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Author Topic:   Human Chromosome 2 and the Evolution of Humans
Dr Adequate
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Posts: 16107
Joined: 07-20-2006


Message 3 of 56 (667903)
07-13-2012 12:40 PM
Reply to: Message 1 by herebedragons
07-12-2012 11:18 AM


I don't see why this variation shouldn't have undergone fixation through genetic drift just like any other variation can.

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 Message 1 by herebedragons, posted 07-12-2012 11:18 AM herebedragons has responded

Replies to this message:
 Message 8 by herebedragons, posted 07-18-2012 10:21 AM Dr Adequate has responded

  
Dr Adequate
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Posts: 16107
Joined: 07-20-2006


Message 12 of 56 (668238)
07-18-2012 7:27 PM
Reply to: Message 8 by herebedragons
07-18-2012 10:21 AM


At first I didn't consider genetic drift to be much of a factor since the probability of fixation seemed unrealistic. But your comment gave me cause to think about it a bit closer. If the population group that the mutation occurred in was rather small, say <100 time?

Actually, it's rather neat how it works out. If you have a larger population, then the probability of a neutral mutation being fixed is that much smaller. But the probability of it happening is that much bigger. And these effects, if you do the math, cancel out exactly, giving us the nice result that if all mutations were neutral (which is a good first approximation to the truth) the rate of fixation of mutations in the gene pool per generation is exactly equal to the rate of mutation in the individual.

So yes, a large population makes it more unlikely that any particular balanced translocation will get fixed, but it also means that there are that many more balanced translocations which will arise and so be candidates for fixation, and these two effects will exactly cancel one another out. Therefore, if we knew how often balanced translocations happen to individuals (and I'm not sure that we do) then we could also say the rate at which we'd expect them to become fixed in the population, and this would be completely independent of the size of the population.

So if you ask yourself: "What were the chances of this balanced translocation being fixed by genetic drift?" then population size is important; but if you ask yourself: "What were the chances of a balanced translocation being fixed by genetic drift?" then it isn't.

Edited by Dr Adequate, : No reason given.


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Dr Adequate
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Posts: 16107
Joined: 07-20-2006


Message 18 of 56 (668324)
07-19-2012 8:42 PM
Reply to: Message 13 by herebedragons
07-19-2012 10:19 AM


Yes, but in this case we are talking about a specific mutation. [...] But IMHO, in order to be conclusive there needs to be a plausible explanation.

Yes, but the explanation, though plausible, is allowed to be very unlikely with respect to the specific mutation, because there must have been lots of this kind of mutation which, as it happened, didn't get fixed.

So, for example, I don't think we necessarily need to provide an explanation "without invoking another spontaneous B-T". Why not invoke another? That would help explain why this particular one got fixed and all the others didn't. Nor can we rule out other forms of "dumb luck", as you call it. It is perfectly plausible that this was the one single balanced translocation that got lucky between the common ancestor of apes and the array of modern species we have now. All the fusions of different chromosomes in different branches of the apes didn't make it. One did. That suggests that there was an element of luck, a fluke event and not a predictable one.


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Dr Adequate
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Posts: 16107
Joined: 07-20-2006


Message 27 of 56 (671870)
08-31-2012 12:50 AM
Reply to: Message 23 by foreveryoung
08-30-2012 11:41 PM


I agree that there is no evidence for a GLOBAL flood 4350 years. In fact, all the evidence is against it. I am starting to believe in a mesopotamian flood around that time that destroyed the sumerian culture. I should have posed my question differently though. Would it be possible to have a thriving human population after 4350 years if it started with only 7 humans such as noah's family?

Maybe. Coyote's point (and mine on the other thread) was that the human population couldn't be as genetically diverse as it is now. Could it be as large as it is now? I don't really see why not, assuming they weren't wiped out by genetic problems associated with inbreeding. But it would not look, in detail, like the human population that we actually have.


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Dr Adequate
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Posts: 16107
Joined: 07-20-2006


(2)
Message 33 of 56 (671887)
08-31-2012 4:05 AM
Reply to: Message 31 by foreveryoung
08-31-2012 2:41 AM


Re: Any wiggle room?
I don't think an exact number matters but I will stick with that figure for arguments sake. The point is whether or not it is possible to grow a human population of significant size from just 7 people in a short amount of time.

Yeah, why not? Let's take the interval between generations to be 30 years, and take the flood to be 4000 years ago. That gives us 133 generations. In that time, we'd want to multiply the size of the human race by about a billion. So you'd want the average number of (surviving and then marrying) children per couple to be about 2.3. So it's biologically possible.

The only fly in the ointment is that human populations haven't in fact grown that fast over most of human history, but since we're taking Noah's Flood as a hypothesis, I guess we're not worrying too much about historical accuracy.


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Dr Adequate
Member
Posts: 16107
Joined: 07-20-2006


Message 45 of 56 (671939)
08-31-2012 5:29 PM
Reply to: Message 39 by foreveryoung
08-31-2012 10:03 AM


Re: Any wiggle room?
So, it is possible. How do we know how fast global human populations grew in the past? From the biblical records, the families of each generation appear to be quite large.

From the same "biblical records" the time between generations was hundreds of years. I'm beginning to think that these "biblical records" maybe aren't all that accurate.

Also, the largest family I can remember in the Bible is that of Jacob. Twelve children in a family? Yes, but he had two wives and two concubines. That makes it rather easier. To look at what that really means in terms of population growth, we'd have to figure in the three men who were single because Jacob was hogging all the women; when you do that it took eight people to produce a family of twelve.

To estimate actual population sizes we can use archaeology to look at things like settlement sizes, we have historians noting the size of this or that city, we have actual censuses taken at various times.


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