The language of evolutionary biology and psychology is built on concepts applicable in the first instance to individual strategic rationality but extended to the level of genetic explanation. Current discussions of mental disorders as evolutionary adaptations would apply that extended language back to the individual level, with potentially problematic moral/political implications as well as possibilities of confusion. This paper focuses on one particularly problematic area: the explanation of women's greater tendency to depression. The suggestion that there are "good evolutionary reasons" for depression makes sense, and might be helpful to note in therapy, as implying that the tendency is not a defect. However, evolutionary adaptiveness should not be confused with individual or psychological adaptiveness. Besides making reference to an earlier environment, it presupposes a strategic standpoint that may not accord with the legitimate interests of the individual, as this example makes vivid.
Among the sources of confusion fostered by the language of adaptation in evolutionary biology is a tendency to talk in terms of strategies and reasons. In popular discourse, one often hears that there are "good evolutionary reasons" for some trait that might otherwise seem unhelpful or objectionable. As applied particularly to gender issues this normative language can seem to justify status quo expectations that arguably ought to be corrected, such as patterns of male dominance or the double standard.(2) In this paper I want to ask how it applies to women's tendency to depression.
The well-known prevalence of depression in women--accordubg to American Psychiatric Association (1994), p. 341, the lifetime risk of major depression is 10 to 25 percent for women, versus 5 to 12 percent for men--illustrates some of the general questions raised by applying evolutionary discourse to issues affecting human behavior and welfare. The bit of discourse featured in the title of this paper--the appeal to "good evolutionary reasons," with its normative or justificatory overtones--is more on the level of informal banter among proponents of evolutionary explanation than official terminology. But it highlights an important question, the question of the normative force of appeal to evolution. In any case, some of the official terminology ("adaptive" and related terms like "fitness") raises related problems. Avoiding natural misinterpretation takes constant vigilance--within the community of scientific experts, not just among outsiders--in ways that this example will make vivid.
That psychiatric classification ("nosology") has political implications (as well as sources) should be evident to anyone familiar with the recent debate resulting in removal of homosexuality from the list of disorders (Bayer, 1981). There is by now a huge theoretical literature within psychiatry about the nature of mental disorder and whether and how values should affect diagnostic categories (Sadler et al, 1994). I shall later try to cast some doubt on a recent recommendation by philosophers (Murphy and Stich, 2000, and Evans, unpublished) that neo-Darwinian theory be used to provide a more unified scientific basis for classification.
The community of psychiatric experts is not just a scientific community but also an institution, and its diagnostic categories serve some very practical purposes, most notably insurance purposes. However, this essay is not intended primarily as a contribution to the debate over psychiatric nosology. Rather, I am writing from the standpoint of moral philosophy--but not from a view that is antagonistic to uses of evolutionary theory. My concern is with the normative implications of evolutionary explanation. Though many of these are merely apparent, some are real. In both cases they may be worrisome from the standpoint of gender politics.
Neo-Darwinian evolutionary theory was built on the language of the mathematics of rational choice, or game theory, as applied in the first instance to individuals in situations of social conflict (see Von Neuman and Morgenstern, 1947; for the extension to evolution cf. esp. Axelrod and Hamilton, 1981, 1390-96, and Maynard Smith, 1982). Current evolutionary models extend this normative vocabulary to the genes, presumably an area where it will not mislead, or at any rate cannot do much harm--until it is read back onto the human sciences. My conclusion in what follows will be that at least some of the resulting confusion survives reasonable attempts at clarification. On the other hand, not all such normative talk is confused. I shall begin with this point since it is often not acknowledged by philosophers.
1. Defending Depression
Most moral or other philosophers dealing with normative issues would tend to dismiss talk of "evolutionary reasons" as really just talk of causes, with inappropriate normative overtones where behavior is in question. There is a standard distinction between justificatory and explanatory reasons that is relevant here (see Korsgaard, 1996, pp. 14-16). Evolution gives explanatory but not justificatory reasons--not reasons telling you that or why you should do something, or should have a certain tendency or trait, or be commended for having it. In other words, evolutionary reasons are not reasons in favor of anything but just serve to explain why it came to be.
I think this response is a bit overstated, however. Evolutionary reasons do not tell you what to do, but they might still provide a satisfying rationale for behavioral traits or tendencies from a certain standpoint--both genetic and historical--that may or may not be in line with the current or the appropriate standpoint of either the agent or society. This would not put evolved traits beyond criticism or complaint, but it would offer a partial justification for them--not just an excuse, though its force is ex post facto. It cites what might be called "defensive" reasons.
Consider depression, or particularly its prevalence in women, and suppose it does turn out to be an evolutionary
adaptation. I shall consider in a moment how such a claim might be fleshed out in theoretical detail; but in general, all it seems to mean is that the tendency to depression served to promote genetic survival in the environment in which it evolved. For most evolved traits the relevant environment is thought to be Pleistocene hunter-gatherer society, which is therefore sometimes referred to as the ancestral environment, or the environment of evolutionary adaptation, the EEA. I shall use the latter abbreviation in what follows.
It is of course another question whether depression is adaptive in contemporary life--particularly in the usual sense in which a psychiatrist or clinical psychologist would use the term "adaptive," referring to effects on the lives of individual patients rather than replication of their genes. Even if depression is adaptive in the evolutionary sense--indeed, even if it were so now, in the contemporary environment--it might still be thought of as a mental disorder, particularly in its more severe forms, in which it incapacitates the individual for the normal conduct of life. Even in milder forms it would at least seem to count as a symptom for which one might reasonably expect treatment or therapy.
Evolutionary biology and philosophy of biology following Robert Brandon (1990) have lately come to avoid normative implications by dropping the adjective "adaptive" in favor of the noun "adaptation" in reference to evolved traits. However, despite the possible confusions introduced by the standard terminology (which I shall exploit below), it is also important to recognize that attributing depression to "good evolutionary reasons" may have a normative or justificatory point--even one that could conceivably be helpful in therapy, by offsetting the reasons for self-blame that can often compound depression or keep it going. An implication of the evolutionary claim is that the tendency to depression is not in every sense a defect. From an evolutionary standpoint, it may be part of a good design strategy and in that sense not such a bad thing.
Of course, even with the complexities already noted, things are not so simple. The rationale that serves a therapeutic purpose in treatment of someone already suffering from depression might still be subject to criticism as a widespread social assumption. Outside the therapist's office, evolutionary backing for the prevalence of depression in women might just serve to enshrine the tendency as "normal" in women, along with other alleged components of women's special point of view.
Some philosophers and others in this area propose basing the classification of mental disorders on evolutionary psychology, but thinking about this example gives me pause. A psychiatrist or other mental health professional is supposed to be acting in the interests of individual patients rather than genes--or species or some other unit of natural selection. I want now to look a bit more closely at some of the basic issues of theoretical interpretation that I have indicated. Even if the evolutionary approach were to yield a neater or more principled system of classification than the one currently in use by psychiatrists, as these authors claim, confusion can be seen to creep in when we raise the question of standpoint: For whom, or what, are there good evolutionary reasons for depression?
2. Current Models
I should note, first, that an evolutionary account of mental disorders would not necessarily explain them as evolutionary adaptations.(3) That just seems to be the currently favored approach, at any rate to what the current U.S. psychiatric classificatory manual, DSM-IV, classifies as Major Depressive Disorder, involving moderate to severe episodes of depression; see American Psychiatric Association (1994), pp. 339-45. For Dysthymic Disorder, involving chronic but less severe depression, there is one theory in the field according to which the problem is faulty information processing: a tendency to overestimate one's own contribution to social groups relative to that of other participants (McGuire et al, 1994). The general response tendency this information feeds into, reciprocal altruism, still amounts to an adaptive mechanism, here as elsewhere. The dysthymic patient has "good evolutionary reasons" to be weighing his social contribution in comparison to that of others; but he apparently reads the signals wrong and feels exploited by others, without such good reason.
Even on the general sort of approach I mean to be considering, which tries to make out depression as somehow adaptive in evolutionary terms, the current work by philosophers cites two basic alternative accounts of how depression functions: as an inducement to change one's niche in social competition (the "social competition" model) or as backing up a threat to defect from social cooperation (the "defection" model).(4) After outlining and illustrating these two approaches I shall bring in a later combination view that is supposed to do a better job of explaining depression in women.
In a nutshell, the social competition model (Price et al, 1994) makes out depression as adaptive insofar as it gets the loser in a competition for evolutionary fitness to cut his losses and find some other "niche" in which he can win. However, the theory goes on to say, it is only in the small-group, face-to-face setting of the EEA that this reactive mechanism would work reliably. In the contemporary environment of global competition, we almost inevitably know of someone better in whatever niche we are in.
For instance, to apply the model for illustration to a familiar enough case from the recent self-help literature (Simon, 1993): a tendency to depression in reaction to perceived deficits in professional achievement is likely to undermine the efforts of a contemporary academic, an economist who is in a position to compare himself to colleagues worldwide.(5) But we might suppose that moving to a different territory out of the range of more successful hunters, as prompted by feelings of depression, did improve the situation of his ancestor in the EEA. On the social competition model feelings of depression were fitness-enhancing in the EEA insofar as they served as a barrier to further competition in situations where it would have been fruitless. As a result, though, many of us have inherited a predisposition to respond with such feelings to perceived competitive losses, even though in the contemporary environment the response is evoked too readily to be helpful.
The suggestion that it was helpful at an earlier stage needs extended clarification, some of which I have already noted. Depression need never have been helpful to any given individual for this account to work. The claim is just that the costs it imposed on an individual promoted the survival of his genes.
However, this, too, really needs a gloss, since genes themselves do not survive but rather copies of them. For that matter, "copies" need not mean genes in some way derived from them, but merely further instances of the same type: genes for a certain tendency or trait, in this case depression.(6) What the individual is said to get for himself here is "fitness"--"reproductive fitness"; or a better term is "inclusive fitness," since the notion extends to genes passed on through cousins and siblings and the like rather than just one's own offspring.
One common objection to the social competition model of depression is that it seems to be tailored to the situation of male competition in the EEA. By contrast, the defection model (Hagen, 1999) particularly fits postpartum depression, the depression women sometimes experience after childbirth. On this alternative account, depression functions as psychological backing for a threat to defect from social cooperation (here specifically child care) unless one gets a higher level of support from the social environment.
The point of depression is to impose involuntary costs on the individual so that unless others come to her aid she will not be able to function adequately and will have to move on--not to another "niche," as on the social competition model, but to other offspring. Note that these include potential offspring, those the mother would have in better circumstances later if she invested less in the current offspring; they need not be offspring she in fact has or ever will have if this one survives.
The point needs underlining, since it is natural to suppose that a mechanism promoting the survival of offspring would reinforce the tendency toward maternal care. The point of postpartum depression is rather to counteract the latter tendency by incapacitating the mother emotionally as a way of demanding social support.
The two models are obviously not unrelated, and one could see how they might be combined, or how they might work together in application to a single case. The evolutionary explanation each model gives for depression seems to fit a different gender's role in the EEA, but in the contemporary environment they would apply naturally enough across the sexes to different kinds of situations that can trigger depression: suffering competitive losses, on the one hand; and on the other hand (in some cases), doing particularly well. The situation of postpartum depression might be said to be like that of someone who reacts with depression to a long-awaited achievement--an academic who has just published a book, say, to vary Simon's (1993) case.
The defection model gives an evolutionary explanation for the tendency to depression in terms of social bargaining for support rather than individual competition. We might imagine that the depressed economist in our variant case inherited his depressive tendencies from a female ancestor in the EEA for whom depression functioned as a way of demanding support from her offspring's father or other genetic kin.
Note that this is not to say that depression serves a similar social function in the contemporary environment--though that might be a possibility worth exploring in some cases. Its evolutionary history presumably would have an effect, however, on what circumstances trigger depression, both in general and in a particular individual. Perhaps in the variant case of the depressed economist (the figurative postpartum case) depression might be explained as a reaction to lack of sufficient social acclaim for achievement in an environment in which one's main support comes from the competition.
At any rate, the circumstantial element is important as the source of confirming evidence for an evolutionary account, which otherwise is often charged with providing only a "just-so" story for the way things in fact turn out. Hagen (1999) cites detailed experimental evidence that the defection model does fit the circumstances of postpartum depression (meant literally) even in the contemporary environment.
What the social competition and the defection models have in common, to make a long story short (bypassing many areas of possible criticism, as well as interest), is the explanation of depression as a kind of emotional self-handicapping strategy for achieving longer-term gains.(7) Again, much qualification is needed about just who stands to "gain" and in what sense something involuntary can be called a "strategy." We also need to keep reminding ourselves that the strategy is limited (as far as the theory goes) to the EEA.
In any case, the defection model apparently has problems of its own in explaining the general prevalence of depression in women. Though it fits a situation that might be thought typical of women in the EEA, its focus is narrower than women generally, or women in the contemporary environment, which of course is where the higher rate of depression is found.
There is a more recent variant of the model (Watson and Andrews, 1999) that attempts to do better on the issue of women's depression. This is called the "niche-change" model, and it effectively subsumes both of the two models discussed so far by interpreting depression as a goad to effecting change in a social niche that is mismatched to the individual's capabilities. Mismatched niches include both competitions that an individual is not likely to win by persistent efforts and cooperative arrangements such as child care that she is not likely to be able to renegotiate by active bargaining.
The prevalence of depression in women even apart from childbirth gets explained on this model by barriers to the effectiveness of more active moves on their part to induce change. Depression amounts to a passive strategy of becoming unable to take care of oneself in a social environment in which others' fitness depends on one's own--a kind of involuntary "labor strike," as on the defection model. By escalating from minor into major despression if others do not respond with support, it essentially "extorts" support from the group. But the relative paucity of small, face-to-face groups in modern society--a point that was stressed previously on the social competition model--here implies that the tendency to escalate will nowadays mainly make things worse.
As to why this particularly affects women, the detailed explanation offered by the niche change model turns on two alleged features of women's positions in groups: patrilocal society (the situation thought to be standard in the EEA, where the female in a pair-bond joins a group not related to her by kinship and thus less likely than her own kin to provide unilateral support) and the nonhierarchical patterns of cooperation among females (which is said to make the groups they form less responsive to active bargaining for support).
Note that the second feature is also typical of the contemporary environment. One might attempt to fill out the account with other barriers to actively inducing change in the contemporary environment that stem from patterns of relations between the sexes. However, the niche-change model on its current version suggests a genetic factor to explain why contemporary women exhibit major depression in greater numbers: There is evidence of a slower rate of serotonin processing in women (Heninger, 1997, and Nishizawa et al, 1997) that may strengthen the tendency of depression to escalate when support is not forthcoming.
So now let us consider a female version of the depressed economist. The implication of the niche-change model is that women inherit the predisposition to depression in greater numbers.(8) In a competitive contemporary environment such as academic life, where individuals also positively affect each others' fitness by their competitive achievements (by way of departmental reputation and the like), incapacitating oneself for competition is unlikely to generate social support, so that feelings of depression in response to some minor setback would tend to escalate, without limit or strategic point.
3. Adaptive Disorders?
Just for purposes of argument in what follows, to keep things relatively simple, let us suppose we accept the niche-change model or some similar account of the evolutionary function of depression. We can then say that in the relevant sense there are "good evolutionary reasons" for the high incidence of depression in women.
It would be natural to take this as suggesting that depression amounts to a kind of unconscious coping strategy--if not now, then in the EEA; and if not on the individual's own behalf, then on behalf of the species or her genes. It increases women's "fitness" in their peculiar social niche. However, even to the extent that women's social circumstances now still reflect those in the EEA, the argument would imply only that depression increases women's fitness generally, or on average, not that it does so in any particular case.
Even in general terms, moreover, we need to be wary of the suggestion that depression serves as a beneficial personal strategy, perhaps one that in the short-term involves self-sacrifice, in the form of dedication to the welfare of one's (collective) offspring or other genetic kin. This form of psychological endorsement--as often conveyed by psychological uses of the term "adaptive"--does not really follow from the normative claim I allowed for earlier: that an evolutionary account serves to justify the tendency to depression, at least in a defensive sense, as not simply a defect but rather a product of good evolutionary design. It is only from some standpoint other than that of the person that an adaptive tendency in the evolutionary sense can be seen as beneficial.
Let us take another example of something debilitating to the individual that might be adaptive in an evolutionary sense: aging. At least some of the symptoms of age that we expect a doctor to treat or to prevent when possible--for that matter, also death--might be held to have an evolutionary function insofar as they encourage reallocation of scarce resources to more viable kin. They might sometimes even have the same function in the contemporary environment--promoting "fitness" in the genetic or evolutionary sense, in contrast with the usual medical or health-related sense. But in response to "good evolutionary reasons" of this sort, it is always open to the individual to respond: "What's evolution to me?"
A process like aging that is designed to benefit species or genes at the cost of the individual organism would seem to involve "dysfunction" in an evolutionary sense only in relation to an intermediate level of organization at which the relevant evolved mechanism is assumed to operate. For instance, in a case of heart disease associated with aging, a particular organ of the body, the heart, can be said to fail in fulfilling the function for which it evolved. The analogy for depression would be that of functionally distinct mental mechanisms, or "modules."
What counts as functional at the various levels we might distinguish--that of the organism, of particular organs or modules, and of the organism's store of genes; or more generally, of evolutionary design--can sometimes conflict. However, a psychiatrist or other mental health practitioner is supposed to be particularly concerned with the level of individual functioning--with social/behavioral dysfunctions such as an inability to sustain relationships or to satisfy the demands of a job. "Dysfunction" in an evolutionary sense might not always fit such cases, since the aims of evolution sometimes pull against those of the individual.
Consider mental slowdown associated with aging. Any organ or mental mechanism or module we can identify here may indeed be fulfilling its evolutionary function in a full sense that includes an element of "planned obsolescence": to undermine this organism at a certain stage in favor of its genetic kin. By the same token, evolutionary arguments for the adaptiveness of depression should not be taken as indicating that it is adaptive in a psychological sense--the sense that would naturally occur to psychiatrists and others thinking about mental disorders. Even if depression were still adaptive in the contemporary environment in something like the evolutionary sense, whether it any way aids the individual organism is a distinct question.
This distinction needs to be kept clear, since there is an overlap in the sorts of arguments that would support evolutionary versus psychological adaptiveness. For instance, current evolutionary models stress the usefulness of depression in registering defects in the social niche and motivating the individual to change it accordingly. This might be developed into an argument for the psychological adaptiveness of depression, but the result would be a different argument from the one given in support of depression as an evolutionary adaptation.
I think we should be wary, then, of suggestions that the classification of mental disorders might be based on evolutionary criteria. My objections apply, albeit in different form, even to standard psychiatric definitions such as Wakefield (1992) that appeal to evolutionary dysfunction as a necessary condition of disorder. If depression should indeed turn out according to the best evolutionary arguments to have been adaptive in the EEA, that would be poor reason in practical terms for removing it from the list of mental disorders.
Murphy and Stich (2000) following McGuire and Troisi (1998) substitute for evolutionary dysfunction a necessary condition of mismatch with the contemporary environment, allowing for disorders that might have been adaptive in the EEA but are not so now--but on the other hand ruling out psychopathy or antisocial personality as disorders in current social environments where they still (at least arguably) are adaptive now. However, we need to keep clearly in mind that, even when the focus shifts to the contemporary environment, it is evolutionary adaptiveness that is in question here--effectiveness in getting one's genes into the gene pool rather than (necessarily) in promoting one's own interests.
The general approach appeals to a notion of biological function, or "proper" function (cf. Millikan, 1989, and Neander, 1991), that would seem to provide a relatively neat starting point for classification, particularly in comparison with the complexities of DSM-IV. However, one should not expect too much neatness after that point. Besides changes in the environment, an adequate theory would need to accommodate the change in standpoint from the subpersonal level of genes to the level of individual organisms choosing personal goals--in accordance with an older, Aristotelian notion of human function, which is still quite alive as a normative practical ideal. It is here that the use of normative (as well as purposive) terms from rational choice theory--"gain," "benefit," "strategy," and the like--threatens most to mislead.
It is likely to mislead practitioners too--even practitioners of theoretical science--and not just a general audience. The neo-Darwinian approach already has to explain away many of the terms it applies to species or genes, but presumably insiders are unconfused by the extension. Darwinian psychiatry would seem to switch standpoints back again, to the personal level, where the terms came from.
The resulting confusion has ideological implications on issues affecting women. "Fitness" in the relevant sense is often given a brief gloss as "survival or reproduction," but the biological situation of women illustrates how these aims can come apart. With respect to depression, current evolutionary models might serve to reinforce features of women's social situation that already exert pressure toward accepting a low hierarchical status, possibly in exchange for social support.
Depression can indeed signal important information about the social environment that ought to be explored rather than simply medicated away or dismissed as cognitively irrational. But one should not forget that a strategy of emotional self-handicap results in a handicap. Sometimes depression may be a response to a situation that calls for protest, of a sort that would be undermined by the advice to find a more supportive "niche" somewhere else or to remain in place and accept the situation, including the tendency to weaken oneself emotionally as a way of attracting support.
Appeal to "good evolutionary reasons" for mental disorders such as depression does have a valid normative point, and one that might be useful in therapeutic contexts, as I have argued. It implies that some conditions that we think of as mental disorders are not really defects--from the standpoint of human development via genetic propogation in the EEA. However, one ought to be cautious about inferring from this that they therefore are not disorders. Even where they can also be shown to be adaptive in the evolutionary sense here and now, that still leaves room for wide divergence between an individual's best interest and that of her gene pool--as illustrated by applying evolutionary accounts to the case of depression in women.
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1. I owe thanks, for conversation on this topic, to Karen Neander. An early draft of the paper was presented at a conference on evolutionary psychiatry of the New York City chapter of the Association for the Advancement of Philosophy and Psychiatry in November, 1999, with Paul Watson as keynote speaker. I received very useful comments from William Bechtel, Edward Hagen, Dominic Murphy, Jennifer Radden, John Sadler, Ben Scofield, Kathleen Wallace, David Wasserman, and an anonymous reviewer for Philosophical Psychology.
2. I am relying here on conversational sources, but for a sample of early discussions of gender issues and evolution in the conservative political terms associated with "sociobiology" see esp. Wilson (1978), pp. 121-48. Later authors try to be more careful about ideological implications; cf., e.g., Wright (1994), for a more liberal view. For a recent contribution to the controversy in this general area see Thornhill and Palmer (2000).
3. For general objections to adaptationist explanations in evolutionary biology see, e.g., Gould and Vrba (1982).
4. My twofold classification is based on Murphy and Stich (2000) with the first category interpreted as covering views like Nesse and Williams (1994) that make out depression on the model of pain, as a signal to the organism to cease some costly activity. Typically, though not necessarily, the "cost" in question is social.
5. I should note that Simon's own description of this case (which is autobiographical) is framed in terms of a cognitive-behavioral approach, without reference to the evolutionary explanations I apply to it speculatively in what follows.
6. This general point is worth stressing in connection with applications of evolutionary game-theoretical reasoning to moral philosophy; see esp. Skyrms (1996). Even if justice, say, as the tendency to make fair deals, can be shown to increase its numbers in a given population, one has to ask in what sense that would amount to the triumph of the just. (I do not mean to suggest that Skyrms intends this reading of his argument, which also famously shows that unjust and/or irrational strategies have a place in a stable strategic mix.) Early practitioners of justice who "take over" a population in a sense that just involves numerical increase (without reference to genetic relationship, let alone power) would be rewarded thereby only on the assumption that their aims include an impersonal regard for justice.
7. For discussion of emotions generally as evolutionary self-handicapping strategies cf. Frank (1988); cf. my extension of the argument to individual rationality in Greenspan (2000).
8. It occurs to me to note in passing that depression does not seem to be more common among women than among men in academic life. No doubt a woman exhibiting symptoms of major depression would be more likely to be "killed off" early by competition, unless she moves to a noncompetitive niche within the relevant hierarchy. In any case, the niche-change model claims only to explain the comparative statistics for women versus men overall. However, the explanation offered by the model seems to cover only differences in major depression (or at any rate, relatively severe depression), insofar as it turns on the tendency of minor depression to escalate. But if sex differences extend beyond this--to the tendency, say, to react with minor depression to minor setbacks--then without further argument it is not clear how the niche-change model can claim to give a better explanation of them. The real explanatory work on this issue seems to be done by the appeal to differences in serotonin processing, which in principle is open to any of these accounts (among others).