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Ch. 2: An Idea is Born 
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 Ch. 2: An Idea is Born
Ch. 2: An Idea is Born


Please use this thread to discuss the above listed chapter of "Darwin's Dangerous Idea: Evolution and the Meanings of Life" by Daniel Dennett.



Thu Feb 16, 2017 11:53 pm
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Post Re: Ch. 2: An Idea is Born
I mentioned on the "will participate" thread that I am dissatisfied with Dennett's basic presentation of natural selection in Ch. 2. Re-reading it to clarify my ideas, I don't really object to his presentation, but would add in some important factors.

He is anxious to demonstrate that there is a mechanism available to make "descent with modification" a viable option. I think that is a worthy point, and his explanation of it is sound. In particular I like his note that the mechanism of natural selection provided Darwin both with a "hunting license" and a guide to which questions to ask.

The conclusion he might have followed with is that Darwin's observations in the Galapagos Islands illustrate both: Darwin was primed to find "descent with modification" and therefore realized that the several varieties of finches were descended from a common finch ancestry, and he could look for adaptation to explain the different beaks for different food niches, for example.

However, in the material on the workings of natural selection, his notion that it is "always crunch time" appears to suggest that a superior adaptation will therefore be heavily favored reproductively, at least over long periods of time. While he does not say "heavily favored" and explicitly allows for a small differential, his use of "crunch time" and his ways of phrasing suggest that he thinks selective pressures are strong. This is going to create problems when he gets to speciation.

The problem is that mutations providing improvement are going to spread within a population faster than their differential reproduction effect weeds out those without the mutation. So if there is a mutation that matters, it is very likely to be incorporated into the entire genetic stock of the species. Obviously this does not conflict either with natural selection, descent with modification, or Dennett's presentation, but it does mean that speciation remains a challenge to explain.

That's why the Berkeley diagrammatic presentation on punctuated equilibrium is important.
http://evolution.berkeley.edu/evolibrar ... ctuated_01
It incorporates geographic isolation with a pronounced change in selective pressure to explain speciation. Both are necessary. And the combination happening at the same time may be more frequent than the introduction of mutations which offer potential only for success within a new niche. The combination of speciation requirements is certainly more frequent than its subset combining these requirements with helpful mutations.

So it should not come as a shock to hear that the incorporation of random mutations may not be the source of speciation at all. The differences between bears, cats, dogs and raccoons may not have, at any point, incorporated mutations, but may have relied instead on selective pressures among variation already present in their common ancestors.

If that seems odd, consider the large number of examples available of "convergent evolution," in which creatures from different lineages acquire similar traits (mammals become like birds: = bats; flightless birds exploit the same niches as long-legged mammals; seals and fishing birds take on the tapered shapes of barracudas and other smallish predatory fish; etc.) to adapt to the same ecological niche. If such events each depended on a lucky mutation (most mutations are neutral, and those which actually affect the animal's survival or reproduction are mostly disasters) one suspects we would not see convergent evolution nearly as frequently.

So the point is, mutation is all well and good, but variation is the real raw-material of genetic change.



Mon Feb 20, 2017 11:53 am
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Post Re: Ch. 2: An Idea is Born
Harry Marks wrote:
I mentioned on the "will participate" thread that I am dissatisfied with Dennett's basic presentation of natural selection in Ch. 2. Re-reading it to clarify my ideas, I don't really object to his presentation, but would add in some important factors.
Hello Harry, thank you for these comments. I have not yet read the chapter but your discussion inspires me. I am particularly interested in the theme of the logic of causality, how the nature of matter requires necessary facts of causal evolution.
Harry Marks wrote:
He is anxious to demonstrate that there is a mechanism available to make "descent with modification" a viable option. I think that is a worthy point, and his explanation of it is sound. In particular I like his note that the mechanism of natural selection provided Darwin both with a "hunting license" and a guide to which questions to ask.
This term ‘a hunting licence’ is central to the scientific method, in generating hypotheses which are confirmed by accurate predictions.
Harry Marks wrote:
The conclusion he might have followed with is that Darwin's observations in the Galapagos Islands illustrate both: Darwin was primed to find "descent with modification" and therefore realized that the several varieties of finches were descended from a common finch ancestry, and he could look for adaptation to explain the different beaks for different food niches, for example.
The hypothesis of evolution is confirmed by the evidence of the finches’ beaks demonstrating descent with modification.
Harry Marks wrote:
However, in the material on the workings of natural selection, his notion that it is "always crunch time" appears to suggest that a superior adaptation will therefore be heavily favored reproductively, at least over long periods of time. While he does not say "heavily favored" and explicitly allows for a small differential, his use of "crunch time" and his ways of phrasing suggest that he thinks selective pressures are strong. This is going to create problems when he gets to speciation. The problem is that mutations providing improvement are going to spread within a population faster than their differential reproduction effect weeds out those without the mutation. So if there is a mutation that matters, it is very likely to be incorporated into the entire genetic stock of the species. Obviously this does not conflict either with natural selection, descent with modification, or Dennett's presentation, but it does mean that speciation remains a challenge to explain.
Sorry Harry, I do not understand your statement that “mutations providing improvement are going to spread within a population faster than their differential reproduction effect weeds out those without the mutation.” I would have thought by definition these two rates are the same.
And then the process of incorporation will vary, depending on what the Berkeley diagram terms “peripatic speciation” (mixing by walking around).
Harry Marks wrote:
That's why the Berkeley diagrammatic presentation on punctuated equilibrium is important.
http://evolution.berkeley.edu/evolibrar ... ctuated_01
It incorporates geographic isolation with a pronounced change in selective pressure to explain speciation. Both are necessary.
’Necessary’ seems too strong. I would have thought a mutation could generate radiating speciation without isolation.
Harry Marks wrote:
And the combination happening at the same time may be more frequent than the introduction of mutations which offer potential only for success within a new niche. The combination of speciation requirements is certainly more frequent than its subset combining these requirements with helpful mutations. So it should not come as a shock to hear that the incorporation of random mutations may not be the source of speciation at all. The differences between bears, cats, dogs and raccoons may not have, at any point, incorporated mutations, but may have relied instead on selective pressures among variation already present in their common ancestors.
There is a constant mutation rate, and this input is necessary to throw up the occasional adaptive change, together with geographic opportunity. Cats are not dogs.
Harry Marks wrote:
If that seems odd, consider the large number of examples available of "convergent evolution," in which creatures from different lineages acquire similar traits (mammals become like birds: = bats; flightless birds exploit the same niches as long-legged mammals; seals and fishing birds take on the tapered shapes of barracudas and other smallish predatory fish; etc.) to adapt to the same ecological niche. If such events each depended on a lucky mutation (most mutations are neutral, and those which actually affect the animal's survival or reproduction are mostly disasters) one suspects we would not see convergent evolution nearly as frequently.
That does not make sense to me. Evolution by cumulative adaptation is the causal process whereby any good mutation spreads through the gene pool. Effective mutations can be extremely rare, but the beauty of evolution is that if say one in a million mutations confers benefit, however small, the causal process means it is precisely that mutation that will spread. And such mutations are conceptually distinct from variations. Bears are not raccoons.
Harry Marks wrote:
So the point is, mutation is all well and good, but variation is the real raw-material of genetic change.
Does Dennett actually argue that? My assumption was that variation without mutation was not sufficient for any speciation. Without mutation, the lines will still be able to deliver fertile offspring, so mutation seems to be a basic need for any speciation.


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Last edited by Robert Tulip on Tue Feb 21, 2017 3:32 pm, edited 1 time in total.



Mon Feb 20, 2017 5:07 pm
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Post Re: Ch. 2: An Idea is Born
Robert Tulip wrote:
Harry Marks wrote:
This is going to create problems when he gets to speciation. The problem is that mutations providing improvement are going to spread within a population faster than their differential reproduction effect weeds out those without the mutation. So if there is a mutation that matters, it is very likely to be incorporated into the entire genetic stock of the species.
Sorry Harry, I do not understand your statement that “mutations providing improvement are going to spread within a population faster than their differential reproduction effect weeds out those without the mutation.” I would have thought by definition these two rates are the same.

You are correct, and I apologize. I will try to be more patient in preparing my explanations. The point I was after was that (helpful) mutation does not naturally lead to speciation, but simply fills the population already there with its superior trait.
Robert Tulip wrote:
And then the process of incorporation will vary, depending on what the Berkeley diagram terms “peripatic speciation” (mixing by walking around).

I'm not sure, but I think that peripatric speciation is more about the small size of the separated group than about drift over time within separated groups, which is the hallmark of the allopatric kind of speciation. The punctuated equilibrium folk tend to emphasize peripatric speciation as the source of real innovation in genetic stock because the high selection pressure can drive a rapid rate of change in a characteristic. So if we are looking for a cause of a dramatic development such as the panda's thumb (a regular hand bone elongating to better strip bamboo,) for example, small populations are a likely place to look. The small population also makes for an absent fossil record of intermediate forms, but that is a side effect to the main argument.
Robert Tulip wrote:
Harry Marks wrote:
It incorporates geographic isolation with a pronounced change in selective pressure to explain speciation. Both are necessary.
’Necessary’ seems too strong. I would have thought a mutation could generate radiating speciation without isolation.

On reflection, I think you are probably right. However, I suspect such episodes are quite rare. Radiating speciation happens when there has been a big change in fit between morphology of the organism and rewards of the environment. This could be due to penetration to a new ecological niche, or due to dramatic changes in the niche already occupied, or due to dramatic new availability of a morphology within a species.

Since I believe most innovative speciation is due to extension of the possibilities already present, rather like breeding bigger and bigger dogs, I don't expect the fossil record to show many cases of a mutation leading to radiating speciation. Which is more likely, that a few finches found their way to the Galapagos before any breeding group of other birds, or that a mutation came along which made finches somehow suitable to the Galapagos?
Robert Tulip wrote:
There is a constant mutation rate, and this input is necessary to throw up the occasional adaptive change, together with geographic opportunity. Cats are not dogs.

Yes, there is a constant mutation rate, used to calculate "genetic clocks". However, genetic clock calculations have to deliberately exclude mutations having much to do with survival, since natural selection will generally edit out most such mutations. There is a common belief that adaptive change can only come from the mutations which occur, and which will presumably include an occasional helpful one. A bit of reflection will demonstrate that this is not necessarily so.

If the current population variation includes differences in ability to get by on two legs for a ways (as dog owners will attest that it does) and there is suddenly a new selective pressure for two-leggedness, (reaching a fruit that emerges within the climate, or stowing game out of reach of invading populations of hyenas, or whatever), within not many generations the population will include mostly those with exceptionally good two-leggedness. The real innovation happens when such a dramatic shift begins to create selective pressure on other traits, such as tool use or management of fire.

Such chains of innovation can happen without any new variation being introduced. I suspect they mostly do: at one point there was a common ancestor between cats and dogs, and I doubt seriously if a "cat mutation" created the difference. Might have, but peripatric speciation provides an explanation which, on the face of it, seems more likely to be frequent over the history of life.
Robert Tulip wrote:
Harry Marks wrote:
If that seems odd, consider the large number of examples available of "convergent evolution," in which creatures from different lineages acquire similar traits. ... If such events each depended on a lucky mutation ... one suspects we would not see convergent evolution nearly as frequently.
That does not make sense to me. Evolution by cumulative adaptation is the causal process whereby any good mutation spreads through the gene pool. Effective mutations can be extremely rare,
Wikipedia cites several cases of dramatic adaptive radiation. One of them is the evolution of a fourth cusp in mammalian teeth, which arose several distinct times and each time led to a radiation. That strikes me as plausibly due to mutation, but it seems possible it was also an occasional change resulting from the variation already present, as if it was the length of a thigh bone. Is a sixth toe in humans a mutation? Or is it just an occasional accident within the variation of widths of feet and sizes of toes? I am not a geneticist so I can't tell you, and it may turn out to be only a semantic issue, but I suspect that significant shuffling of the ecological niches happens more often than significant helpful innovations.
Robert Tulip wrote:
such mutations are conceptually distinct from variations.
Well, I think that's why I am going on about it. Variations plus peripatric speciation provide a plausible mechanism for something typically ascribed to mutation.
Robert Tulip wrote:
Harry Marks wrote:
So the point is, mutation is all well and good, but variation is the real raw-material of genetic change.
Does Dennett actually argue that? My assumption was that variation without mutation was not sufficient for any speciation. Without mutation, the lines will still be able to deliver fertile offspring, so mutation seems to be a basic need for any speciation.
Maybe you are referring to the gradual loss of interbreeding between geographically isolated subspecies, the basis of allopatric speciation. That is indeed caused by apparently random mutations. So if there are that many innocuous mutations, maybe the rate of favorable mutations is not so incredibly low. However, the conditions for peripatric speciation strike me as a more common occurrence. And peripatric speciation is not only likely to work by means of variation without mutation, but provides what is, in my mind, a more plausible source of the innovative speciation which occasionally separates the dogs from the cats.

Basically, my complaint against Dennett's presentation is that he not only ignores variation as raw material, but in his emphasis on "always crunch time" makes it seem as if variation must constantly be being weeded out by selection. Not only does that not square with casual observation, but it distorts the account of speciation.



Last edited by Harry Marks on Tue Feb 21, 2017 2:02 pm, edited 1 time in total.



Tue Feb 21, 2017 12:33 pm
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Post Re: Ch. 2: An Idea is Born
Borrowing Dexter's link from another thread because this seems a more appropriate place to respond.

Dexter wrote:
Nagel's book "Mind and Cosmos" has the subtitle "Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False."

Here he is getting wrecked in some book reviews:

https://whyevolutionistrue.wordpress.co ... -pummeled/

Granted I'm reading comments about a book I haven't read, but Nagel seems to be advocating something teleological in the evolution process. That is, evolution is directed toward certain goals (e.g., consciousness) by a process we don’t understand. It seems to me that Dennett puts this idea to rest in chapter 2 of his book. That the algorithms in natural selection are decidedly NOT to produce us. He demonstrates this very well with the idea of a coin toss tournament, the winner of which will have won 25 coin tosses in a row, which seems mathematically improbable, but absolutely necessary if the algorithm is set up that way. As such, when you come across the perfect grace and speed of a leopard or the perfect symmetry of a butterfly, it's not hard to imagine some Mind at work, but it really is just the mindless power of the algorithms underneath the engine of natural selection (and other selection pressures too).


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Post Re: Ch. 2: An Idea is Born
Agreed, it looks like Dennett address this in more detail towards the end of the book, but I doubt that he is making any controversial claims about "goals" of evolution



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Post Re: Ch. 2: An Idea is Born
geo wrote:
Nagel seems to be advocating something teleological in the evolution process. That is, evolution is directed toward certain goals (e.g., consciousness) by a process we don’t understand.

I haven't read the Nagel material, but if that is his argument, I doubt that he has done any better with it than previous efforts.

geo wrote:
It seems to me that Dennett puts this idea to rest in chapter 2 of his book. That the algorithms in natural selection are decidedly NOT to produce us. He demonstrates this very well with the idea of a coin toss tournament, the winner of which will have won 25 coin tosses in a row, which seems mathematically improbable, but absolutely necessary if the algorithm is set up that way.
I am much more impressed by evidence that has been used, such as intermediate forms found where the theory would predict them. There is nothing wrong with Dennett's argumentation, but in the end, a claim that "mind" or "purpose" must be hidden in the process is a claim that no mechanism could have done it. So I am most persuaded by being shown a mechanism that could have done it. The claim for "irreducible complexity" of the bacterial flagellum is an example.

I do like the coin toss example. Dennett seems to be setting up several parts of a complex arrangement of ideas, but I cannot tell if he is going to use the "reversal of perspective" involved in the coin toss argument (a more complex version of it is the Black Swan argument of Nassim Taleb) or if it is a one-time swing at teleological arguments.



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Post Re: Ch. 2: An Idea is Born
Dangerous ideas Darwin....really interesting title...heard about its law but dangerous.....really look weird...how it could be possible.....because I read about its laws when i was in College...then to know its ideas,,when i was searching online book store..then i reach to infibeam.com...there i search that name and find the books....now i am curious to read whole books.



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