The Frailty of Adaptive Hypotheses

Earlier I noted that Michael Lynch has doubts about whether natural selection was responsible for the evolution of multicelluarity:

These results, along with our theoretical work on network evolution, challenge the popular idea that modularity arises as a direct consequence of selection for morphological complexity, and by extension raise questions about the common assumption that natural selection was responsible for the emergence of multicellularity.

A couple of years ago, Lynch published a very interesting article entitled, “The frailty of adaptive hypotheses for the origins of organismal complexity” in PNAS (2007) vol. 104, pp. 8597–8604.  You can read the article here.

A couple of excerpts relevant to the evolution of multicellularity are below the fold.

The vast majority of biologists engaged in evolutionary studies interpret virtually every aspect of biodiversity in adaptive terms. This narrow view of evolution has become untenable in light of recent observations from genomic sequencing and population genetic theory. Numerous aspects of genomic architecture, gene structure, and developmental pathways are difficult to explain without invoking the nonadaptive forces of genetic drift and mutation. In addition, emergent biological features such as complexity, modularity, and evolvability, all of which are current targets of considerable speculation, may be nothing more than indirect by-products of processes operating at lower levels of organization.

Multicellularity is widely viewed as a unique attribute of eukaryotes, somehow made possible by the origin of a more complex cellular architecture and, without question, with the assistance of natural selection. However, it is difficult to defend this assertion in any formal way. Complex, multicellularity has only arisen twice, once in animals and once in vascular plants.  One might add fungi to the list, although the number of fungal cell types is not large, and there is some question as to whether multicellularity was ancestral to the phylogenetic group that contains animals, fungi, and slime molds. In any event, the probability that two or three origins of multicellularity simply arose by chance within eukaryotes as opposed to prokaryotes is somewhere on the order of 1/4 to 1/2, well below the general standards of statistical validity. Of course, many other eukaryotes are capable of producing a few different cell types, but the same is true for prokaryotes, some of which produce radically different cell morphologies.

Nevertheless, King (45) states that ‘‘this historical predisposition of eukaryotes to the unicellular lifestyle begs the question of what selective advantages might have been conferred by the transition to multicellularity;’’ and Jacob (46) argues that ‘‘it is natural selection that gives direction to changes, orients chance, and slowly, progressively produces more complex structures, new organs, and new species.’’ The vast majority of biologists almost certainly agree with such statements. But where is the direct supportive evidence for the assumption that complexity is rooted in adaptive processes? No existing observations support such a claim, and given the massive global dominance of unicellular species over multicellular eukaryotes, both in terms of species richness and numbers of individuals, if there is an advantage of organismal complexity, one can only marvel at the inability of natural selection to promote it. Multicellular species experience reduced population sizes, reduced recombination rates, and increased deleterious mutation rates, all of which diminish the efficiency of selection (13). It may be no coincidence that such species also have substantially higher extinction rates than do unicellular taxa (47, 48).

Because it deals with observations on historical outcomes, frequently in the face of incomplete information, the field of evolution attracts significantly more speculation than the average area of science. Nevertheless, a substantial body of well tested theory provides the basis for understanding the pathways that are open to evolutionary exploration in various populationgenetic contexts. Four of the major buzzwords in biology today are complexity, modularity, evolvability, and robustness, and it is often claimed that ill-defined mechanisms not previously appreciated by evolutionary biologists must be invoked to explain the existence of emergent properties that putatively enhance the long-term success of extant taxa. This stance is not very different from the intelligent-design philosophy of invoking unknown mechanisms to explain biodiversity. Although those who promote the concept of the adaptive evolution of the above features are by no means intelligent-design advocates, the burden of evidence for invoking an all-powerful guiding hand of natural selection should be no less stringent than one would demand of a creationist. If evolutionary science is to move forward, the standards of the field should be set no lower than in any other area of inquiry.

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7 responses to “The Frailty of Adaptive Hypotheses

  1. “Although those who promote the concept of the adaptive evolution of the above features are by no means intelligent-design advocates, the burden of evidence for invoking an all-powerful guiding hand of natural selection should be no less stringent than one would demand of a creationist. If evolutionary science is to move forward, the standards of the field should be set no lower than in any other area of inquiry.”

    Wow.

  2. Interesting paper.

    Lynch’s essay neatly encapsulates nearly everything that is wrong with Neo-Darwinian theory. Has Lynch let the cat out of the bag? Traditional population genetics theory, Neo-Darwinism, is not really a theory about adaptation! (Is it even a theory of evolution?!)

    I’m going to leap to the conclusion, as does Lynch: Because the forces of mutation, recombination, and genetic drift are now readily quantifiable in multiple species, there is no longer any justification for blindly launching suppositions about adaptive scenarios without an evaluation of the likelihood of nonadaptive alternatives. Moreover, if the conclusion that nonadaptive processes have played a central role in driving evolutionary patterns is correct, the origins of biological complexity should no longer be viewed as extraordinarily low-probability outcomes of unobservable adaptive challenges, but expected derivatives of the special population-genetic features of DNA-based genomes.

    Lynch has leaped to the conclusion that “the forces of mutation, recombination, and genetic drift are … nonadaptive alternatives… nonadaptive processes… “ Traditionally Neo-Darwinists have remained blithe in their ignorance of alternative theories of biological evolution in which mutation, recombination, and genetic drift are adaptive processes. I believe this ignorance is studied.

    But in conclusion Lynch attempts to extend an already failed paradigm, Neo-Darwinian theory, to include as positive evidence for Neo-Darwinism, results obtained quite independently and previously cited as supporting alternative theories.

    This kind of thing has been going on for a long time now. Can’t let ’em get away with. Its not so much a free lunch–its robbery!

  3. Sorry, Mike Gene, but Lynch kinda ticks me off.

    “Four of the major buzzwords in biology today are complexity, modularity, evolvability, and robustness, and it is often claimed that ill-defined mechanisms not previously appreciated by evolutionary biologists must be invoked to explain the existence of emergent properties that putatively enhance the long-term success of extant taxa. This stance is not very different from the intelligent-design philosophy of invoking unknown mechanisms to explain biodiversity. Although those who promote the concept of the adaptive evolution of the above features are by no means intelligent-design advocates…”

    Bullshit. The evolution of complexity, modularity, evolvability, and robustness are well-defined mechanisms and were not, and obviously still are not, completely understood (less appreciated) by Neo-Darwinian evolutionary biologists.

    The comparison to IDers is offensive. No offense intended IDers. I am sure you do not fail to appreciate what Lynch’s aspersions intend.

  4. Rock wrote: “Bullshit. The evolution of complexity, modularity, evolvability, and robustness are well-defined mechanisms….”

    I’m not sure but I think Lynch was saying that the mechanisms that supposedly led to complexity, modularity, evolvability and robustness are ill-defined. Therefore, if I understand Lynch, he’s putting neo-Darwinists on the same footing as us IDers.

  5. Sorry, Bilbo, but the mechanisms that lead to robustness, etc. are well-defined, intensely investigated, and understood, at least on some level, if not on the level of Neo-Darwinian theory.

    Neo-Darwinism is on the “same footing” as ID and other forms of creationism, because creationists have largely accepted Neo-Darwinian theory as their “working hypothesis” of biological evolution and as the near-perfect foil of creationism. That’s because, in many respects, at a basic conceptual level, Neo-Darwinian theory was designed to be the foil of creationism!

    E.g., evolution is a process of the pure coincidence of four (five? Or any number of) “forces” each operational independently of the others. Leading to common misconception of biological evolution as “extraordinarily low-probability outcomes.” The idea that evolution is too improbable to believe is purely the mathematical artifact of Neo-Darwinian theory.

    Bilbo, ID, per Dembski, says nothing about mechanisms. A non-starter.

  6. Hi Rock,

    I’m going to leap to the conclusion, as does Lynch: Because the forces of mutation, recombination, and genetic drift are now readily quantifiable in multiple species, there is no longer any justification for blindly launching suppositions about adaptive scenarios without an evaluation of the likelihood of nonadaptive alternatives.” Moreover, if the conclusion that nonadaptive processes have played a central role in driving evolutionary patterns is correct, the origins of biological complexity should no longer be viewed as extraordinarily low-probability outcomes of unobservable adaptive challenges, but expected derivatives of the special population-genetic features of DNA-based genomes.

    Welcome to the Rabbit Hole known as front-loading. Anyone who has paid attention to my mumblings for all these years knows I have never made a focus on extraordinarily low-probability outcomes a central focus of my approach. Quite the contrary.

    But in conclusion Lynch attempts to extend an already failed paradigm, Neo-Darwinian theory, to include as positive evidence for Neo-Darwinism, results obtained quite independently and previously cited as supporting alternative theories.
    This kind of thing has been going on for a long time now. Can’t let ‘em get away with. Its not so much a free lunch–its robbery!

    Well, as I write in my book, “The Duck causes us to see more ducks.” Or, the Duck absorbs all data.

    But I give Lynch great credit for exploring evolution without insisting that natural selection must sit on the throne. It’s a dangerous road for the non-teleologist, as natural selection is the designer-mimic needed to account for the appearance of design.

    BTW, Lynch’s thinking has clearly influenced Eugene Koonin. Anyone remember this one?

    However, I am afraid that, if our goal as evolutionary biologists is to avoid providing any grist for the ID mill, we should simply claim that Darwin, “in principle”, solved all the problems of the origin of biological complexity in his eye story, and only minor details remain to be filled in. Actually, I think the position of some ultra-darwinists is pretty close to that. However, I believe that this is totally counter-productive and such a notion is outright false.

    Emphasis added.

  7. I find this all quite amusing.

    I’ll defend IDers and think that they are partially responsible for the small revolution taking place today. They’ve pushed the short-falls of Darwinism out front even if you disagree with their theory. They rocked the Titanic and its sinking.

    As far as mechanisms being “well defined” today. I’m curious how that proves or disproves anything in the past.

    What are those mechanisms? HGT? What else?

    Exactly how does HGT create modularity? How does anything in evolution create modularity? Without teleology?

    Please enlighten me what else creates complexity of a motor that rotates at 20,000 rpm which none of our best engineers in the world can create at nano scale, if not some telic design process from the start?

    I find the notion of emergent, unguided mechanisms to be mind-numbingly absurd. Talk about a science stopper and fiction starter.

    I also find it highly suspect to point to some fictional role in the past or non-role, but just waiting to be used part. You cannot possibly prove the existence or evolution of such roles. It is still in the end speculation at best. Whether a protein exist for millions of years before it is utilized in a rotor mechanism that it happens to fit in optimally is still speculation.

    Just because wheels existed in charriots 2000 yrs ago, does not mean that they’re modular components that would one day turn up in gran prix cars zooming along at 200mph without a guiding intelligence. To extrapolate out such nonsense to the biological world is still based upon unguided Darwinian evolution. It is still playing by their rules.

    A Design inference at the very least gets the scientist-engineer looking for possible design patterns and techniques. We know how real world intelligent agents work. We know that within 2000 yrs, we are progressing towards miniturization of machine parts at nano-scale levels by intelligent research.

    No Darwinist ever proposed a “mechanism” that he did not first observe. HGT was observed first, not predicted. And HGT is fully a non-Darwinian mechanism. An unpredicted discovery that flattens Darwinist theology.

    For the record, I’m undecided on ID, FL, Creationism, etc., but at least pulling parts from the three sheds light on the obvious weakness of Darwinism.

    Isn’t low probabily a function of “unguided” processes? Am I wrong? I think that is the only obvious point to be made by Design theorist vs Unguided Theorist.

    FL avoids low probability through overall predictable and limited guidance. How does this differ from ID?

    Just because you do not argue for low probability does not mean FL is immune to the argument. FL improves probable outcomes via pre-ordained design techniques and algorithmic plottings for life’s diversity. It limits the search and helps adaptation.

    FL I think is an argument for high probability events given the same environmental circumstances against Darwinian models.

    If not, why not? Where am I going wrong?

    I agree that unguided evolution is to improbable to believe. But FL makes it much more probable. ID merely pointed out the flaws of Darwinian and neo-Darwinian theory. And so did Creationist.

    Are they to be scalped for such good critical thinking? I hardly think so.

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