Two Questions

Let me quote more extensively from Koonin’s paper:

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).


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).

Now, let’s ponder two important 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?



3 responses to “Two Questions

  1. Michael,

    Hope u had good holidays, happy Pesach or Easter.

    First why question, Gradualism. I do not have Darwin’s Origins handy. But I’ll take a stab. Refreshing my memory, he actually changed his views on gradualism over time, due to critics, even important supporters like Huxely. So, what did he mean by “gradualism” after several publications? This is argued over fiercely today by Darwinist. I’m curious what you think. It appears he let go of constant rates.

    Without a gradualistic step by step process as Darwin said it would render his theory a failure. Because he staked his claim to a TOL that was based upon Commen Ancestory. If the steps were not gradual, then the historical records would be nearly impossible to determine in my estimation. He was convinced at the time of the geological record which had come to the forefront. Was it Lyell’s book that influenced him on his trip? Yep, Uniformitarianism. But now I don’t know if he was a strict uniformitarian after a quick review.

    At any rate, this may not be his specific reason. But if the steps are not gradual, then it becomes problematic with leaps and jumps to connect the branches of the tree of life. Without insight to molecular and gentic codes, they were stuck with morphology. The anatomy, organs however were difficult to explain at the time thru leaps. Gradulism also did away with design. By small steps, randomly aquired and fixed through natural selection, it bypasses any possible design option, he thought at the time – I assume.

    Since he had little mathematical understanding in comparison to Mendel, he also suffered to understand geneticsl. At the time, he knew transitional forms were key to link together all the disparate fossils on record. And he needed there to be many transitional forms for natural selection to be a strong force.

    A large jump in information however from one branch to the next allows for teleology and renders natural selection moot. It loses importance as one of the pillars in his theory.

    Am I close?

    Question two may have to wait until tomorrow. Thanks for reviewing this and Koonins paper.

  2. Michael,

    Question Two: Drift…

    A quick search turns up controversy, much like arguments I found on gradualism.

    Simple answers I found…
    Because genetic drift is truly random, unpredictable, across all populations.

    It can reduce genetic variation, therefore limit Natural Selections power for adaptation. Without adaptation to stress or environment, evolution/adaptation breaks down, so Genetic Drift is a mechanism of varying limitations.

    However, Modern Synthesis evolutionist still consider it a basic mechanism of evolution.

    But here is an interesting quote:

    “Drift by its very nature cannot be positively demonstrated. To do this it would be necessary to show that selection has definitely NOT operated, which is impossible. Much indirect evidence has been obtained, however, which purports to favour the drift position. Firstly, and in many ways most persuasively is the molecular and biochemical evidence…” (Harrison, G.A., Tanner, J.M., Pilbeam, D.R. and Baker, P.T. in Human Biology 3rd ed. Oxford University Press 1988 pp 214-215)”

    Admittedly, this was quoted from Moran,, last updated 1993.

    An adaptation model, along with gradualism allows for non-teleological process from the bottom up. Drift can lead to rapid extinction and is a totally random process.

    Those who assert(ed) an adaptionist model are also asserting Natural Selection as the primary directive of evolutionary change.

    Gould and Lewontin provided the now “famous” scourging, introducing PuncE as an alternative to the Adaptation model.

    quotes and material referenced from… Evo 101, TalkOrigins, & Workshop.

  3. I might add, Gould and Lewontin pushed for a evolutionary view of “plurality”

    I know that Doolittle favors this position. I assumed Koonin does as well since he recognizes HGT as yet another mechanism for change.

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