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Is it tautological that all living humans descended from a single male and single female human ancestor?

Is it tautological that all living humans descended from a single male and single female human ancestor?


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Many popular science articles cite high sequence conservation of mitochondrial DNA and the Y chromosome among living people as evidence that all humans are descended from a single male and single female human ancestor.

Is sequence evidence necessary to make this assertion, or does it follow tautologically from the definition of speciation? What would a speciation pedigree look like for a species that does not pass through a single-individual bottleneck?


Human Y-chromosome DNA haplogroup

In human genetics, a human Y-chromosome DNA haplogroup is a haplogroup defined by mutations in the non-recombining portions of DNA from the male-specific Y chromosome (called Y-DNA). Many people within a haplogroup share similar numbers of short tandem repeats (STRs) and types of mutations called single-nucleotide polymorphisms (SNPs). [2]

The human Y-chromosome accumulates roughly two mutations per generation. [3] Y-DNA haplogroups represent major branches of the Y-chromosome phylogenetic tree that share hundreds or even thousands of mutations unique to each haplogroup.

The Y-chromosomal most recent common ancestor (Y-MRCA, informally known as Y-chromosomal Adam) is the most recent common ancestor (MRCA) from whom all currently living humans are descended patrilineally. Y-chromosomal Adam is estimated to have lived roughly 236,000 years ago in Africa. By examining other bottlenecks most Eurasian men (men from populations outside of Africa) are descended from a man who lived in Africa 69,000 years ago(E-M168). [ citation needed ] Other major bottlenecks occurred about 50,000 and 5,000 years ago and subsequently the ancestry of most Eurasian men can be traced back to four ancestors who lived 50,000 years ago, who were descendendant of African (E-M168). [4] [5] [6] [ clarification needed ]


Genetics and Human Evolution

Recent technological breakthroughs in genomic analysis, combined with archeological, paleoanthropological, linguistic and other information, now give us an unparalleled opportunity to trace humanity’s evolution and movement in time – how we developed, differentiated and interbred many times, and arrived at our present planet-wide population.

Until recently, the leading theory of human population descent, known as the “serial founder” model, envisioned modern humans expanding out of Africa and the Near East around 50,000 years ago and leaving descendent populations along their routes of migration. The settlements of these groups were thought to remain unmixed for tens of thousands of years, and consequently were classified according to location, superficial appearance and culture as East Asians, Caucasians, West Africans, Native Americans and Australasians.

We now know, thanks to studies of ancient DNA (aDNA), that the serial founder model is wrong. It turns out that present-day populations are actually mixtures of highly divergent populations that no longer exist. Nor are present-day populations, thanks to perennial migration and mixing, exclusive descendants of the populations that lived in the same locations ten thousand years ago.

Scientific Breakthrough

The announcement of evolutionary trees based on variation in mitochondrial DNA in a 1987 edition of Nature, followed by a study on evolution of the human Y chromosome a few years later, staggered the world. From the pattern created by the random genetic variations on both of these lineages, geneticists can conclude facts rather than suppositions and can of course construct family trees for everyone alive today.

DNA molecules make up the human genome, the genetic code that each of us inherits from our parents. DNA consists of twin chains of molecules called nucleotides made from the chemicals adenine (A), cytosine (C), guanine (G) and thymine (T). Each chain, broken up into 23 chromosomes, adds up to about three billion chemical blocks in length. Genes are fragments of these chains, generally around a thousand nucleotides long, each one telling something about how the body is built.

Each time egg and sperm are created, the approximately 3 billion base pairs of DNA comprising our genes are copied. Random variations in these inherited sequences are called mutations – or markers. They are what make us individual, and they are also the means by which individual ancestry can be determined. Since these changes occur at a known constant rate over time roughly once every thousand nucleotides the greater number of differences between two people’s mutations, the further they are away from sharing a common ancestor.

Mitochondrial DNA (mtDNA) is inherited only through the maternal line in humans. This knowledge enabled geneticists to demonstrate that all humanity descended from a single female ancestor, now known as “Mitochondrial Eve,” and established that her birthplace, and that of all humanity, was Africa.

All male mammals have one Y chromosome that contains a gene called SRY, which triggers the development of a male. The Y chromosome is passed down essentially unchanged from one generation to the next in other words, the Y chromosome DNA of all living men is related through a single male ancestor who lived 60,000–100,000 years ago. This discovery enabled population geneticists to trace human ancestries through the pattern of mutations or markers carried on the male Y chromosome.


Do all living humans share a (human) common ancestor?

The Wikipedia article on the MRCA seems to be quite clear to me, but some folks have told me that I'm misunderstanding the term MRCA, and that living humans do not share an individual common ancestor - that the "common ancestor" refers to a population, or that that ancestor is not human. Can anyone shed some light on this issue, please?

Edit: To be clear, I'm not referring to a "first human" or a population bottleneck, just a single individual from whom we are all descended. A search of the subreddit implies that Mitochondrial Eve should have been one such individual, if not the most recent, but I cannot find any more details on the subject.

This article suggests dates of 120-156 thousand years ago for the common male ancestor, and 99-148 thousand years for the common female ancestor.

It didn't sample every population, but the dates long precede the period of diaspora when modern humans left Africa (meaning that even unsampled populations have a high probability of descent from the same common ancestors), and are an order of magnitude later than the accepted point of modern human origin (so they were definitely humans).

It should be obvious that males and females don't have distinct ancestors in the sense that is being asked here: It's not possible for a single individual to be the sole ancestor of all male humans, and a different individual to be the sole ancestor of all females.

What these definitions mean is that the oldest string of families in which a son had sons is the male common ancestor. If a family has only daughters, then their Y chromosome stops and they're not part of the future male ancestry, but obviously they can still be part of the human ancestry.

The same is conceptually true for "Mitochondrial Eve". Mitochondrial Eve was the oldest individual to whom an unbroken chain of daughters can be traced. A single generation that only had sons would disrupt the chain, but not the family's contribution to human ancestry.

The OP is misunderstanding the concept of a MRCA more specifically, they are misunderstanding the concept of speciation. A new species (usually) does not arise because a single individual develops a show suite of new traits. Usually a whole population drifts gradually away from another population there's no single individual that was the ancestor of an entire new species.

The OP cites Wikipedia as claiming that a single individual is ancestral to all humans. Here's what Wiki actually says:

The MRCA is the most recent common ancestor shared by all individuals in the population under consideration. This MRCA may well have contemporaries who are also ancestral to some but not all of the extant population.

That should help clarify the confusion. My grandfather was the most recent common ancestor of me, my children, and my cousins. Does that mean we all arose entirely from my grandfather, with no contribution from any other individuals? My wife would disagree. We share a common ancestor, but we arose from a population that extended over multiple continents with very different ancestries.


Our ancestors may have mated more than once with mysterious ancient humans

It looked like an ordinary finger bone. But when researchers sequenced its DNA in 2010, they uncovered the existence of a group of ancient humans no one had seen before: the Denisovans. Then came an even bigger surprise. Some modern humans also carry Denisovan DNA, meaning that at some point in the ancient past, Denisovans and modern humans mated and had children. Now, a new study concludes that all that free love had some dark consequences, including male offspring that were likely sterile.

In the absence of much fossil evidence, the best way to study Denisovans is through the genes they left behind in modern humans. So population geneticists Sriram Sankararaman at the University of California (UC), Los Angeles, and David Reich at Harvard University sifted through 257 genomes of present-day people from 120 non-African populations around the world. (Africans, whose ancestors didn’t leave Homo sapiens’s original home, do not have any Denisovan heritage.) They confirmed an earlier finding that among humans living today, people from Papua New Guinea, Australia, and other parts of Oceania have the most Denisovan ancestry, between 3% and 6% of their genomes. This compares with about 2% from Neandertals for all non-African genomes.

Sankararaman and Reich found another hot spot of Denisovan ancestry in an unexpected place: South Asia. “It’s about 10% of what we see in the Oceanians,” Sankararaman explains. That’s quite a small contribution—which allowed it fly under the radar in previous studies—but it’s more than researchers expected to find based on their best models of population mixing. East Asians, in turn, have more Denisovan ancestry than Europeans but less than South Asians, the team reports today in Current Biology.

There are a few potential explanations for how modern humans ended up with Denisovan genes, Reich says. It’s possible that Denisovans and modern humans mated only once, presumably while H. sapiens were on their way to Australia and Papua New Guinea. After that, Denisovan-related modern humans mated with modern humans whose ancestors had never met Denisovans, and different populations ended up with different proportions of the archaic genes. “On the other hand, it’s entirely possible, and I think plausible, that what you’re seeing in India is evidence of mixture of ancient South Asian ancestors with local Denisovans,” that is, an entirely separate mating event than the one that led to Denisovan ancestry in Oceania, Reich says. In fact, he explains, “the data could be consistent with as many as three independent mixture events with Denisovans.”

Although it’s difficult to determine which model is right without more data from both fossils and modern human genomes, “I don’t think it’s that hard to imagine that there were multiple admixture events,” says Joshua Akey, a population geneticist at the University of Washington, Seattle, who was not involved in the study. He led a team that recently identified as many as five mixing events between modern humans and Neandertals.

Another mystery is exactly when H. sapiens hooked up with Denisovans. Fossil evidence from Denisova Cave suggests that the ancient species lived there from as early as 170,000 years ago to at least 50,000 years ago, and who knows when they might have occupied the rest of Asia. That gives Denisovans a lot of time to run into other kinds of humans and potentially have babies with them.

But Sankararaman and Reich knew that with each successive generation, the chains of Denisovan DNA would become shorter and shorter, as the two parents’ genomes broke apart and recombined to form their children’s genomes. So they counted backward, starting from the comparatively long chains of Denisovan DNA in Oceanic populations. They did the same for their Neandertal ancestry, finding that modern humans mixed with Denisovans 5000 to 10,000 years after they mated with Neandertals. Reich and Sakararaman had already estimated that Neandertals and modern humans mated approximately 50,000 years ago, which would put the Denisovan interbreeding event—at least the one that contributed to Oceanic populations—at about 40,000 years ago.

The fact that both mixing events occurred around the same time paints an intriguing picture of what H. sapiens got up to as they spread around the world, says Rasmus Nielsen, a population geneticist at UC Berkeley who wasn’t involved in the study. “It suggests a scenario of extensive, and almost free, matings” between modern humans and just about any other closely related species we met.

But there were consequences to the love fest. Some of them were positive, such as a Denisovan gene inherited by Himalayan populations that reduces hemoglobin levels in the blood, allowing people to thrive at extremely high altitudes. Sankararaman and Reich also found evidence that Papua New Guineans have a Denisovan gene that may help them detect very subtle scents. Still, they also noticed that no trace of Denisovan ancestry remained on modern humans’ X chromosome or on the genes that express themselves in the tissue of the testes. That’s a pattern scientists see in many interspecies hybrids, and it’s a sign that when the two species get together and make babies, their male offspring are infertile. “That’s the barrier that keeps the species from mixing,” Sankararaman explains. Male Denisovan–H.sapiens hybrids, in other words, represented a genetic dead end. The traces of Denisovan ancestry researchers see today had to have been passed down by female hybrids. So, if you have Denisovan ancestry, you can thank your ancient grandmothers.


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Sampling of the human Y chromosome eliminates the curious disparity in ages of our last common male and female ancestors. [Also see Reports by Poznik et al. and Francalacci et al.]


Is it tautological that all living humans descended from a single male and single female human ancestor? - Biology

All modern humans descended from a solitary pair who lived 100,000 to 200,000 years ago, scientists say.

Scientists surveyed the genetic 'bar codes' of five million animals - including humans - from 100,000 different species and deduced that we sprang from a single pair of adults after a catastrophic event almost wiped out the human race.

These bar codes, or snippets of DNA that reside outside the nuclei of living cells, suggest that it's not just people who came from a single pair of beings, but nine out of every 10 animal species, too

Stoeckle and Thaler, the scientists who headed the study, concluded that ninety percent of all animal species alive today come from parents that all began giving birth at roughly the same time, less than 250 thousand years ago - throwing into doubt the patterns of human evolution.

'This conclusion is very surprising,' Thaler admitted, 'and I fought against it as hard as I could.'

The new report from experts at the Rockefeller University along with from the University of Basel published the extraordinary findings in Human Evolution.

The research was led by Senior Research Associate Mark Stoeckle and Research Associate David Thaler of the University of Basel, Switzerland.

They mined 'big data' insights from the world's fast-growing genetic databases and reviewed a large literature in evolutionary theory, including Darwin.

Dr Stoeckle said: 'At a time when humans place so much emphasis on individual and group differences, maybe we should spend more time on the ways in which we resemble one another and the rest of the animal kingdom.'

The conclusions throw up considerable mystery as to why the need for human life to start again was needed such a relatively short time ago, especially since the last known extinction we know of was during the time of the dinosaurs 65 million years ago.

This opens up the possibility of an inbuilt human evolutionary process wherein we break down and die out, leaving the need to start from scratch.

We're also surprisingly similar to not just every other human, but every other species.

'If a Martian landed on Earth and met a flock of pigeons and a crowd of humans, one would not seem more diverse than the other according to the basic measure of mitochondrial DNA,' said Jesse Ausubel, Director of the Program for the Human Environment at The Rockefeller University.

'Culture, life experience and other things can make people very different but in terms of basic biology, we're like the birds,' Dr Stoeckle added.

The 'mitochondrial DNA' examined in the research is that which mothers pass down from generation to generation and it showed the 'absence of human exceptionalism.'

'One might have thought that, due to their high population numbers and wide geographic distribution, humans might have led to greater genetic diversity than other animal species,' added Stoeckle.

'At least for mitochondrial DNA, humans turn out to be low to average in genetic diversity.'

The study has been misunderstood by some religious parties who thought it meant that we all came into being in some seminal Big Bang-typed event 100,000 ago, but this isn't what the findings actually suggest.

What Stoeckle and Thaler's findings point to is that our species has to revamp far more often than we thought, and we do so in unison with all animals.


Sandwalk

It may seem like a ridiculous question to ask whether you are a descendant of Charlemagne, who was crowned Emperor on December 25, 800. If you live in Asia or Africa, or your ancestors are from Asia or Africa, then you are probably not a descendant of Charlemagne.

But if any of your ancestors lived in Europe, especially western Europe, then it's almost certain that Charlemagne is one of your ancestors. No matter where your ancestors are from they probably share a common ancestor with everyone else from that region. What's surprising is that many of those common ancestors lived only 1200 years ago.

I'm talking about big regions here, like most of Europe or Asia, or Africa. There's a remarkable amount of inbreeding among human populations at that scale. It's a good example of how evolution works. It's populations that evolve.

Remember that it's populations that evolve, not individuals. With only a few exceptions, species are subdivided into numerous populations with restricted gene flow between them. The sub divisions range from very large group called races, or subspecies, to progressively smaller populations down to local demes or extended families. In small populations, alleles can become rapidly fixed by random genetic drift but the existence of these populations means that it is much more difficult for these alleles to spread to the rest of the species. What we expect to see under those conditions is races or demes that differ substantially in their allele frequencies.

The explosion in amateur genealogy in recent years has highlighted these kinds of population structures in our own species. More and more people are putting their genealogical research on publicly accessible databases such as ancestry.com and many others. The collective result of these, mostly amateur, investigations is remarkable. It means that every one of us can make a family tree.

Well, perhaps not everyone. There's a huge bias towards Caucasians in the genealogy databases. There are many reasons for this bias but we won't go into them in this post. The important result is that we can all learn something about human populations from this data even if it doesn't include your own ancestors.

The other recent development is the increasing number of people who are having their DNA analyzed and posting the results online. This is much more important since people all over the world are participating and we will soon have a good picture of the genetic structure of today's populations. This complements the family tree data in the same way that gene phylogenies complement the fossil record.

What about Charlemagne? Amateur European genealogists have to do a lot of work to document their ancestors back four or five generations. This takes them to the 1800s (30 years per generation). 1 At that point in time they have 16 or 32 direct ancestors and chances are they'll be able to hook up with others who share these ancestors. The farther back you go on your own, the greater the chances that someone will have researched your ancestor.

The idea that many of us are related to Charlemagne is not new. Here's what they say on the Genealogy of Presidents website.

If you examine the List of United States Presidents by genealogical relationship you'll see that 19 US Presidents are descendants of British royalty and therefore, almost certainly, descendants of Charlemagne. Note that US Presidents are not royalty, they are, to all intents and purposes, ordinary citizens, just like you and me.

It's almost trivial to find connections to the US Presidents if you have ancestors who settled in the British colonies in the 1600s. I'm related to George Bush, for example, through the Shermans of Rhode Island and Connecticut. The good news is that I'm also related to Winston Churchill though the same family.

The amazing thing about genealogy is how closely related everyone is once you start looking. This isn't so amazing to population geneticists.

It's not so hard for North Americans to find European ancestors but many lineages terminate because parish records have not been preserved and because there are no other sources for the ancestors of average citizens. But every now and then you'll stumble upon lineages that have been well researched. Among my own ancestors for example there are half a dozen lineages that reach back to the 1400s and beyond. All I did was find the connections to those lineages.

The history of European nobility is well known. Chances are, you have at least one ancestor who connects to the various Dukes, barons, Counts, and Knights and their spouses in medieval times . A large percentage of the nobility of the European nobility can claim descent from Charlemagne. He had 20 children.

With a little effort, almost everyone of European descent can find the path to Charlemagne. If your ancestors are from England or Scotland your connection often runs through William of Normandy and a bunch of other tourists from France who visited England in 1066. Be careful, though, because there are many incorrect genealogies on the web and you'll need to do some fact checking. I found three different connections to nobility but two of them were figments of someone's overactive imagination. [See My Family and Other Emperors for my relationship to Charelmeange.]

Expert genealogists, as opposed to amateurs, are very frustrated by these errors on the internet. Because of the nature of the databases, it's very hard to remove errors once they start being incorporated into various genealogies.

The fact that all Europeans have several recent common ancestors tells us a lot about the genetic makeup of this population. It is quite homogeneous and there's a lot of inbreeding. It seems to be extremely rare to discover a non-European ancestor once one goes back a few hundred years. (It's much more common in recent times.) I presume this lack of outbreeding also applies to Asians, Africans, and all other groups.

Given that the average generation is 30 years 2 , if you go back to 800 that's about 40 generations. Potentially you have 2 40 ancestors. That's more than 1 trillion ancestors alive in 800. I don't know what the population of Europe was in 800 but I strongly suspect it wasn't even close to one trillion people. I suspect it was only about 25 million. It's not surprising that you are related to many of them.

It would be interesting to know how many people who were alive in 800 have direct descendants who are alive today. Maybe there's a way of calculating this?

1. In my case it was my mother who did/does all the work. I just surfed the internet using her data.

2. The actual calculated value for my ancestors is 29 years per generation.


DNA: Comparing Humans and Chimps

These three species look alike in many ways, both in body and behavior. But for a clear understanding of how closely they are related, scientists compare their DNA, an essential molecule that's the instruction manual for building each species. Humans and chimps share a surprising 98.8 percent of their DNA. How can we be so similar--and yet so different?

So Much Alike.

Human and chimp DNA is so similar because the two species are so closely related. Humans, chimps and bonobos descended from a single ancestor species that lived six or seven million years ago. As humans and chimps gradually evolved from a common ancestor, their DNA, passed from generation to generation, changed too. In fact, many of these DNA changes led to differences between human and chimp appearance and behavior.

Examine the Evidence

Matching DNA? Human and chimp DNA is nearly identical when you compare the bands on chromosomes, the bundles of DNA inside nearly every cell. Which two chromosomes are more alike?

Banding Patterns

The light and dark bands on these chromosomes, created by a laboratory dye, reveal similarities and differences among human, chimp and mouse DNA.

Human and chimp X chromosomes both contain about 1,100 different genes, or sets of instructions. Each gene affects a particular trait in the body.

HEM B - Blood clotting, hemophilia
CPX - facial development, cleft palate
SMC1L1 - chromosome maintenance
OPN1LW - red color vision

Seeing Red

Most genes in humans and chimps are nearly identical. Both species have the OPN1LW gene, which allows them both to see the color red. But mice lack OPN1LW--and have trouble seeing red.

. And Yet So Different

If human and chimp DNA is 98.8 percent the same, why are we so different? Numbers tell part of the story. Each human cell contains roughly three billion base pairs, or bits of information. Just 1.2 percent of that equals about 35 million differences. Some of these have a big impact, others don't. And even two identical stretches of DNA can work differently--they can be "turned on" in different amounts, in different places or at different times.

Same Genes, Behaving Differently

Although humans and chimps have many identical genes, they often use them in different ways. A gene's activity, or expression, can be turned up or down like the volume on a radio. So the same gene can be turned up high in humans, but very low in chimps.

The same genes are expressed in the same brain regions in human, chimp and gorilla, but in different amounts. Thousands of differences like these affect brain development and function, and help explain why the human brain is larger and smarter.

Slightly Different Genes

The chimpanzee immune system is surprisingly similar to ours--most viruses that cause diseases like AIDS and hepatitis can infect chimpanzees too. But chimps don't get infected by the malaria parasite Plasmodium falciparum, which a mosquito can transmit through its bite into human blood. A small DNA difference makes human red blood cells vulnerable to this parasite, while chimp blood cells are resistant.


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

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]

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:

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

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



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