Re: [asa] Two questions

To Mike Gene:

Regarding Question 1, I have some passages for you. They are from the 6th edition (1872) of The Origin of Species. I'll reproduce parts of them below.

I don't claim expertise in Darwin interpretation, but it seems to me that at least three main reasons pop out in these two passages:

1. Darwin believes that "ontogeny recapitulates phylogeny", and since, in the development of the embryo, no great leaps are observed, he finds it inconsistent that great leaps could have occurred in the course of evolution. (Ch. VII)

2. Darwin believed that inheritance was blended rather than particulate. This meant that any sudden great change would be slowly blended out of existence, as a single individual's genetic material would be watered down, generation after generation. So, for a "hopeful monster" to reproduce after its kind, it would need a mate, and that would mean that two hopeful monsters would have to occur at the same time. In fact, two would probably not be enough; a small breeding population would be needed; thus, several hopeful monsters. If the probability of one hopeful monster is astoundingly low, the probability of several occurring within a few years is infinitesimal. (Ch. VII)

3. Darwin noted the interaction of complex parts and systems in an organism, and reasoned that for a great leap to occur, a completely new organization would have to pop up, and that this would be wildly unlikely. (Chs. II, VII)

Regarding reason 3, note that Darwin was anticipating the "tornado assembling a 747 in a junkyard" objection to evolution, and saying that he agreed with the objection: evolution couldn't possibly work in that way. (Note also that reason 3 employs essentially Paleyesque-ID type reasoning, including the analogy to machines, so that if the core arguments of Paley and ID are to be banned from the schools as "religious", one of Darwin's own arguments against gradualism must also be banned from the schools as "religious".)

---
The passages:
Chapter II, second paragraph:
It may be doubted whether sudden and considerable deviations of structure such as we occasionally see in our domestic productions, more especially with plants, are ever permanently propagated in a state of nature. Almost every part of every organic being is so beautifully related to its complex conditions of life that it seems as improbable that any part should have been suddenly produced perfect, as that a complex machine should have been invented by man in a perfect state. 
Chapter VII, last six paragraphs (first five omitted; the last paragraph summarizes the others):
.........
He who believes that some ancient form was transformed suddenly through an internal force or tendency into, for instance, one furnished with wings, will be almost compelled to assume, in opposition to all analogy, that many individuals varied simultaneously. It cannot be denied that such abrupt and great changes of structure are widely different from those which most species apparently have undergone. He will further be compelled to believe that many structures beautifully adapted to all the other parts of the same creature and to the surrounding conditions, have been suddenly produced; and of such complex and wonderful co-adaptations, he will not be able to assign a shadow of an explanation. He will be forced to admit that these great and sudden transformations have left no trace of their action on the embryo. To admit all this is, as it seems to me, to enter into the realms of miracle, and to leave those of Science.
I can send you the remaining paragraphs privately if you like, or you can just get them off the complete works of Darwin web site, as I did.
  ----- Original Message ----- 
  From: Nucacids 
  To: asa@calvin.edu 
  Sent: Wednesday, April 15, 2009 12:00 AM
  Subject: [asa] Two questions
  Let me quote from Eugene Koonin's recent paper, "Darwinian evolution in the light of genomics" (Nucleic Acids Research, 2009, 1-24). These are twp excerpts from where he is outline the principal concepts of the Modern Synthesis.
  "Evolution proceeds by fixation of the rare beneficial variations and elimination of deleterious variations: this is the process of natural selection that, along with random variation, is the principal driving force of evolution according to Darwin and the Modern Synthesis. Natural selection which is, obviously, akin to and inspired by the 'invisible hand' (of the market) that ruled economy according to Adam Smith, was the first mechanism of evolution ever proposed that was simple, plausible, and did not require any mysterious innate trends. As such, this was Darwin's second key insight. The founders of population genetics, in particular, Sewall Wright, emphasized that chance could play a substantial role in the fixation of changes during evolution not only in their emergence, via the phenomenon of genetic drift that entails random fixation of neutral or even deleterious changes. Population-genetic theory indicates that drift is particularly important in small populations that go through bottlenecks (6,16). However, the Modern Synthesis, in its 'hardened' form (13), effectively, rejected drift as an important evolutionary force, and adhered to a purely adaptationist model of evolution (17)."
   
  And
   
  "The beneficial changes that are fixed by natural selection are 'infinitesimally' small, so that evolution proceeds via the gradual accumulation of these tiny modifications. Darwin insisted on strict gradualism as an essential staple of his theory: 'Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being . . . If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.' [(1), chapter 6]. Even some contemporaries of Darwin believed that was an unnecessary stricture on the theory. In particular, the early objections of Thomas Huxley are well known: even before the publication of the Origin Huxley wrote to Darwin ''You have loaded yourself with an unnecessary difficulty in adopting Natura non facit saltum so unreservedly' (18)." 
   
  Here are my two questions: 
   
  Why did Darwin insist on strict gradualism as an essential staple of his theory?
   
  Why did most proponents of the Modern synthesis reject drift as an important evolutionary force, and adhered to a purely adaptationist model of evolution?
   
  - Mike 
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