Y and mtDNA are not Adam and Eve: Part 2 - What it means to be the Most Recent Common Ancestor?

| 65 Comments

Part 1 is here.

There were more than two.
One of the misleading aspects of the “Adam and Eve” analogy, is the implication that there were only two humans alive at that time. In the video below I explain what the mtDNA is, how it can be used to trace back to find a common mtDNA ancestor, and why this genetic female was not alone. The same logic applies to the Y chromosome ancestor. Scientists estimate there were approximately 5,000 genetic females and 5,000 genetic males in the ancestral population of anatomically modern humans.

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Talking with people and making this video brought up a couple other important points that are difficult to summarize in a sentence, so I’ll expand upon later:

1. One person (or two people) did not have the ancestral state of all of our DNA.
The person whose cells housed the common mtDNA ancestor (or Y ancestor) also had all of the other chromosomes (1-22 and X), but did not house the common ancestor of each of these chromosomes. These non-sex chromosomes are a lot more complicated. This touches on why it is also misleading to refer to the common ancestor of genetic “males” versus “females.” Genetic females are not only their mtDNA - we also have 22 non-sex chromosomes, and two X chromosomes! Genetic males are not only their Y (and mtDNA), they also have 22 non-sex chromosomes and one X chromosome! Because the non-sex chromosomes (autosomes) can swap DNA, and are inherited through both the sperm and the egg, they much more complicated history than the Y and mtDNA.

2. A lower bound, not a point estimate.
Tracing back to the common ancestral mtDNA or the common ancestral Y chromosome does not tell us when anatomically modern humans arose. We can estimate the TMRCA, or the Time to the Most Recent Common Ancestor, but this mtDNA surely existed much further back in time.

Consider this:



If you didn’t watch the movie, I’ll remind you that in this example, you and your sister are my genetic cousins, and our moms are sisters. In the above example you can see how we can trace all modern mtDNA back to a common mtDNA ancestor (the dotted lines indicate more than one connection is not shown).

Now imagine that a horrible disaster killed off everyone except for our family:


Then, the Most Recent Common Ancestor of all mtDNA really is just our grandma. The previous mtDNA ancestor still existed, but she is no longer the MOST recent.

There is so much to talk about here! My list keeps getting longer.

Coming soon:

  • What I do understand about the paper, and how it fits with recent Y discoveries.
  • What I don’t (yet) understand about the results.
  • You’ll say I’m being to harsh, but I do want to discuss why the title is also misleading to people (separate sexes existed waaaay before humans, and waaaay before genetic sex determination).
  • And, for fun (and a friend) - How fast would evolution have to be if all of modern humans really did descend from only two people - with LOTS of assumptions.

65 Comments

Dear Melissa,

I liked most of your post but disagreed with some points and figured it couldn’t hurt to drop you a line with my perspective.

We reference the popular nicknames for the MRCAs in a single sentence that is heavily laden with qualifiers: “popularly referred to as” and “the so-called,” and I disagree that an 1800-word distillation of a 50-page manuscript would have been the proper forum to discuss this pre-existing analogy and its limitations in further depth (your second proposal). As I see it, this is the role of the press release, which was written by the Stanford Office of Communication and Public Affairs with our help. At our insistence, it clarifies the limitations of the A/E analogy in the introduction. After explaining each of the points you have addressed in your post to every journalist with whom I spoke, I forwarded this press release.

The alternative, your first proposal, was not to reference the MRCA nicknames at all. I do not believe omission on our part would have precluded their usage (and misusage) by the media. The monikers are pervasive in the popular literature on this subject, and to ignore them completely would have been odd. Clearly, the A/E analogy falls short on many fronts. Similarly, the “Methuselah” mutation in IGF1R does not confer millennial longevity, nor does the death of a carrier presage a Great Flood. No cloak and scythe are involved in “Grim / Reaper”-triggered apoptosis, and the LOF mutation to “Sonic Hedgehog” does not confer extraordinary speed. Likewise, there are numerous ways in which the mechanism underlying general relativity is unlike a bowling ball on a rubber sheet. One could protest that it is “misleading” to represent the space-time continuum with a physical medium, but the rich imagery is a fantastic starting point for an exposition. Analogies are by their nature imperfect.

Personally, I am not a big fan of the A/E analogy in particular, but we did not “supply” it. For better or worse, it has been in usage for over 25 years. See, for example, “Estimating the age of the common ancestor of men from the ZFY intron” (Donnelly, Tavaré, Balding, and Griffiths, Science, 1996). In this classic one-page paper, some of the greatest minds in coalescent theory use “Adam” without qualification four times, because the analogy and its limitations were already well-understood to readers of the journal at the time of writing. Please also note their usage of “common ancestor of men” in the title. Of course, one would prefer the term “most recent” to be included, but the 96-character limit does not allow for this, and it is unclear to me how one makes the jump from “common ancestor” to “origin.”

The analogy for a common maternal ancestor has generated great public interest and involvement in genetic ancestry forums, and it is encouraging to see non-scientists meaningfully engage with the science. Even though they have their limitations, we respect that these terms have become pervasive in popular science. For example, Bryan Sykes, a genetics professor at Oxford, has written two very popular books, “The Seven Daughters of Eve” and “Adam’s Curse.” When communicating with science journalists, we did our best to stress the accurate aspects of the analogy and correct the inaccurate ones.

With clear qualification, followed by a press release that explicitly deconstructed it, we referred to the existence of an analogy that has been in use for a quarter of a century. I disagree that this constitutes “misrepresentation” of our work.

No hard feelings or anything; I just wanted to share my thoughts. I am looking forward to your analysis of the paper, and I’d be happy to discuss if you are interested.

Sincerely, David Poznik and Brenna Henn

Hi David and Brenna,

Thank you for your thoughtful response. Really, I do appreciate that you both took the time to write out your thoughts.

I agree that omitting the reference likely would not have prevented several in the the media from latching on to the A&E analogy, but it may have. There have been several other papers looking at TMRCA on the Y (recently Mendez et al 2013 AJHG) that did not reference Y Adam, and still had a lot of press coverage. By including it, you and your collaborators gave permission to use it, regardless of the press release (which three journalists have now told me they were confused by). I am in favor of simplifying our language, and giving accessible analogies, but in this particular case, I do think that the A&E analogy is not only burdened with cultural baggage, but it really is not a good analogy, as I am laying out in my series of posts.

I have been a part of several discussions, with scientists, laypeople and journalists suggesting that the “Adam and Eve” references are, in fact, quite misleading, specifically for some of the reasons I first discussed. To my surprise (and dismay) new misunderstandings that I did not anticipate, related to the analogy, keep arising! You are very welcome to comment on the post, or read through the comments here, to get a sense of what some misconceptions are.

You are quite correct that you are not the first, nor the last, to reference mtDNA Eve or Y chromosome Adam. I did state this in the post. If I am ever asked to comment on a paper with these analogies, I will continue to voice my concern that they are inaccurate representations and lead to misunderstandings among the public. And, if I am ever cited in a news article that throws around A&E without explaining it, I will, as I did in this case, write a response.

No, we do not disagree on this aspect; an 1800 word distillation of a 50 page paper is not the place to get into a discussion of the pre-existing analogy. We do, however, disagree on whether it was worth mentioning it the first place. I think the fact that a poor analogy has been used before is no justification for perpetuating it. People in the scientific community may be aware of it, but for many in the general public, this, honestly, is one of the first times they’ve heard of it. A single sentence can in no way convey the complex history behind these analogies, and mentioning them only gives them more life.

The “misrepresentation” is that the A&E analogy is simply a poor analogy for MRCAs because, among other things, it conflates a genomic region with an entire individual. It is not, in any way, a reflection on your research.

I would very much like to get your opinion on my write up of the research described in your paper! We’ll stay in touch.

Thank you again for your letter.

Sincerely, Melissa

Fascinating blogs, Melissa! Thanks. Some of it is a bit beyond my grasp considering it’s been a decade since I took intro biology in university, but the video is a nice supplement. Looking forward to your other upcoming segments.

Tenncrain said:

Fascinating blogs, Melissa! Thanks. Some of it is a bit beyond my grasp considering it’s been a decade since I took intro biology in university, but the video is a nice supplement. Looking forward to your other upcoming segments.

Thank you! Please let me know what questions you still have, and I’ll try to address them in later posts.

Very refreshing perspective. Did mtDNA Eve share the fruit basket with her contemporaries? Or is that a question best answered by Stephen Meyers?

Melissa:

You said:

“Now imagine that a horrible disaster killed off everyone except for our family:”

Do you think a worldwide flood could have been such a disaster?

Maybe the problem with calling these Y and mtDNA ancestors Adam and Eve is that they really should be called Noah and “the common female ancestor to the wives of Shem, Ham and Japheth.”

See point 1 above, fittest meme. The answer is “no”. If the bottleneck population was 10,000 or so, MRCA could have lived before that.

As expected, Ken Ham finds a way to abuse a metaphor that uses Adam and Eve.

This is similar to the decades of headaches for physicists and chemists caused by the conflation of entropy with “disorder.” Once these memes start propagating, they quickly morph into grotesque misconceptions.

I am so not going there. It’s like those old fried-egg spots. This is your mind on creationism.

Melissa, thanks for your reply. I’m glad we both had the opportunity to express our positions. There’s just one point I wanted to follow-up on.

M. Wilson Sayres said:

… regardless of the press release (which three journalists have now told me they were confused by).

I was surprised by this claim, as I think the Standford press release was crystal clear on the points you’ve addressed in your blog post and on other shortcomings of the analogy. Perhaps there was another press release that we have not seen. I’ll quote a few lines from the Stanford release:

First phrase of the first sentence: Mitochondrial Eve and Y-chromosomal Adam — two individuals who passed down a portion of their genomes to the vast expanse of humanity…

Sentences 9-11: Despite the Adam and Eve monikers, which evoke a single couple whose children peopled the world, it is extremely unlikely that the male and female MRCAs were exact contemporaries. And they weren’t the only man and woman alive at the time, or the only people to have present-day descendants. These two individuals simply had the good fortune of successfully passing on specific portions of their DNA — from the man, the Y chromosome; from the woman, the mitochondrial genome — through the millennia to most of us, while the corresponding sequences of others have largely died out due to natural selection or a random process called genetic drift.

Concluding Paragraph: It’s difficult to say what the apparent overlap between the male and female MRCA sequences may represent, if anything. The vagaries of inheritance are easy to see even within individual human families, and the timing could simply be a fluke. But it’s also possible that it represents a time when only a few sequences were passed on and many died out due to an external event that’s not yet been identified. “For the most part, it’s a random process,” said Poznik. “Some lineages die out, some are successful. But it’s also possible that there may be elements of human demographic history that predispose these lineages to coalesce at certain times.”

Best, David

I am confused by this sentence.

The person whose cells housed the common mtDNA ancestor (or Y ancestor) also had all of the other chromosomes (1-22 and X), but did not house the common ancestor of each of these chromosomes.

I understand it for the Y ancestor (and it may be true for Homo Sapiens), but why does the MRCA for a mtDNA ancestor need to be of the same species as opposed to a precursor?

In your example under point 2 above, what inhibits the common mtDNA ancestor from being so far back that it isn’t the same species? On the other end, the population wipeout scenario makes it pretty clear that the common mtDNA (or Y) may be many (perhaps thousands) of generations after the first of the species appeared.

Thanks Melissa, that was really helpful. Please continue with the rest of the series. I’d like to thank Dr. Poznik for his clarification as well. But I have to disagree with his assessment and say that the A&E analogy can be more damaging than most of the other bad scientific analogies that he listed. As Melissa said, this specific analogy evokes a meaning that is in total contradiction with our understanding of human evolution, and it’s actively used by evolution deniers to throw doubt on the validity of evolutionary theory. And I’m sure that you’re aware of the magnitude of the educational challenge that we face here in this country and in many others when it comes to elucidating the concepts of evolutionary biology. The quote-mining machines of the creationist movement would love to see such bad analogies persist in the scientific literature (as evidenced by the link that Mike has pointed to). This sad reality should make us more cautious in how we formulate and present our ideas.

David, for example - “Nice blog post! I shd say the press release made me think they’d found when 2 genders first arose, which was rly confusing” — Francie Diep (@franciediep) August 6, 2013

MememicBottleneck - There’s nothing, specifically, prohibiting the mtDNA nor the Y chromosome from being from a different species. What I was trying to illustrate here (I’m thinking of doing another video) is that it wasn’t the entire genome of the individuals that was passed on to the present day (for example, all of their non-sex chromosomes and the Y chromosome), it is only the Y chromosome, and perhaps (but not necessarily) parts of their non-sex chromosomes.

Rhazes - Thank you! Will do! I think there might be one more “background” post before I get to the paper.

fittest meme said:

Melissa said:

“Now imagine that a horrible disaster killed off everyone except for our family:”

Do you think a worldwide flood could have been such a disaster?

Maybe the problem with calling these Y and mtDNA ancestors Adam and Eve is that they really should be called Noah and “the common female ancestor to the wives of Shem, Ham and Japheth.”

Except that Y and mtDNA ancestral “Adam and Eve” are not Jewish, date waaaaaaaaaaaaaaaaaaaaaaay beyond 4,000 years ago, and do not imply a bottleneck of 8 individuals.

fnxtr - Your “no” answer to my first question sounds a little defensive. Couldn’t a flood have been what Melissa proposed as “the horrible disaster that killed off everyone but our family?” Even if the bottleneck was 10,000 couldn’t it have been a flood that caused it? If all humans alive today can be linked back to one male ancestor and one female ancestor, whatever the size of the bottleneck, only those directly descended from these ancestors would pass through. So I suppose that the bottleneck “could” be 10,000 individuals but the larger this number gets the more unlikely it becomes that every individual fits the criteria mentioned above.

apokryltaros - OK. I’ll ignore the first statement. How do you know it was more than 4000 years ago? Your right to note that the data doesn’t specifically imply 8 individuals but it certainly doesn’t eliminate the possibility. As I mentioned above it is more probable that the bottleneck is small than large in order to eliminate all humans who were not related to the common Y and mtDNA ancestor.

I’m looking forward to an informed answer from Melissa.

Has anyone actually taken the time to determine “how many people have which misconceptions”?

Here are my thoughts, but I’d appreciate any others:

As I mentioned on the other thread, when I first read about “mtEve” 25 years ago I too had some major misconceptions, but I was not an evolution-denier, much less a Genesis literalist. In fact I’m, still confused on some details.

As far as I can tell from reading many polls, probably no more than 25% of adult Americans are convinced that there were only 2 humans ~6-10K years ago, and that neither had ancestors. Another 15-20% that also chooses the hopelessly ambiguous “humans were created in their present form in the last 10,000” years in the most frequently cited poll are probably “thinking souls, not cells,” and just don’t give it 5 minutes’ thought. The former will not be persuaded by any arguments here because they are either hopelessly compartmentalized, or in a few cases, “in on the scam.” The other 15-20% can be helped, but they are far from the only ones with misconceptions, according to my own (unscientific) poll:

In 25 years of talking to many people, most who understand some science and have no problem with evolution, not one could define mtEve, or give an order-of-magnitude estimate of when she existed (much less that her identity changes), and most had not even heard of the term.

fittest meme said:

apokryltaros - OK. I’ll ignore the first statement. How do you know it was more than 4000 years ago?

Historically speaking, there is plenty of evidence that there was no catastrophe of any kind that created a bottleneck among humans 4,000 years ago, what with, among other things, the Pyramids of Giza being under construction at the time. I mean, I pray to God that you aren’t among those Idiots for Jesus who would say “Yes, one of the very first things Noah did after getting off the Ark and sobering up was to rush from Ararat to Egypt and single-handedly build the Pyramids for the Egyptians (and all other 4,000 year old artificial structures for everyone else) with help from his 3 sons 4,000 years ago.”

Your right to note that the data doesn’t specifically imply 8 individuals but it certainly doesn’t eliminate the possibility. As I mentioned above it is more probable that the bottleneck is small than large in order to eliminate all humans who were not related to the common Y and mtDNA ancestor.

If you understood genetics and biology, you would realize that a bottleneck of 8 individuals would leave very visible signs of inbreeding (either physical, genetic, or both) among their descendants for a very long time, as seen in extremely inbred lineages like European royal families, cheetahs, pedigree dogs, and northern elephant seals.

http://en.wikipedia.org/wiki/Popula[…]eneck#Humans

Humans had a bottleneck event 140 to 70,000 years ago, possibly caused by climatic changes due to the Lake Toba supervolcano volcanic eruption, or due to an extended limited migration out of Subsaharan Africa, limiting the human population to 2 to 15,000 individuals.

If humans really were descended from Noah and his 3 sons, among other things, humans would be far more inbred, and would experience very few, and very poor reproductive successes today (especially if we were descended from 8 individuals 4,000 years ago).

That, and many species have been observed to require a minimum number of individuals to survive a bottleneck event in the first place, what with many species, such as the Passenger Pigeon, going extinct after their population was brought to a level where the individuals simply failed to thrive and reproduce.

Dr. Sayres: I think this recent cartoon from The Reason Stick is relevant to this posting. Mitochondrial Eve

apokryltaros said:

fittest meme said:

apokryltaros - OK. I’ll ignore the first statement. How do you know it was more than 4000 years ago?

Historically speaking, there is plenty of evidence that there was no catastrophe of any kind that created a bottleneck among humans 4,000 years ago, what with, among other things, the Pyramids of Giza being under construction at the time. I mean, I pray to God that you aren’t among those Idiots for Jesus who would say “Yes, one of the very first things Noah did after getting off the Ark and sobering up was to rush from Ararat to Egypt and single-handedly build the Pyramids for the Egyptians (and all other 4,000 year old artificial structures for everyone else) with help from his 3 sons 4,000 years ago.”

Your right to note that the data doesn’t specifically imply 8 individuals but it certainly doesn’t eliminate the possibility. As I mentioned above it is more probable that the bottleneck is small than large in order to eliminate all humans who were not related to the common Y and mtDNA ancestor.

If you understood genetics and biology, you would realize that a bottleneck of 8 individuals would leave very visible signs of inbreeding (either physical, genetic, or both) among their descendants for a very long time, as seen in extremely inbred lineages like European royal families, cheetahs, pedigree dogs, and northern elephant seals.

http://en.wikipedia.org/wiki/Popula[…]eneck#Humans

Humans had a bottleneck event 140 to 70,000 years ago, possibly caused by climatic changes due to the Lake Toba supervolcano volcanic eruption, or due to an extended limited migration out of Subsaharan Africa, limiting the human population to 2 to 15,000 individuals.

If humans really were descended from Noah and his 3 sons, among other things, humans would be far more inbred, and would experience very few, and very poor reproductive successes today (especially if we were descended from 8 individuals 4,000 years ago).

That, and many species have been observed to require a minimum number of individuals to survive a bottleneck event in the first place, what with many species, such as the Passenger Pigeon, going extinct after their population was brought to a level where the individuals simply failed to thrive and reproduce.

But the problem with Floodists is that anything that looks like solid proof that there was no Flood is just some miraculous fix by God that makes it LOOK like there was no Flood. Of course that means that God is being intentionally deceptive in the fake evidence he leaves in the physical world, but they seem perfectly happy with a lying God – starting with that lie about dying on the day you eat the fruit.

Just Bob Wrote:

But the problem with Floodists is that anything that looks like solid proof that there was no Flood is just some miraculous fix by God that makes it LOOK like there was no Flood.

“Floodists” is an interesting word, but I’m not sure which “kind” you mean. The anti-evolution activists appear to be aware that they’re playing a “heads I will, tails you lose” game. As you might know, some activists, most notably the IDers, do not even take the flood literally, but are “pseudoskeptics,” meaning that they claim to have “no dog in the fight” but root against one “dog” while merely ignoring the other. These total less than 1% of adult Americans.

Committed rank-and-file literalists - OECs and YECs - will either filter all evidence through Morton’s Demon or admit that scripture overrules any evidence. That’s the other ~25% that I mention above, along with noting that many more people think a global flood “could be true.” That just gave me a flashback to when I was one of the latter, who just hadn’t thought it through. In 1968 a hit song called “The Unicorn” had lyrics that claimed that unicorns went extinct because of Noah’s flood. I was only 13, but already a strict old-earther who had recently found evolution and common descent convincing. I was even questioning the existence of God. But I had not yet thought of questioning the global flood or the existence of unicorns.

apokryltaros said:

Historically speaking, there is plenty of evidence that there was no catastrophe of any kind that created a bottleneck among humans 4,000 years ago, what with, among other things, the Pyramids of Giza being under construction at the time.

I’m sure you do understand the lack of specificity involved with both contextual and Carbon 14 dating (how does one know that the charcoal pieces used to date the pyramids were not thousand of years old when they were used as fill?). And therefor you also understand why there is controversy among many archeologists and Egyptologists regarding the age of the pyramids.

Regardless of this accuracy the pyramids are dated fairly close to the 4000 year ago date. If this is what you are counting on as your best evidence to support your statement that the bottleneck event happened “waaaaaaaaaaaaaaaaaaaaaaay beyond 4,000 years ago” I’m not impressed.

If you understood genetics and biology, you would realize that a bottleneck of 8 individuals would leave very visible signs of inbreeding (either physical, genetic, or both) among their descendants …

If humans really were descended from Noah and his 3 sons, among other things, humans would be far more inbred, and would experience very few, and very poor reproductive successes today (especially if we were descended from 8 individuals 4,000 years ago).

There is Biblical evidence that you are right about this. Indeed the life spans of individuals were recorded to be much shorter after the flood than they were before. The effect would probably be even more problematic today since the human genome has acquired and passed on a great deal more mistakes (mutations) through many generations of copying. It is these mutations which are the reason inbreeding is a problem.

fittest meme said:

…you also understand why there is controversy among many archeologists and Egyptologists regarding the age of the pyramids.

Name them. Link to scientific discussions (not theological ones) of this alleged controversy.

There is Biblical evidence…

There is no “Biblical evidence.” To cite the Bible has no more evidential value than to cite Harry Potter, or the Greek myths. They are all fiction, not fact.

fittest meme said:

…the human genome has acquired and passed on a great deal more mistakes (mutations) through many generations of copying. It is these mutations which are the reason inbreeding is a problem.

I think you’re incorrect.

Errors in the process of replication cause some mutations, but far from all of them. There is no meaningful sense in which a mutation is a “mistake”, because that word implies both a standard of correctness of replication and a mistake maker. Neither exists.

You speak as if the genome is deteriorating from some ideal state in the past. There is nothing to support that implication.

The problems of inbreeding are not related to any increase in the number or frequency of mutations in the genome. Instead, inbreeding results in a far higher phenotypic expression of deleterious recessive genes within a population than would normally be expected.

But the problem with Floodists is that anything that looks like solid proof that there was no Flood is just some miraculous fix by God that makes it LOOK like there was no Flood. Of course that means that God is being intentionally deceptive in the fake evidence he leaves in the physical world, but they seem perfectly happy with a lying God – starting with that lie about dying on the day you eat the fruit.

Yeah, and there’s a fairly large number of different things that would serve as such proof to any objective thinker.

There’s obvious stuff like biggest extinction event since life got started, glaciers and ice caps would have been destroyed, any surviving species would have had genetic bottlenecks at roughly the same time, post flood species geographic locations would lose any correlation with pre-flood locations of those species, distinct ecosystems in geographically isolated areas wouldn’t have had time to form, human civilizations that have history from before the time of the alleged flood, complete lack of any distinct worldwide geologic layer that would be expected from a worldwide event of that magnitude, etc.

Not to mention the lack of food afterward, for anything that managed to survive the flood event itself. If even a few members of a food chain get wiped out, the rest would have a major problem, and that’s with a calamity of a lot less magnitude that the one under discussion here.

Not to mention the conclusions that physicists produce when they calculate the amount of energy that would be released by the described event.

Henry

fittest meme said:

fnxtr - Your “no” answer to my first question sounds a little defensive. Couldn’t a flood have been what Melissa proposed as “the horrible disaster that killed off everyone but our family?” Even if the bottleneck was 10,000 couldn’t it have been a flood that caused it? If all humans alive today can be linked back to one male ancestor and one female ancestor, whatever the size of the bottleneck, only those directly descended from these ancestors would pass through. So I suppose that the bottleneck “could” be 10,000 individuals but the larger this number gets the more unlikely it becomes that every individual fits the criteria mentioned above.

I’m looking forward to an informed answer from Melissa.

The “horrible disaster” I mentioned was purely hypothetical for this example to illustrate how the “Most Recent Common Ancestor” is completely dependent upon who is alive now. In another 1000 generations, the MRCA of the mtDNA and Y chromosome will likely be different than they are now, due to which Y and mtDNA lineages are passed on, or lost.

Mark Sturtevant said:

Dr. Sayres: I think this recent cartoon from The Reason Stick is relevant to this posting. Mitochondrial Eve

Thank you, Mark!

fittest meme said:

Your right to note that the data doesn’t specifically imply 8 individuals but it certainly doesn’t eliminate the possibility. As I mentioned above it is more probable that the bottleneck is small than large in order to eliminate all humans who were not related to the common Y and mtDNA ancestor.

I’m looking forward to an informed answer from Melissa.

Using what we know about the observed variation across humans, and the rate at which changes accumulate (this holds for a variety of mutation rates), we can estimate when the common mtDNA ancestor and when the common chromosome Y ancestor lived.

We can build models of what we expect the variation within or across populations to look like under different models (with long or short bottlenecks, with severe bottlenecks, with population growth). Then we can compare our observations with these models and test which models are the most accurate description of the data.

fittest meme said:

apokryltaros said:

Historically speaking, there is plenty of evidence that there was no catastrophe of any kind that created a bottleneck among humans 4,000 years ago, what with, among other things, the Pyramids of Giza being under construction at the time.

I’m sure you do understand the lack of specificity involved with both contextual and Carbon 14 dating (how does one know that the charcoal pieces used to date the pyramids were not thousand of years old when they were used as fill?). And therefor you also understand why there is controversy among many archeologists and Egyptologists regarding the age of the pyramids.

Name and describe these alleged controversies concerning the dates of the Pyramids, please.

Regardless of this accuracy the pyramids are dated fairly close to the 4000 year ago date. If this is what you are counting on as your best evidence to support your statement that the bottleneck event happened “waaaaaaaaaaaaaaaaaaaaaaay beyond 4,000 years ago” I’m not impressed.

Actually, I’m using the Pyramids of Giza as evidence there was no magic flood that killed literally everyone and everything that could not, would not fit into Noah’s Ark 4,000 years ago. If you actually paid attention to what I was writing in the first place, evidence of the bottleneck occurring 140 to 70 thousand years ago is in the human genome.

If you understood genetics and biology, you would realize that a bottleneck of 8 individuals would leave very visible signs of inbreeding (either physical, genetic, or both) among their descendants …

If humans really were descended from Noah and his 3 sons, among other things, humans would be far more inbred, and would experience very few, and very poor reproductive successes today (especially if we were descended from 8 individuals 4,000 years ago).

There is Biblical evidence that you are right about this. Indeed the life spans of individuals were recorded to be much shorter after the flood than they were before. The effect would probably be even more problematic today since the human genome has acquired and passed on a great deal more mistakes (mutations) through many generations of copying. It is these mutations which are the reason inbreeding is a problem.

If you actually were a Biblical scholar, you would understand that the magically long lifespans of the various ancient Biblical patriarchs, i.e., Methuselah living for 900+ years, were imitations of the magically long lifespans ritually according to the various mythical founder-kings of various Mesopotamian cities.

apokryltaros said:

If you actually were a Biblical scholar, you would understand that the magically long lifespans of the various ancient Biblical patriarchs, i.e., Methuselah living for 900+ years, were imitations of the magically long lifespans ritually according to the various mythical founder-kings of various Mesopotamian cities.

Methus’lah lived nine hundred years,

Methus’lah lived nine hundred years,

But who calls dat livin’

When no gal will give in

To no man what’s nine hundred years?

– Ira Gershwin

Not to mention that Methusalah’s reported time of death was within a year of the alleged flood, which means he was evil! ;)

M. Wilson Sayres said:

2. The existence of a MRCA of the mtDNA and the existence of a MRCA of the Y chromosome does not imply a bottlenecks. As the video shows, it just suggests that we can trace back genomic regions (all genomic regions, in fact) back to their own common genomic region ancestor. But, there is no evidence that there was one person or two people whose genomes contained the ancestral state of all of our genomic regions.

Do I read you correctly in interpreting that the MRCA of the mtDNA is always one individual, and the MRCA of the Y chromosome is also always one individual ? That is by definition of the MRCA and has absolutely nothing to do with possible occurrence or absence of bottlenecks during the history of human populations.

M. Wilson Sayres said: In fact, all the evidence from the rest of the genome suggests the contrary - that we are composites of thousands of people (approximately 10,000).

Well, that could be an indication of a bottleneck, but it has nothing to do with the concept of the MRCA. There is no reason to think that the MRCA lived during the bottleneck.

I am a poor (pure) layman in this matter. I would like to know, how the information in the modern genomes was used to estimate the time to the most recent ancestor.

It appears to me that it would be impossible to use the definition of the MRCA, since we simply do not have enough information. We need to use proxies.

Using proxies is perfectly all right and can provide valuable information (with error limits).

M. Wilson Sayres said:

Haha, apparently it was a terrible judgement choice.

From my perspective it appeared to be good judgement when viewed in the context of a free, unencumbered pursuit of what is really true.

It was bad judgement when viewed in the context of an audience that finds certain logical inferences to be out of bounds.

Two courses of action seem to present themselves.

1. Know your audience and adjust your truth claims according to what is well received.

2. Trust sound logic and continue the pursuit of what is real despite the ridicule and persecution from those whose beliefs it threatens.

It’s a pretty significant crossroads.

fittest meme said:

M. Wilson Sayres said:

Haha, apparently it was a terrible judgement choice.

From my perspective it appeared to be good judgement when viewed in the context of a free, unencumbered pursuit of what is really true.

It was bad judgement when viewed in the context of an audience that finds certain logical inferences to be out of bounds.

Two courses of action seem to present themselves.

1. Know your audience and adjust your truth claims according to what is well received.

2. Trust sound logic and continue the pursuit of what is real despite the ridicule and persecution from those whose beliefs it threatens.

It’s a pretty significant crossroads.

If you’re thinking that the “crossroad” is that MWS is now open to YE creationism as a serious scientific alternative to evolution, I think you’d better think again.

fittest meme said:

2. Trust sound logic and continue the pursuit of what is real despite the ridicule and persecution from those whose beliefs it threatens.

The problem is that to present an alternative explanation, you need to present evidence coupled with rational, logical explanations.

Making violently vociferous quibblings concerning how your favorite misconceptions are really better than actual science, while angrily whining about not to hurt Creationists’ feelings do not make for an adequate substitute.

apokryltaros said:

fittest meme said:

2. Trust sound logic and continue the pursuit of what is real despite the ridicule and persecution from those whose beliefs it threatens.

The problem is that to present an alternative explanation, you need to present evidence coupled with rational, logical explanations.

And once I left home for university and could investigate more on my own, I concluded the evidence was against the YECism I grew up on so I became an ex-YEC.

I did get “ridicule and persecution” as fittest meme describes but it was from other YECs, including from friends and some family. Despite this, I “continued the pursuit” anyway.

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This page contains a single entry by M. Wilson Sayres published on August 8, 2013 7:15 AM.

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