The time scale of the bottleneck?

(Chris) #21

I am able to accept that God is perfectly capable of using evolution to create life on Earth.
But I don’t think he did.

(Matthew Pevarnik) #22

George what am I missing? There were some migration bottlenecks of ~500 people or so within the pas 50,000 years but there is no evidence of any serious Homo sapien bottleneck, not even going back to common ancestors with chimpanzees. I’m not sure what we are discussing here. Are you talking about Y-chromosome Adam which here is a summary of some different methods:

(Randy) #23

@aarceng Brother Chris , I appreciate your congenial way of discussing things. It’s always good to have iron sharpening iron.



In the course of the conversation Richard did change his opinion on the % of similarity. So I noticed 2 things about his final comment way down at post 120. He no longer mentions a lower bound on his range estimate and admits that 95% is possible (otherwise it wouldn’t count as a prediction) but not yet an “established fact”. So perhaps instead of reasonable I should have said possible. Not much difference in my mind.

If I might ask, what do you think is the significance of a similarity of 93.4% or greater with the chimp?

(Mitchell W McKain) #25

It seems to me that all the evidence including migration, Y-chromosomal Adam and mitochondrial Eve all agrees with a long bottleneck in the human population in southern Africa between 100,000 and 200,000 years ago, which could have gone as low as 2000 people. There is additional evidence of a migratory bottleneck from a migration across the Bering strait which could have been as few as 70 people. This, of course, rejects the Toba catastrophe hypothesis which the evidence hasn’t supported. This also seems to be the origin of modern homo-sapiens species which agrees with the logical link between low population and high genetic drift.

It seems to me the chart given for different estimates of the time for Y chromosomal Adams seems to agree rather well with this. The estimates place this as no more recent that 100,000 years ago and a few push this back to as far as 250,000 years ago. And it should be noted that older estimates do not logically disagree with the long bottleneck hypothesis 100,000 to 200,000 years ago.

(Matthew Pevarnik) #26

What do you mean by ‘long bottleneck?’ I haven’t seen any papers with a bottleneck of 2,000 some people besides regional bottlenecks involving migration but not for the human genome as a whole. Could you point me to something you are looking at?

(Stephen Matheson) #27

This is an almost hopeless muddle. Neither Y-chr Adam nor mito Eve has anything to do with bottlenecks. I have personally never heard of a “long bottleneck” in southern Africa, though I do know of some old-ish theorizing about the species riding out a rough stretch by eating a lot of shellfish in Africa. Not my area, but I think that’s pretty speculative. No matter what, you should be wary of any discussion of bottlenecking that uses Y-Adam or mito-Eve as evidence. That’s a basic error.

(Mitchell W McKain) #28

That’s funny… since a google search brings these up quite easily.

Incorrect. At the most you can say this is weak evidence. It is just that there is a higher probability of having these during a genetic bottleneck than at other times. I don’t think it is a coincidence that the estimates of these two fall in the same time frame.

I think there is a bit of over-reacting involved in this subject. The idea that ANY of this supports the idea of humanity coming from two people is absurd. But that doesn’t mean we have lean over backwards to ignore any evidence of a genetic bottleneck at all. Like I mentioned, it is just plain logic that you are going to expect the greatest genetic change in small populations on the brink of extinction and we have the homo-sapiens species appearing in just the right time frame to fit all of this. Sure it is speculative and I am not a biologist who has to be oh-so careful not to go too far from what can be proven without a doubt. I am just a dilettante willing to place my bets where the probability points best.

Yes, I read that article. And this is a part of the body of evidence I am talking about. I am also talking about all the migration and linguistic evidence that tells a story of human migration from southern Africa to the rest of the world.

Compared to my own area of physics, all of this stuff looks pretty speculative to me. Not that physics doesn’t have a few areas ripe with speculation.

(Stephen Matheson) #29

I found this old review article discussing the long-neck bottle(neck) idea. It predates large scale genomics. I don’t know whether it is still considered plausible or not but I suspect we have much more data by which to judge such ideas. Your claims, which I was responding to, seem to be a melange of different ideas, of varying quality (the ~2000 individuals thing is not a specific part of the long-neck idea, as near as I can tell).

You are making an error. There is no necessary connection between a common ancestor and a bottleneck. None. Pick any common ancestor you want; we could use you and me. Identify that common ancestor. Then postulate a bottleneck? Why? It’s an error, and it creates a lot of confusion.

(Mitchell W McKain) #30

I didn’t say there was a necessary connection. Your soapbox is not my problem. What I said is that there is a higher probability of having a Y-chromosomal Adam and mitochondrial Eve during a genetic bottleneck than at other times. This is just simple logic. Do I really have to demonstrate this to you, because I have math skills to do so if you insist.

This is a discussion of a very different genetic bottleneck, long before the appearance of modern homo-sapiens. That there are more such periods in our evolutionary history is something that I would expect.

(Chris) #31

I must have missed it. Can you point me to the post where he said that? Until then I will assume that his estimate of between 84.4% and 93.4% still applies.

(Chris) #32

Robert W. Carter and Matthew Powell have done a study using a “population modelling program designed to examine changes in allele frequency within ‘biblical’ populations.” A special program had to be written because other programs can’t handle the low population numbers, stochastic modelling, and level of detail required for such an analysis. They conclude that “skeptical claims that biblical models are excluded by population genetics are unwarranted.”

The genetic effects of the population bottleneck associated with the Genesis Flood

(Matthew Pevarnik) #33

Really? The models by experts in population genetics can’t handle small populations, stochastic modeling and any level of detail… but for those who don’t even publish in real scientific journals they can do it?!?

(Chris) #34

Genetic fallacy.

(Matthew Pevarnik) #35

If you insist. Does their paper need addressed? They imagine that with a bottleneck of 8 4,000 years ago you can end up with the genetic diversity that we have today. That would require at least an increase of the mutation rate of humans of 100x sustained for thousands of years beyond what we observe at the present, not to mention all of the shared ERV and Alu and other insertions that we share with our closest genetic relatives (chimpanzees). If they have a good idea, publish it in a real scientific journal and let it be hashed out there.


Read the thread. I don’t have the expertise or time needed to condense the technical details.

In his final wrap-up post he drops the minimum bound and admits the 95% was a possibility. Something he wasn’t willing to accept at the beginning of the exchange.

Sorry that I can’t point you to the single sentence where he says this.

(Chris) #37

Well I didn’t find it so I will assume you were mistaken.

(Matthew Pevarnik) #38

@Bill_II Here is @RichardBuggs final post on the topic:

where he concludes:

I would accept 95% as a prediction, but not as a statement of established fact.

But the percent similarity is not really that useful and a nice summary from @DennisVenema:

(Chris) #39

Where he says,

He is certainly not accepting 95% and I found nowhere where he revised his earlier estimated range of between 84.4% and 93.4%.

I agree. Since humans are mammals then it is to be expected that since we share many tissues, organs, etc., we would have a high degree of genetic similarity.

On the other hand how much genetic difference could have accumulated since the hypothetical split from our common ancestor with the chimp about 7 million years ago? (or is it 5 million, or maybe 13 million?). Can you tell me that? If the genetic difference is less than that figure then perhaps the hypothesis is possible; but what if the genetic difference is greater? Perhaps 95% similarity (5% difference) is already more than can be supported by evolutionary theory.

(Matthew Pevarnik) #40

I’ll leave one explanation up to @glipsnort:
Evolution is a faith because common ancestry doesn't add up

Also from his article I linked earlier the genetic difference in humans that’s due to random mutations looks like this:

And this difference between humans and chimpanzees looks like this:

The pattern is identical and it mainly just differs in scale. The y-axis is higher in the human-chimpanzee graph than human-human. But because the overall pattern is conserved, that means that the same mechanism of leading to diversity among humans - i.e. random mutations is the main mechanism leading to diversity between the human and chimpanzee lineages. There’s simply just been more time since a common ancestral population.