Adaptationism and Its Criticism - Evolutionary Explanations of Behaviour

3. Evolutionary Explanations of Behaviour

3.1. Adaptationism and Its Criticism

For Charles Darwin (1859), there were two major features in nature that needed an explanation that the evolutionary theory could pro-vide: the family-like similarities between species (or unity of type), and the fact that biological beings seem to be designed for their environ-ment. The first question is answered by common ancestry and the sta-bility of certain developmental and structural features from genera-tion to generagenera-tion (phylogenetic inertia), and the second one by the mechanism of natural selection. (See Depew & Weber 1996; Gould 2002.) Evolutionary explanations are historical explanations for why certain traits exist in the population and why they possess certain gen-eral characteristics. Natural selection explanations are evolutionary explanations that refer to natural selection as the primary explanatory factor, in contrast to, for example, drift, or developmental constraints.⁴⁷

47 Developmental constraints are the factors in the individual development that limit evolutionary change either by limiting the range of phenotypic variants that are possible in the ontogeny (generative constraints) or by limiting the viability or

The developmental constraints both conserve the developmental forms from earlier evolutionary history (resulting in homological simi-larities and partly explaining phylogenetic inertia) and bias the direc-tion evoludirec-tionary change by constraining the producdirec-tion of variadirec-tion for selection to work on (see Maynard Smith et al 1985; Amundson 1994 & 2001; Richardson & Chipman 2003; Pearce 2011). There are also random factors that affect evolution, such as drift and mutation. Since they are not directed, their effect gets smaller over time, but they do have consequences, especially on small populations (Futuyma 1998).

Moreover, adaptation takes time and is path dependent. Natural se-lection explanations are not the only evolutionary explanations. In what follows, I will give a very brief review of some of the critical dis-cussion on adaptationism. My intention is not to participate in this discussion as such. The clarification of various possible adaptationist stances and their criticism is a starting point for developing my own account of evolutionary functionalism in explanation and helps to clarify what I am proposing.

3.1.1. Kinds of Adaptation Explanations

In the previous chapter, I defined natural selection, following Endler (1986), as a process in which:

C1) there is variation in the given phenotypic trait on the popu-lation level,

C2) there is a consistent relationship between the trait and fitness, and C3) the trait is inherited, and because of this,

O) there will be a change in the frequency of distribution of the variation in the trait between generations.

survivability of the organism during ontogeny (including through the consequences for other developing traits; selective constraints) (Richardson & Chipman 2003).

C1–C3 constitute an explanatory mechanism for O. Note, however, that the condition C2 only states that there is a consistent relationship between the trait and fitness, or, that the expected reproduction rate relative to others in the population. It does not specify why the rela-tionship holds. To establish this, we need to specify a mechanism link-ing the trait and fitness. A causal (non-arbitrary) connection could hold because the trait

C2a) is adapted to its environment (that is, it has benefits for the survival of the individual possessing it in that specific en-vironment),

C2b) enhances the individual’s reproductive capacity (fertil-ity, mating success, and so on),

C2c) has a supportive function for another trait that fulfils C2a or C2b directly, or

C2d) is otherwise associated with another such trait (for exam-ple, because of a structural or developmental connection such as pleiotropy).

C2a–c are cases of the trait itself causally contributing to the fitness and therefore its own existence. They are selected for instead of just being selected, as in C2d (see Sober 1984a). Being adapted (C2a) is a qualitative ecological notion that refers to the fit between the organ-ism or its trait and its environment (Brandon 1978). An organorgan-ism can be more or less adapted (and in many cases variation can be quanti-fied, and one can make optimality models for measurement), but the notion is about the qualitative fit, having a function, in contrast to the quantitative notion of fitness. Fitness is a measure for reproduction capacity of an entity that reproduces: depending on what the theory in use allows, a gene, an individual, or a group. The fitness of an indi-vidual (or a gene) supervenes on the indiindi-vidual’s traits (or the traits associated with the gene) depending on their overall adaptedness (C2s) as well as the factors in C2b and C2c. Fitness is not a causal

property itself: it is a measurement of relative differences between re-productive units in the causally relevant properties that direct evolu-tion by natural selecevolu-tion. (Futuyma 1998; Sober 1984a: 97–102). What is usually meant by “adaptation” is either the process in which a trait evolves because it gets selected for its adaptedness, or the trait pro-duced by this process. The adaptation explanations rely not only on the mechanism of natural selection (which covers all C2s) but also pre-suppose that the trait has something it has been selected for, its adap-tive function. In the strictest interpretation only C2a qualifies as an ad-aptation since it is the only one in which the adaptive value of the trait is causally related to its origins. In a more inclusive reading, explana-tions referring to C2b or C2c can also be included in the adaptation explanation, although they may have originated for some other adap-tive purpose or for none at all, and have only acquired a new role.

Stephen Jay Gould and Elisabeth Vrba (1982), for example, distinguish true adaptations from such traits, which they call exaptations. I will ar-gue later why a more inclusive reading is more sensible. Traits that are selected because of an association (C2d) but have no selective func-tion are by-products.

Not all evolutionary explanations are adaptation explanations:

some are by-product explanations, some refer to drift or phylogenetic inertia, and some may refer to historical contingencies in the evolu-tionary pathways. “Evoluevolu-tionary explanation” is a larger category,

“adaptation explanation” is a sub-category. Adaptations and natural selection have, however, a central place in evolutionary explanations.

In what follows next, I will highlight the reasons why and under what limitations. I will also discuss the explanatory relevance of adaptive functionality extracted from a mere causal-historical explanation.

Evolutionary adaptation explanations are interested in history, but a snapshot of the current adaptation process may be interesting in some cases, too. Moreover, as I mentioned in my discussion on mechanisms, an explanatory causal structure (such as the factors constituting a nat-ural selection) may exist without a causal process going through it.

More importantly, there is another reason besides the explanatory

relevance for why we think that C2a is special among the C2s: it is related to how the organism fits its environment. I will argue that this is in itself an important perspective for understanding living beings, not just because of its role in evolutionary-historical explanations.

3.1.2. The Problems of Adaptationism

The methodology of studying practically all biological traits as adap-tations, or presupposing they are adapadap-tations, was labelled “adapta-tionism” by Stephen Jay Gould and Richard Lewontin (1979) who be-gan to criticize it as a flawed practice (see also Gould & Vrba 1982;

Gould 2002; Lewens 2009). Adaptationism is, however, several things wrapped into one package. I will now distinguish different concepts of adaptationism. This is not done to sort out different views – in fact, the “adaptationisms” discussed next are not different stances or views about adaptation, and they are not theoretically independent either.

The aim is, instead, to sort out the overall baggage of adaptationism that is a net of connected ideas about the nature of biological evolu-tion, explanatory choices, and methodological tools. The purpose of this is to find out how evolutionary explanations could and should be understood in the context of social behaviour and what the conse-quences of this are for the issue of individualism vs holism in the hu-man context. A starting point for distinguishing between various ideas related to it is Peter Godfrey-Smith’s (2001) distinction between empirical, explanatory, and methodological adaptationism, that can be further refined into several alternative interpretations of the subject matter; I will mostly follow Tim Lewens (2009) in this. Furthermore, a fourth important aspect of adaptationism (that was also discussed in Gould & Lewontin 1979) is the issue of atomism and holism⁴⁸ about the characteristics of an individual: how isolated from the overall

48 “Holism” as in the holistic nature of an individual organism, in contrast to an individual being a mosaic of traits that perform their evolutionary func-tions in isolation from each other.

architecture of the organism and its behaviour can we presuppose the traits under explanation to be in their adaptive function?

Some of these forms of adaptationism or distinct contents of ad-aptation claims can be distinguished into further sub-categories. The forms of adaptationism that I will discuss are the following, with some preliminary characterizations:

Empirical adaptationism - all traits are products of adaptation⁴⁹ Pan-selectionism - natural selection overrides other forces Good-designism - the overall design of organisms is a

good fit to the environment

Well-enough-designism - the overall design is functional in the environment

Gradualism - the evolution of a trait is about a grad-ual change

Explanatory adaptationism - the replies to evolutionary questions in-clude a reference to natural selection Strong historical expl. adaptationism - in evolutionary history, explanatory

questions will have an adaptation an-swer

Weak historical expl. adaptationism - in evolutionary history, explanatory questions will have an answer that in-cludes natural selection

Ahistorical expl. adaptationism - adaptive functions are explanatory for the functioning of the organism

49 This may be more or less inclusive in what counts as “adaptation”, as dis-cussed above. The definition has implications for what adaptationism in this sense means, but we can disregard this for the current discussion.

Methodological adaptationism - all traits should be treated as if they were adaptations

Historical meth. adaptationism - traits should be treated as if they were historically selected for what they do Ahistorical meth. adaptationism - instrumentalistic adaptationism in the

functional description of the organism

Atomism - traits are treated in isolation of each other regarding adaptivity

Empirical adaptationism is a claim about nature and its history, about the causal factors guiding the evolutionary history. According to it, everything (or almost everything) in nature serves an adaptive pur-pose and has been selected for that. In other words, it is an empirical claim about the relative powers of natural selection and other factors in evolution, and it is connected to actual historical processes.

Whether or not this is so is a part of the research object of evolutionary biology proper, and from that perspective, this is the main question.

Furthermore, it is the idea that most criticism of adaptationism has been targeted against.

There are two sets of possible alternative factors for natural selec-tion to be actual historical reasons for a trait to exist (see Gould &

Lewontin 1979; Futuyma 1998). The first set consists of chance events.

Since both populations and the time that they have to adapt to a par-ticular environment are finite, the right mutations may or may not ap-pear. Furthermore, there is a chance element in the order of mutations appearing, which may be consequential, and natural selection is path-dependent in any case. Drift and migration may have consequences depending on the relative strengths of these factors and the selection.

The other set of factors comes from the holistic nature of organisms and their development that constrains natural selection (see also Amundson 1994 & 2001; Gould 2002). There are structural dependen-cies between functionally different parts of an organism, the

developmental processes may connect both functionally and structur-ally separate traits, and some path-dependencies in the development make some changes in the organism’s design impossible. Empirical adaptationism is in its essence an empirical thesis about the strength of natural selection in relation to these factors. This in turn contains a whole set of presuppositions. Tim Lewens (2009), for example, further distinguishes three conceptually distinct presuppositions within em-pirical adaptationism: pan-selectionism, good-designism, and gradualism.

Pan-selectionism is the empirical adaptationist claim about the strength of natural selection in relation to the chance factors: natural selection is the strongest causal factor acting on the population level.

The development does not matter, since this is a thesis about what happens to the variation that is available in the first place.⁵⁰ A comple-mentary empirically adaptationist claim would be precisely about the strength of natural selection over developmental factors. This claim would say that natural selection can break the links between function-ally different traits and overcome all possible developmental con-straints. This position is probably embraced by no one, since it is simply an absurd claim from a biological point of view. But there is a weaker version of it, which Lewens calls good-designism. According to this idea, organisms are overall well adapted to their environment, even if many of their characteristics are not produced by natural selection for the purpose to which they are being put. I will return to this idea later in more detail. Pan-selectionism and good-designism do not entail each other. The third form of empirical adaptationism that Lewens discusses is gradualism, a claim that all apparent design in the nature is produced by gradual evolution guided by natural selection for the particular purpose that they are designed for. This rules out things like

50 Developmental constraints (see Amundson 1994 & 2001) are, of course, con-straining possibilities for the evolutionary process, but natural selection does not produce variation but rather selects from it, so this should not be thought to constrain natural selection as such (Orzack & Sober 1994a, 1994b & 1996;

Sober 1998b). Developmental constraints are constraints for evolution, but not for natural selection.

an evolved trait adopting a new function (or, to use a term proposed by Gould & Vrba 1982, becoming an “exaptation”). Gradualism is inde-pendent of the other two forms of empirical adaptationism.

The problem with all three claims of empirical adaptationism is that they are empirically false.⁵¹ There are other population-level fac-tors than natural selection, organisms are not always optimal for their environments or in their design – biology is full of bad design rooted in structural and developmental constraints⁵² – and traits often adopt new functions (see Futuyma 1998). But it is important to keep these complications separate and distinct even in non-adaptationist meth-odological considerations about the role of adaptation explanations and adaptive functionality, and I will return to them in the next sec-tion. At the same time, even many of the most ardent critics of adap-tationism think that natural selection is, in some sense, the most im-portant factor in evolution (see Gould & Lewontin 1979; Gould & Vrba 1982; Gould 2002). The point is not that adaptationist explanations are invalid or unimportant, or that true adaptations would be rare, or an-ything like this. The point is that there are other factors that should be taken into account, the developmental factors being the most im-portant. One of the main targets of criticisms in Gould and Lewontin’s original anti-adaptationist paper was that sometimes some

51 See Futuyma 2010 for a review of empirical adaptation “failures” and some of the known and speculated reasons for this.

52 For example, there are vestigial parts and structures that have lost their us-age and have become burdensome. An often-used example of this, because of its striking dysfunctionality, is the anatomy of giraffe’s neck. First, there are developmental constraints that limit the number of neck vertebrae that seem to be specific for mammals but not, for example, for birds. Almost all mam-mals (with the exception of sloths) have only seven cervical vertebrae, which makes their necks unnecessarily vulnerable from a purely design point of view. Second, their recurrent laryngeal nerve makes a long, unnecessary loop that is dysfunctional. (Badlangana, Adams & Manger 2009.) Traits like this call for an evolutionary explanation that describes the non-adaptive contin-gencies of the actual evolutionary history.

evolutionary biologists simply presuppose the traits under study to be adaptations, and if a hypothesis fails, another adapatationist hy-pothesis is made, while the correct explanation for the trait’s existence is not an adaptationist one in nearly all cases.⁵³ This cannot be ac-cepted, of course: even if a trait being an adaptation for something is a primary hypothesis in studying its evolution, the fact of it really be-ing so should be a result of evaluatbe-ing evidence, not a presupposition guiding the interpretation of empirical data. This is simply lazy and methodologically bad science.

3.1.3. Adaptationism as an Explanatory Perspective

Abandoning crude empirical adaptationism, there are still other pos-sible justifications for granting adaptation and adaptive functionality a special role in research, from an explanatory or methodological point of view. Some proponents of adaptationistic approaches highlight the uniqueness of natural selection as an explanatory resource, because it is the only thing that can account for adaptive complexity (Dawkins 1983

& 1986; Dennett 1995; Sober 1998). Traits could be adaptive by chance, and evolving systems tend to become more complex over time, but the only known factor that guides the evolving complexity systemati-cally towards adaptive organization is natural selection. According to some, this gives adaptationist explanations a kind of priority: natural selection is not the only causally contributing factor, but it is the dif-ference-maker for the questions in which we are interested most in evolutionary biology. This is the view Godfrey-Smith (2001) calls

53 In practice, if there are several possible evolutionary hypotheses, only ad-aptationist ones are generated or taken seriously, or adaptivity itself is con-sidered evidence for the hypothesis. Elisabeth Lloyd (2006) provides a reveal-ing case study on this practice. She points out that the existreveal-ing evidence seems to back a by-product hypothesis on the evolution of human female orgasm, while the various adaptationist hypotheses are almost exclusively discussed in the literature.

explanatory adaptationism, and as he remarks, it is more charitable to consider many adaptationists explanatory rather than empirical ad-aptationists (and this would probably include Richard Dawkins 1983

& 1986 and Daniel Dennett 1995). I will later make a further distinction between historical and ahistorical explanatory adaptationism.

As mentioned above, much of the criticism from Gould and his collaborators is aimed at the presupposition that, from a causal-his-torical point of view, some adaptationist explanation is going to be cor-rect. This strong version of historical explanatory adaptationism would be the thesis that all adaptedness to the environment is in fact selected for and it would presuppose (all forms of) empirical adapta-tionism. A weaker version would be a view that acknowledges other factors but gives adaptation a special status: even though there are multiple causal factors in the evolutionary past, natural selection has an explanatory priority. As Godfrey-Smith (2001) and Lewens (2009) point out, the formulations that fall under this view (for example, Dawkins 1986) often sound like statements of what is interesting (ver-sus boring) as an explanatory question, or what is the “proper” object of study within the discipline. This makes the question something of a matter of taste and an unnecessary normative constraint on research

In document Evolving in Groups : Individualism and Holism in Evolutionary Explanation of Human Social Behaviour (sivua 91-109)