
posted by Chocolate Pickle at 9:49 PM on March 10, 2011

Mitochondrial Eve is a very special woman. She is not our most recent common ancestor. She's not the "first human". She's not the only common ancestor of humanity from that time. She is the most recent common ancestor through strictly female lines.

It is close to certain that there is a more recent common ancestor of all humanity. It is a sure thing that there were other people alive at that time who were ancestors of every living human.

In other words - no, this does not prove that there was an original Adam and Eve. Not even close.
posted by It's Never Lurgi at 9:58 PM on March 10, 2011

Keep in mind that the "Eve" in the Mitochondrial Eve scenario isn't a specific woman...

She was, in fact, an individual. One "specific woman". What else could she be?

If fact, all of us here on this planet, plants, animals, protozoa, and germs, share a single common ancestor; an ancestor that was a specific, individual organism. It's called LUCA.
posted by mr_roboto at 10:48 PM on March 10, 2011

Keep in mind that the "Eve" in the Mitochondrial Eve scenario isn't a specific woman...

She was, in fact, an individual. One "specific woman". What else could she be?

Both of you are right. The important thing to recognize here is that while Mitochondrial Eve is a specific woman right now, she's not necessarily going to be the same woman 50,000 years from now. It's like saying "The President of the United States isn't one specific person" -- currently it's Barack Obama, but that's just the current state we're in. If a specific subset of the population were to die off today, Mitochondrial Eve could be a new, different, specific woman (who lived a long time ago).

To make a really crappy analogy, all of the CPUs in my apartment are most-recently-descended from the transistor created in Bell Laboratories (not the vacuum tube, because I don't have any tube amps). If I were to remove the Apple devices, all the computers in my apartment would be descended from the Intel 80826 chip.
posted by 0xFCAF at 12:49 AM on March 11, 2011 [3 favorites]

Mitochondrial DNA is passed on from a mother to her children, not from their father, unlike nuclear DNA which is inherited from both parents. So it works like last names, only passed down on the female line instead of the male line. If my last name is Thomson, I owe that to an a series of male ancestors who had sons and passed on that name. However, I'm still descended from all of my other ancestors and have some of their DNA.

Mitochondrial Eve is a woman all people are descended from on a unbroken female line, but not the only female human ancestor. It works out this way because all people have mothers, but not all women who have children have daughters.
posted by nangar at 3:36 AM on March 11, 2011

Best answer: The first line of refutation comes from a population genetics perspective of there not being enough genetic diversity in the population. This is true mainly because of the forces of genetic drift. When the population size is small random a sampling of mates (although with all the begetting one could argue it was indeed not random and the variation in the paternal generation was perfect so as to account for this...) results in an exclusion of particular alleles.

In small populations that we are trying to conserve this is often a major difficulty because due to errors introduced by sampling certain alleles that are recessive and deleterious have a much higher chance of becoming fixed in the population when in a larger population they exist at a basal rate and aren't much of a problem. When they become fixed they are difficult to get rid of as the mutation rate is incredibly low and on average would take many generations to replace the deleterious allele let alone with one that has a higher fitness. This problem is compounded by the fact it doesn't just occur at one loci but multiple! Suddenly the entire population has low birth rates and the ones that do survive are crappy. Slight tangent.

To summarize that portion the process of genetic drift would make the population inviable over a long period of time and if that were the case we would have had a severe founder effect resulting in not many copies of the same gene (oh! you can use the word allele and gene interchangeably more or less) and thus we'd all have a bunch of copies of the same which in every other species is bad. As another poster mentioned: inbreeding depression.

The second approach would be to look at the theorized phylogenies of humans. There have been a couple studies that show hybridization events between early humans and Neanderthals/Denisovans (with autosomal evidence not just mtDNA) which may or may not fit into to your origination scheme, primarily because defining speciation to a very precise level is hard especially in the very contrived scenario of us being the product of a single pair mating (it just didn't happen). On a broader phylogenetic level one may argue that an earlier population served as the human progenitor and then a male and female were isolated and gave rise to humans as we know it. This is still false for the other reasons I've mentioned, but also because it doesn't establish the clear lineage that we know is necessary.

On second reading I ranted to see you wanted some sources so...
This article is a good summary of human phylogeny that establish the groundwork of what we know now it terms of human relations [WARNING PDF LINKS BELOW]:

Worldwide Human Relationships Inferred from Genome-Wide Patterns of Variation Jun Z. Li et al. (2008)

This has a quick summary and I probably could have linked this and been done, but I only gave this paper a cursory read:
The Myth of Eve: Molecular Biology and Human Origins

This is on Denisovans and a really really cool paper:
Genetic history of an archaic hominin group from Denisova Cave in Siberia. Reich et al. (2010)

These papers directly contended the population couldn't have been small (one is no more than sub 50 the other is 10,000. One is also in the reference in the wiki article you mentioned same author for both:

Allelic Genealogy and Human Evolution. Takahata. (1993)

A simple genealogical structure of strongly balanced allelic linesand trans-species evolution of polymorphism. Takahata. (1990)

The references on these are all a good starting point too. Also not going to proofread, I'm sleepy, forgive me =D
posted by EsotericAlgorithm at 3:54 AM on March 11, 2011

Graph theory! Yay!
Remember that "family tree" is a misnomer. It would work if reproduction was asexual, but it's not. Think about how many grandparents you have, then great grandparents, etc. Go back a few thousand years and the chances are pretty good that any two people share lots of ancestors.
posted by monkeymadness at 4:33 AM on March 11, 2011

Mitochondrial Eve was an individual woman, but she may have live centuries before the genetic bottleneck that resulted in her mitochondrial DNA being the single source for all of our current mitochondrial DNA.

This is distinctly different from the concept of Adam and Eve. The biblical account implies that one pair of individuals gave rise to all of humanity, and that no individuals preceded this couple. The data related to Mitochondrial Eve do not support this view. Rather, the general idea is that plenty of genetically distinct individuals existed hundreds of thousands of years ago but, by chance and chance alone, one individual's mitochondrial DNA was the surviving DNA during an unfortunate bottleneck in our evolutionary history. This does not preclude humans living alongside and before mitochondrial Eve, and therefore does not support the Adam and Eve story.

By very poor analogy: Imagine that there is a nuclear holocaust tomorrow, and that all of the women in the world become barren save one. And that this one fertile woman then goes on to produce children that repopulate the world. Two hundred thousand years from now, all women (and men, for that matter, since me inherit their mothers mitochondrial DNA) will share the same mitochondrial DNA as that one fertile woman. But that does not mean that the lone surviving fertile woman was the first woman on earth. She was merely the one whose DNA happened to survive to the current era.
posted by kisch mokusch at 5:06 AM on March 11, 2011 [2 favorites]

I'm not really sure how "conclusive" mitochondrial DNA evidence is.

It isn't a matter of conclusive evidence. It's a purely logical argument. All humans are the same species. Therefore all humans have a common ancestor. That's it.

You can refine it further by asking for other constraints. The most recent *female* ancestor. The most recent female ancestor *that shares particular genes*. The most recent female ancestor that shares particular genes *specifically those found in mitochondria*.

Mathematically or logically speaking, this person has to exist just by the definition of how ancestry works.

The evidence comes in when you ask when she lived or what she might have looked like or other factual questions.
posted by DU at 5:16 AM on March 11, 2011

Chocolate Pickle, I don't think it really helps to point to the Noah story to say there were 5 rather than 2 "seed stock" humans. All five would be descendants of Adam and Eve in a literalist reading. If I start with two hamsters, breed a population of thousands all descended from those two, and then drown all of them except five from the same family, I don't think it makes since to say that their descendants will be more genetically diverse than the population that would have existed if I hadn't committed a near-complete hamster genocide.
posted by Pater Aletheias at 9:37 AM on March 11, 2011

The evidence comes in when you ask when she lived or what she might have looked like or other factual questions.

Okay.... When did Eve live? What might she have looked like?
posted by exphysicist345 at 6:22 PM on March 11, 2011

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