Evolution

Six Sayings About Adaptationism

Elliot Sober (full reference coming shortly)

This article sets out the discussion of adaptationism as a universal evolutionary law analogous to Newtonian physics as a framework for investigating various points of contention within the evolutionary discipline. If the analogy is true, then barring the intrusions of other possible forces, natural selection will always favour the fittest trait(s); thus the effects of other forces can be relegated to the status of unimportant because, most of the time, natural selection will achieve or mostly achieve its goal. Some of the issues in regards to this topic that are addressed are: the role of exaptations, the significance of developmental constraints, and the testability of adaptationist stories.

(Page 72) “In a population subject to natural selection, fitter traits become more common and less fit traits become more rare, unless some other force prevents this from happening…resulting phenotype is said to be optimal, not in the best conceivable trait, but in the sense that it is the best of the traits available.” I am worried here about the criteria for optimal. It seems to me that underlying these parameters are value judgments about the persistence of life. In other words, optimal is optimal because it contributes to the sustenance of life, so the persistence of life is the greatest locus of value. Why is this so and does this value actually contribute, detract from or is neutral to life cycles? Is death not also important?

(Pg 74) “Saying number 1: ‘Natural selection is the only natural process that can produce adaptive complexity.”

Criticism: Certain things like waterfalls and crystals also display a complexity yet we would not classify them as products of natural selection.

Response: But they are not evolved, in terms of decent and modification. Did they thus evolve via another process? But what other process of evolution is there? At some point, evolution must have been a set of chemical reactions…which is what crystals are, and what waterfalls are, in a much broader extension of that of course, so why the differentiation of evolutionary processes? A trait is not adaptive until it is present is all members of a population and benefits survival or fitness. How then do we describe things, be it traits or behaviors, that are present in all members of a population but deter fitness? I am thinking of things like addiction, for example. Or poor rational abilities. I admit that it is difficult to think of any trait that is truly ubiquitous. Regardless of these criticism, the author suggests that adaptationism concerns the pervasiveness and power of natural selection, thus is a tool to not be readily dispensed with.

(Pg 75) “Saying 2: ‘Adaptationism is incompatible with the existence of traits that initially evolve for one adaptive reason but then evolve to take over a new adaptive function.’”

Criticism: some people label something as an “adaptation” when is merely a co-option of an adaptation for something else. In other words, the trait is merely a by-product of the development of a different trait.

Response: Yes this is true, it may be some form of secondary adaptation but it is still adaptation none the less and should not be cause for a disruption in the adaptationist program over all. This response seems a little weak to me in that it seems like it would be difficult to be anywhere near certain about the adaptation story, thus, aside from a pure aesthetic value (which I do not necessarily dismiss), what is the value?

(Page 76) “Saying number 3: ‘Adaptationism is incompatible with the existence and importance of constraints that limit the power of natural selection.’”

Criticism: If adaptation is to Natural Selection like is like a bowling ball is to gravity in the Newton analogy, the law of reproduction of the fittest will always prevail. Thus, other forces are too minute to be of much consequence. If adaptation is more like a feather, then other forces that may interfere are important. The criticism is that there are other forces, constraints, that are very important, thus the adaptation program is seriously flawed.

Response: Constraints might well be an aspect of adaptationism achieving fitness. It is not clear if constraints are actually separate and distinct forces. Thus this criticism is not sufficient for abandoning adaptationism.

(Pg 80) “Saying number 4: ‘Adaptationism is untestable; it involves the uncritical formulation of Just So Stories.’”

Criticism: Well adaptations are subject to stories. These stories are a bit dynamic, and are only replaced with other stories if some portion does not fit the evidence.

Response: Individual stories are easily testable and falsifiable; however, more generally, it is difficult to prove that the no true story could possible exist. Well biologists have just not found a good way to test yet, as long as stories are based on strong evidence, the pursuit of better testing is a viable goal. I find this problematic, and a bit of a cop-out. Surely there could be a better answer than this. But I have to think about it more before I can come up with a good criticism of this response.

(Pg 82) “Saying number 5: ‘Populations of organisms are always finite, always experience mutation, and frequently experience migration and assortative mating. Optimality models fail to represent these non-selective factors and therefore are false.’”

Criticism: Optimality models are unrealistic because they cannot represent all the forces at play in population.

Response: True, but they come close. Because they are generally monistic, their breadth is not all that it could be. Pluralistic models are better but it really all comes down to the data: the better the data the better the model and predictability….and plural models are typically better. Whatever.

(Pg 83) “ Saying number 6: ‘Adaptationist thinking is an indispensable research tool. The only way to find out whether an organism is imperfectly adapted is to describe what it would be like if it were perfectly adapted.’”

Criticism: there is none, the author agrees.

Again, I would like to know how one knows what the criteria of optimality are. Does one have to play ‘god’ so to speak? Hypothetically, if each organism could reach the optimal…wouldn’t this diminish diversity?