evolutionary psychology

On the subject of objections to Buller's book, I should point out that Buller himself has a website where he has additional work and some responses to critics (particularly this reply to the short comments in TiCS).

Also on the subject, does anybody else think this debate is looking very much like the crocodile vs. python deathmatch from last week?

Chapter 4 of David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature is a critique of the concept of massive modularity applied to the human mind. To me, this chapter is weaker than chapter 3, on adaptation, not because the critique is necessarily wrong but because the examples are less compelling.

The idea of massive modularity is that the brain has domain-specific processing circuits for a very large set of mental tasks that humans perform. According to evolutionary psychology, these circuits are the adaptations to past environments that allowed ancient humans to make adaptive decisions and pursue adaptive behaviors. Many EP proponents assert that there may be hundreds, or even thousands of such modules (hence, "massive" modularity).

The differentiated brain circuits set these "domain-specific" modules apart from the hypothesis of "domain-general" intelligence, in which most mental tasks are performed by a single flexible mechanism. Thus the difference between massive modularity and domain-general intelligence is one of mechanism: in the first case, there are different circuits dedicated to different tasks; in the second, there is a single immense circuit that accomplishes a multiplicity of tasks.

Buller sets out to attack the hypothesis of massive modularity on four bases:

1. Humans don't have enough genes to build hundreds or thousands of cognitive modules.

2. Neural development in the brain is complex and self-organizing on the basis of environmental inputs: they are environmentally shaped, not genetically specified.

3. Well-defined sensory "modules" in the brain have extensive cross-modal communication, making it doubtful that less-well-understood and subtler cognitive modules could be functionally separate in any meaningful way.

4. A domain-general mechanism, given appropriate innate information (such as which kinds of stimuli are important to attend to) can do anything that separate cognitive modules can do.

Of this list, I think that the fourth is most important, and the fairest:

The point is ... that Cosmides and Tooby fail to show that domain-general mechanisms can't generate domain-specific solutions because their arguments rely on a misrepresentation of how a domain-general problem-solver would function in different problem domains. Consequently, the crucial step in the argument for massive modularity is unsupported, so we're given no reason to believe that the mind can't be a general-purpose problem solver" (Buller 2005:146).

Buller applies the analogy of antibodies as a domain-general system: the immune system does not have a genetic specification for every antibody; they are built from a simple generalized assembly mechanism that adapts to different pathogens as necessary. Likewise, the brain builds its neural structures in response to environmental conditions in a way that can adapt effectively to them.

But although Buller argues that the brain might function in this way, he provides little evidence that it does do so. And that is where the weaknesses in his evidence seem plain.

The number of human genes is simply irrelevant. Clearly writing the book a few years ago, Buller claims that we have only 30,000 to 70,000 genes. It is now clear that the number is closer to 20,000. But this is no argument against the idea that the brain has a complex genetic design; any more than it can argue against the idea that the body has a complex genetic design, as it clearly does. We simply don't know how complex a structure can be built from any given number of genes. But we can make a guess. The operation of developmental and regulatory genes depends on the joint expression of multiple genes, each of which may form different overlapping expression gradients. Small numbers of genes expressed in different concentrations in different tissues lead to differentiation -- a cascade of signals causing genes to turn on or off and resulting in different structural elements. These combinations of genes are thus combinatorial in their effect, not additive. Thus, 20,000 genes can build structures that are arbitrarily complex.

But could this have all happened during the short span of human evolution? Again, we have no idea what limits there may have been on evolutionary change in human brains. But consider that the development of structures in the brain takes very long compared to some aspects of development. The basic architecture of the body -- the limbs, number of verbebral segments, differentiation of tissue types, origins of internal organs and sensory organs -- all happens over the course off a few weeks in early embryos. In contrast, the migration of neural cells to different parts of the cortex, the formation of functional brain circuits, and the biochemical basis of normal adult cognition take several years. The migration of cells, the ease of forming new connections or severing old ones, the likelihood of neuron pruning or cell death, and the differentiation of circuits all depend on gene expression. This gene expression must vary among brain regions -- if it did not, then different brain functions such as vision, language learning, motor coordination, and others could not become effective at different times in ontogeny. There clearly are developmental windows and differences in developmental rates for some brain functions. What is not known is how extensive such ontogenetic structuring may be. But there is no reason to think that massive modularity couldn't have evolved during human evolution.

Neural plasticity is certainly extensive. Buller does not mention some of the most profound examples, such as regaining function after brain damage and even hemispherectomy. But plasticity does not preclude the genetic specification of some neural functions. And two distinct pieces of evidence argue in favor of a strong genetic role. First, there are distinct functional areas of the neocortex. The most well-known (and defined) are the language areas, such as Broca's and Wernicke's areas. Indeed, Buller even sets language aside completely, as a "specially complex" case where modularity may be important to neural function. But language is not the only function that involved particular brain regions. And there are differences in the brain regions involved in certain functions between males and females. This kind of sexual dimorphism does not point to purely environmental causation for cognitive structure; it reflects the influence of genetic switches (like those discussed by Buller in chapter 3) on later brain development.

The second evidence in favor of some genetic specification for human brains is the fact that other kinds of primates cannot be trained to do many human cognitive tasks. Now, Buller could argue (he does not) that the brain has some kind of gatekeeper function, that enables humans to make better or more effective use of cultural stimuli, and thereby renders humans different from chimpanzees and other apes despite being similarly domain-general in cognitive processing. I'm not sure that I wouldn't argue this myself -- although I would be hard-pressed to explain why such "gatekeeper" functions would not themselves be human-specific cognitive modules.

The key point is that human cognition is not free of some genetic influences. It is therefore not implausible that human brains could have evolved semi-discrete modular circuits to accomplish specific, fitness-related tasks. Indeed, if there were strong selection in favor of some behavior or decision, humans would conceivably be much better off being able to adapt by evolving dedicated circuits to conduct the behavior or make the decision rapidly and accurately.

If there is a theoretical objection, it must be framed in terms that explain why selection would not lead to such functional specificity. I can't think of any reason why it should not be possible in priniciple to evolve massive modularity. Partly this is because human brains are quite modular -- we have different cognitive circuits to handle different sensory inputs, perception, emotion, sleep, and so on. Some of these greatly overlap in their area and function, but it is not accurate to say that such functions are accomplished by domain-general intelligence. My own opinion is that human cognition is domain-general because such a process works better with cultural systems of knowledge. But demonstrating this requires empirical understanding of human cognition, not arguments about gene number and brain construction.

The Wason selection test

For this reason, Buller's critique of the empirical evidence for modularity is the better part of the chapter. The critique of the Wason selection test is the majority and the strongest part. There are lots of reasons why these tests don't necessarily yield the proposed information about human mental structures; Buller strikes upon several of these.

Throughout the book, Buller is concerned with the relation of theoretical grounding and empirical evidence. The recurring point is that evolutionary psychology claims a theoretical grounding from evolutionary theory for their hypotheses, and that EP also claims strong empirical evidence. For Buller, it is not enough to challenge the empirical studies, because one might easily argue that although some particular experiment may be flawed, the theory is still compelling. So he is at pains to detail why both the theory and the evidence are weak.

Buller's argument (on pages 171 and 172) relating to the Wason tests as evidence for a cheater detection module begins with a theoretical point. He notes the origin of the problem of cheater detection in Trivers' work, which outlined the necessary conditions for reciprocal altruism to evolve. Reciprocal altruism is a social exchange, in which two actors both collaborate in conditions that give both actors a benefit and exact from both actors a cost. But the Wason selection tasks used by evolutionary psychologists do not involve social exchange, but instead social contracts, in which one actor is obligated to perform some action (i.e. a cost) in order to obtain a benefit.

There is, therefore, a disconnect between the theoretical support for the cheater-detection module and the empirical results that purportedly provide evidence of its existence. The theory behind the cheater-detection module should lead us to expect a mechanism that is specialized in detecting chaters in the domain of social exchanges. But the experimental results that purportedly support the existence of a cheater-detection module involve detecting cheaters in the domain of social contracts. ... [A]lthough we have a well-developed theoretical understanding of how social exchanges evolved, we have no comparable theoretical understanding of how social contracts evolved (and Evolutionary Psychologists offer no theory about the evolution of social contracts) (Buller 2005:172).

It is fair to ask what the difference between social exchange and social contracts really is, since they clearly are similar to each other. Buller does not explain this well, so one may be tempted to read his argument as mere semanticism. But there is a key difference: a social contract can involve any combination of cost and benefit to the individual. The punishment may fit the crime, as it were, or it may not: the rules are the same either way. It is this breadth that allows evolutionary psychologists to design situations that are "culturally distant" from their research subjects -- they can claim that cassava root is a great aphrodisiac and that sexually active men must have tattoos, and the rules are the rules, period.

In contrast, a social exchange is vastly narrower: as modeled by Trivers and applied to human evolution, a social exchange is one in which the benefits to each individual must outweigh the individual's cost. Only a comparatively limited set of interactions can fit this criterion, which was Trivers' point concerning reciprocal altruism. As a system, such exchange may be a subset of social contracts, but human society gives rise to many kinds of contracts that cannot validly be considered as examples of social exchange. The rules governing such contracts are imposed from above by society. Buller does not make this explicit, but it seems evident that a "module" for enforcing social contracts need have little logically in common with a "module" for conducting reciprocal exchange. His point is that there is no theory to account for the former, while the empirical data do not fit the latter.

Deontic conditionals

After this theoretical point, Buller embarks on an explanation for the observed Wason selection test results that does not involve specialized cognitive modules. The first aspect of this is the apparent "content effect" in the tests: people "get the right answers" more often when the task involves social contracts than when the task involves abstract numbers, or even social situations that do not involve contracts.

It seems to me that anyone who takes Chomskian generative grammar seriously must recognize the possibility that two sentences with apparently similar surface forms "if P then Q" might well have different deep structures. Fodor and Buller assert that exactly this is the case: that the indicative conditionals take the form of scientific propositions ("If you eat duiker meat, then you have found ostrich eggshell"), whereas the social contract deontic conditionals take the form of obligations ("You cannot eat cassava root if you do not have the tattoo"). We should be no more surprised at a person interpreting these two sentences in different ways than we would be at a person interpreting many aspects of language.

Of course, another way of problematizing the Wason selection test results is to notice the extremely poor performance of most people on the arbitrary "indicatively conditional" relations. The problem would not be to explain why people do well on the social contract problems, but why instead they do poorly on the abstract problems. According to evolutionary psychology, it is because people are not adapted to solve these abstract problems.

According to Buller, the poor performance on arbitrary problems is due to a lack of sufficient information.

Indicative conditionals that embody arbitray connections between antecedent and consequent conditions, and that are presented within very sketchy and artificial background stories, do not appear with a sufficient number of the informational properteies on which subjects normally rely in representing the logical type of a conditional utterance (Buller 2005:180).

Buller discusses experiments that confirm this view, in which people perform better with more information. I can confirm this myself; as I have used the Wason test on classes to illustrate it, students do better once they understand how the test works, practice being another way of providing background.

But there is another possibility that Buller does not raise, but is discussed by Jonathan Lowe in his An introduction to the philosophy of mind. When people are presented with arbitrary information and asked to generalize it, a perfectly valid approach is inductive reasoning. The Wason selection test assumes that a deductive approach is the correct one. But deductive logic in the face of unfamiliar data can be silly:

Consider, by way of analogy, how a scientist might attempt to confirm or falsify a general empirical hypothesis, such as the hypothesis that if a bird is a member of the crow family, then it is black. Clearly, he would do well to examine crows to see if they are black .... But it would be foolish of him to examine non-black things, just on the off-chance that he might happen upon one which is a crow and thereby falsify the hypothesis (Lowe 2000:198).

According to this view, the central issue is one of practical reasoning. In practice, it combines with the lack of background information: most people use deductive reasoning only with reference to well-understood problems that they have much experience with. This is why Sherlock Holmes stories continue to be entertaining; he uses deductive reasoning in situations where most people would not. But people can hardly be faulted for using practical inductive reasoning in a situation where deduction has not been keyed by background information.

More on Adapting Minds

References:

Buller DJ. 2005. Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. Bradford Books, New York. Amazon

Lowe EJ. 2000. An introduction to the philosophy of mind. Cambridge University Press, Cambridge UK.

I'm reading through David Buller's Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. It's a back-burner read for me; I pick it up when it's time for the twins to nap. Still, it is hard to put it down in the middle of a chapter.

The book is a critique of evolutionary psychology as practiced now, and an attempt to redirect the field to a better evolutionary grounding. I should mention that throughout Buller refers to "evolutionary psychology as commonly practiced now" as "Evolutionary Psychology" with a big "EP". This is because he has the ambition of establishing an "evolutionary psychology" with a little "ep" by purging all the flaws of the present form. I find this very irritating myself; I would rather he just have come up with another name, just as the "Evolutionary Psychologists" came up with that to replace "sociobiology". So I will try to avoid this confusion by never referring to the field as it "should" be, but only as it exists.

In any event, Buller has an admirable thesis. Unlike other critics, especially Stephen Jay Gould, Buller does not believe that evolutionary psychology has a fatal flaw. Nor does he look for one; he is basically sympathetic with the aims and scope of evolutionary psychology. Instead, Buller thinks that almost every one of the substantive claims of evolutionary psychology are wrong, and that the problems lie in the details of these arguments. So he sets out to deal EP the death of a thousand cuts: outline the major empirical claims of evolutionary psychologists, and explain one-by-one why they are wrong.

That's not to say that Buller himself is right about everything. I'll probably write about my problems with chapter 4 ("Modularity") before long.

But chapter 3 ("Adaptation") is downright inspiring as an example of cut-to-the-bone evolutionary criticism. This chapter is the first real substantive criticism, following an explication of the goals and project of evolutionary psychology as it exists today.

This criticism begins by problematizing the concept of the "environment of evolutionary adaptedness" (EEA). There is little new here; although a specification of such an environment would be desirable in terms of identifying the adaptive problems faced by prehistoric people, there is no reason to suppose that Pleistocene humans faced environments that were spatially or temporally consistent enough to allow such specification.

Constructing adaptive problems

To me, the first significant point Buller presents concerns the "grain" of adaptive problems --- essentially the extent to which a problem must be described in terms of specific subtasks that an organism must perform. Here is his description:

As Tooby and Cosmides would argue, we can be quite confident that Pleistocene humans would have had to "select mates of high reproductive value" and to "induce potential mates to choose them," for example.

But here we encounter a problem concerning the "grain" at which these adaptive problems are described. It is true that we can always be certain that just about all sexually reproducing species face the adaptive problems of selecting mates of high reproductive value and inducing potential mates to become actual mates. These descriptions of adaptive problems are so course-grained, however, as to be wholly uninformative about the selection pressures that act on a species. Consider, for example, what one need do to attract a mate. Male bowerbirds must build ornately decorated bowers, male hangingflies must offer captured prey as a nuptial gift, and male sedge warblers must sing a wider repertoire of songs than other males. The adaptive problem of attracting a mate thus takes very different forms depending on the species... (Buller 2005: 97).

Buller goes on to describe the subtasks involved in such adaptations as consequences of species-typical psychologies. The main argument here is that we have no a priori knowledge about the adaptive problems faced by early humans, without taking into consideration substantial assumptions about their psychology.

For the anthropologist, a closely analogous problem is the hunting-vs-scavenging debate for early Homo. We can imagine the adaptive context of Late Pliocene environments including packets of meat on the hoof and packets of carrion at various stages of consumption by carnivores and scavengers. We can imagine the adaptive challenges of tracking and killing animals on the one hand, and of fighting off lions and hyenas on the other. But whether humans hunted or scavenged depends not only on these paleoecological considerations but also on human psychology itself. Humans do not hunt only for digestive satisfaction; they also do so for social prestige. This is not a recent development. Indeed the most widely-held hypothesis for the development of meat-eating (whether hunted or scavenged) is that males began providing meat as a way to provision females or dependent offspring. If the origin of meat-eating itself lies in social change, then the psychology of the first meat-eaters is an essential part of the adaptive context in which meat-eating arose. An assumption of optimal foraging may easily be wrong if the hominids are optimizing their social benefits rather than their acquisition of calories -- a distinction that becomes even more important for later hominids who hunt prime-age animals instead of the sick and weak.

Buller cites a passage from Richard Lewontin, which rings true for hominids when hominids and marrow-bones are substituted for thrushes and snails:

Indeed, the morphology and psychology of a species determine which aspects of the environment are adaptive relevant to the species. As the biologist Richard Lewontin says: "The bark of the trees is part of the environment of a woodpecker, but the sontes lying at the base of the tree, even though physically present, are not. On the other hand, thrushes that break snail shells include the stones, but exclude the tree from their environment. If breaking snail shells is a 'problem' to which the use of a stone anvil is a thrush's 'solution,' it is because thrushes have evolved into snail-eating birds, whereas woodpeckers have not. The breaking of snails is a problem created by the thrushes, not a transcendental problem that existed before the evolution of the Turdidae." (Buller 2005:98, citing Lewontin 1983:76)

After this Buller turns to the consideration of the evolution of social intelligence within a changing social environment, niche construction, and other reasons to think that the adaptive problems faced by prehistoric humans were far from stable, but instead were constantly changing. In this part, he makes an important point: that "adaptive problems" don't force a solution. Populations do just fine without solving adaptive problems, even if a solution might increase their adaptation by causing them to spread at the expense of other populations. The point is, that even if we could identify the adaptive problems faced by Pleistocene humans, we would have no reason to think they evolved adaptations to deal with those problems. The adoption of sign language might solve some adaptive problems for wild chimpanzees, but that doesn' t mean that the behavior necessarily will arise, nor that the fate of chimpanzees particularly hinges on it.

And there is this Gouldian passage:

Since selection builds solutions to adaptive problems by retaining modifications to preexisting structures, the form of a solution -- an adaptation -- will always be a function of the possible ways in which the preexisting structure could be modified. Consequently, we can never infer the structure of an evolved solution to an adaptive problem from the nature or the problem itself. We also need to know something about the preexisting structure that was recruited and modified to solve the problem. But, as argued previously, we simply don't know what kinds of preexisting psychological characteristics our ancestors possessed (Buller 2005:104).

The point of the section is that we cannot assume any a priori knowledge about past adaptive problems at all. We must begin with a substantial knowledge of our psychology in the first place. So the idea that we can infer psychological adaptations merely because of the adaptive problems that "must have" occupied our ancestors is fallacious. Buller argues that if we claim that humans have psychological adaptations, we must do so on the basis of human psychology as we observe it, not on the basis of presumed past adaptive problems.

Building complex adaptations

The other reason evolutionary psychology proposes for the necessity of considering the EEA is the idea that designing human psychological adaptations would require a lot of time. If this assertion were true, it would imply that humans are adapted to Pleistocene life but not more recent environments -- there just would not have been enough time for people to develop adaptations to recent environmental changes, like the development of agriculture and complex societies.

But this assertion is simply false, because as Buller points out it makes the false assumption that new psychological adaptations must be designed from scratch whenever the environment changes. If we instead imagine that selection need only modify existing adaptations, then there is no need to imagine that humans are still adapted to Pleistocene conditions. There has been plenty of time for selection to exert marked changes on human populations, as exemplified by the evolution of lactase persistence in some populations and the evolution of malarial resistance in others. Indeed, the recently selected alleles at the ASPM and Microcephalin loci may reflect changing psychological adaptations over a recent time span.

The psychic unity of humankind

By far my favorite part of the chapter is Buller's dismantling of the idea that human psychology must be universal. The idea of evolutionary psychologists has been that human psychology is so complex that it must involve many genes. According to this logic, different adaptive strategies in different people would require the inheritance of many different alleles at many different loci. Sexual reproduction with recombination makes the coinheritance of particular combinations of alleles at different loci very unlikely. Thus, complex psychological adaptations could not be polymorphic in human populations, and human psychology must therefore be universal.

Buller begins by noting that this argument would make sex itself impossible. Sexually dimorphic characters depend on a complex set of genes. But the expression and regulation of these genes is accomplished by a single genetic switch (the SRY gene) which is inherited as a single allele. Thus, the existence of such genetic switches provides an alternative explanation for the occurrence of multiple psychological strategies in a population.

Tooby and Cosmides hope to forestall this line of ragument, however, on the grounds that genetic switches are very rare in nature. They argue that selection consistently favors adaptive plasticity over polymorphic genetic switches as a method of producing adaptive differences (Buller 2005:116).

To shut down this argument, Buller again turns to sex. In mammals, sex is a genetic switch. In crocodiles, it is determined by incubation temperature. Some fishes alter sex in accordance with the prevailing sex ratio. There is no reason to think that any one of these methods is generally preferred in nature; each addressed adaptive proboems in the ancestors of the extant groups. Buller notes that frequency-dependent selection is just as effective on simple genetic switches as adaptive plasticity could be, even in principle.

On the other hand,

...there are some circumstances to which systems of adaptive plasticity are better adapted than genetic switches. In particular, when the environment is rapidly changing and unpredictable, the flexibility provided by phenotypic plasticity will clearly be a greater asset to an organism than a genetic switch. That is, if the environmental features being adapted to are highly variable from one generation to another, so that the phenotype determined by a particular form of a genetic switch would be effective at some times but not others, then phenotypic plasticity, which can produce phenotypes that are adaptive in each of hte variant environments, will clearly be more effective than a genetic switch (Buller 2005:118, emphasis in original).

The conclusion is that sometimes adaptive plasticity may be adaptive, and other times genetic switches may be adaptive, and there is no general rule. This means that there is no reason to believe that the evolved aspects of human psychology should be invariant or universal.

At the end of the chapter Buller engages in a reductio ad absurdum concerning "developmental programs". The "developmental program" has been proposed as the form of the "universal" aspects of human psychology. Since humans clearly have psychological differences, the developmental program is proposed as a set of if-then rules that construct minds in accordance with environmental inputs.

The essence of Buller's argument is that at least some of the time, some ancient human groups must have faced novel environments in which the developmental program had no preexisting instructions to create adaptive psychological mechanisms. Even so, many such people must have survived and managed to develop in adaptive ways. But if some people managed to adapt effectively to novel environments, there is no reason to think that all people couldn't have done so. This obviates the need for a universal "developmental program" entirely: if humans just have brains that are able to develop in adaptive ways in different environments, this solves the problem without the need for an additional level of specification:

But if adaptive phenotypes can develop in some environments without the need for a rule, they can develop in all environments without the need for a rule. This means that the notion of a set of rules embodied in a developmental program guiding development is idle; it plays no genuine role in explaining how development occurs. When we develop differently, it is not because something that is the same in us simply responds differently in a programmed way to differences outside us (Buller 2005:125, emphasis in original).

More on Adapting Minds

References:

Buller DJ. 2005. Adapting Minds : Evolutionary Psychology and the Persistent Quest for Human Nature. Bradford Books, New York. Amazon

Lewontin RC. 1983. The organism as the subject and object of evolution. Scientia 118:65-82.