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How the Mind Works is a synthesis of cognitive science and evolutionary biology that aims to explain the human mind with three ideas:
1. Computation: thinking and feeling consist of information-processing in the brain;
2. Specialization: the mind is not a single entity, but a complex system of parts designed to solve different problems;
3. Evolution: as with the organs of the body, our complex mental faculties have biological functions ultimately related to survival and reproduction.
The book lays out criteria for attributing an evolutionary function to a trait, and applies them to many hypotheses using data from cognitive science, psychology, anthropology, and biology.
In their review, Jeremy Ahouse and Robert Berwick dismiss it entirely. "Don't believe a word of it," they say about what they take to be its key assumptions. "More is not always more . . . it is sometimes disastrously less." Despite their vehemence, it is not easy to see what the substantive disagreement is about. Some scientists disagree with 1., and assert that the mind is a direct product of the biochemistry of the brain, but Berwick cannot be among them: he himself takes a computational approach to language and mind.1 Others disagree with 2., and assert that there is a generic neural network learning algorithm which the brain uses for every mental process. But Berwick cannot be among them, either: he works in a Chomskyan framework in which language is treated as a specialized module, and presumably he does not believe that language is the brain's onlyspecialized module. As for 3., evolution, Berwick cannot be opposed in principle to examining the phylogenetic basis of mental faculties, since he himself has recently done just that for language.2
There remains an issue of which mental processes are functional adaptations, as opposed to by-products of adaptations or the result of chance. It is unlikely that Ahouse and Berwick would deny that one can ever say that some part of the mind is an adaptation; the idea that stereo vision, fear, and sexual desire are adaptations to see in depth, avoid danger, and beget children are as indispensible and uncontroversial as the idea that the heart is an adaptation to pump blood or the kidneys are adaptations to filter it. There may be disagreements over whetherparticular mental faculties (such as probabilistic reasoning, grief, or humor) are adaptations, and if so, what they are for, but such arguments do not appear in Ahouse and Berwick's review.
The review becomes a bit less mysterious when we recognize that their accusations are taken, often wording and all, from Richard Lewontin. The review is the latest example of a conventional genre in modern intellectual life: the all-out attack by Lewontin or his collaborators (including Steven Rose, Stephen Jay Gould, and Philip Kitcher) on attempts to connect psychology with standard evolutionary biology. Since 1975, when Lewontin and others published their "Against Sociobiology" manifesto claiming that such attempts were politically reactionary and encouraged eugenics and Nazism, the attacks have recycled the same accusations and tactics: fuzzy scare words ("atomism," "reductionism," "determinism"), misreportings and doctored quotations, shameless straw-manning, empty name-calling ("vulgar," "pop"), political smears, personal innuendo, and most of all, the scientific snow job: seemingly damaging technical findings that general readers are unlikely to know about and hence unlikely to recognize as red herrings.3
How the Mind Works (HTMW) tried to preempt this kind of attack by patiently raising and refuting all the standard criticisms, both political and scientific. But Ahouse and Berwick (hereafter A&B) seem determined to discredit the book by any means necessary, and so rather than engaging its arguments, they have redoubled the use of shoddy tactics. As an example of their standards of fairness, here is an excerpt in which they try to show that I am ignorant of basic evolutionary biology:
Pinker asks, "Why don't women give virgin birth?" Certainly the correct answer will not make particular reference to humans. Mammals, including humans, just do not have this as a developmental option. Put otherwise, it would take more than just a shift in selection regimes to make humans start reproducing asexually. For these reasons it is hollow bluster to talk about the selective advantage of sex in humans if the traits we are discussing evolved and became established long before the human lineage branched.
This guy Pinker sure does sound naive! Unfortunately for the readers of Boston Review, the "hollow bluster" is a sentence fragment that A&B chopped out of context:
Why is there sex to begin with? . . . Biologically speaking, the costs are damnable indeed, so why do almost all complex organisms reproduce sexually? Why don't women give virgin birth to daughters who are clones of themselves instead of wasting half their pregnancies on sons who lack the machinery to make grandchildren and are nothing but sperm donors? Why do people and other organisms swap out half their genes for the genes of another member of the species, generating variety in their offspring for variety's sake? (pp. 461-62).
The discussion that follows also makes it clear that sex is puzzle for all organisms; humans are presented just as an example.
This is not the first time that Berwick has been caught doctoring a quotation in these pages; he also did it in his dismissive review of Richard Dawkins's fine book Climbing Mount Improbable.4 Nor is it the last time. As we shall see, A&B repeatedly fabricate the content of HTMW and misinform their readers about the technical results they marshal to criticize it.
Distortion 1: I uncritically believe that all traits are adaptations.
Let's compare the accusations with what I wrote:
A&B: "In evolutionary terms, every trait we examine is an admixture of physical constraints, natural selection and chance with history. These features are constitutive, not optional. Pinker presents a mutually exclusive conception pitting these factors against each other."
HTMW: "Natural selection should not be pitted against developmental, genetic, or phylogenetic constraints, as if the more important one of them is, the less important the others are" (p. 169). "Organisms can be understood only as interactions among adaptations, by-products of adaptations, and noise" (p. 174).
A&B: "All traits do not lead to a selective advantage, the origin of traits and their maintenance do not demand the same selectionist account. Pinker never embraces this distinction as a vivid part of his adaptationism."
HTMW on all traits leading to selective advantage: "The mind is an adaptation designed by natural selection, but that does not mean that everything we think, feel, and do is biologically adaptive (p. 23)." "The major faculties of the mind . . . show the handiwork of selection. That does not mean that every aspect of the mind is adaptive" (p. 174). "Some readers may be surprised to learn that after seven chapters of reverse-engineering the major parts of the mind, I will conclude by arguing that some of the activities we consider most profound are nonadaptive by-products" (p. 525).
HTMW on origin versus maintenance: "Many organs that we see today have maintained their original function. . . . Others changed their function. . . . [Sometimes] before an organ was selected to assume its current form, it was adapted for something else" (p. 170).
Distortion 2: I am an atomist and a genetic reductionist, reducing every behavior to a simple trait, and then, in a straight line, to a single gene.
This is exactly backwards. Behavior reduced to a single trait?
[The generator of behavior is] the package of information-processing and goal-pursuing mechanisms called the mind.[ . . . ]Any particular deed done today is the effect of dozens of causes. Behavior is the outcome of an internal struggle among many mental modules, and it is played out on the chessboard of opportunities and constraints defined by other people's behavior. (p. 42)
The on-board computers of social organisms, especially of humans, should run sophisticated programs that assess the opportunities and risks at hand and compete or cooperate accordingly. (p. 429)
Behavioral traits reduced to single genes?
The organization of our mental modules comes from our genetic program, but that does not mean that there is a gene for every trait (p. 23).
An emphasis on innate design should not, by the way, be confused with the search for "a gene for" this or that mental organ. [ . . . ]Complex mental organs, like complex physical organs, surely are built by complex genetic recipes, with many genes cooperating in as yet unfathomable ways (pp. 34-35).
Neither adultery nor any other behavior can be in our genes (p. 42).
A&B's specific charges are equally backwards. They charge, "A behavior like 'incest avoidance' gets boiled down to a simple heritable trait." I wrote the opposite: "Incest avoidance showcases the complicated software engineering behind our emotions for other people" (p. 456). A particularly blatant caricature comes in an attempt to educate us on birth order:
Birth order is a clear example of environment, not inheritance, as a prime mover (later-born children could not be expected on average to receive more gullibility genes from their parents). With the wind of adaptationism filling his sails, Pinker must claim that the whole behavioral repertoire response [sic] of first-borns or the inverse behavior of later-borns is all selected for.
Must claim? Here is what I do claim:
[Children] should calculate how to make the best of the hand that nature dealt them and of the dynamics of the poker game they were born into. The historian Frank Sulloway has argued that the elusive nongenetic component of personality is a set of strategies to compete with siblings for parental investment, and that is why children in the same family are so different. Each child develops in a different family ecology and forms a different plan for getting out of childhood alive. (p. 453)
All children being equipped with strategies for competing with siblings is very different from parents' directing gullibility genes to later-borns.
Oddly enough, A&B write as if they themselves believe that genetic atomism and determinism are required by the theory of evolution:
If genes are to serve as accurate bookkeeping chits for maximizing fitness, all the way to love's blushes, then the dotted lines from genes to behaviorsmust run straight and true. Any deviation, any non-determinism or interaction between and among the stepping-stones, and our explanatory hold slips .[emphasis added] (p. 38)
Again, must? It is a commonplace of evolutionary biology that genes are selected because of their probabilistic effects: a gene "for" a trait is a gene that, in comparison with rival alleles, and averaged over environments and over the other genes it appears with, increases the probability that the trait will appear. As A&B acknowledge later in the review, "Biologists have long said a lot about evolution without any detailed knowledge of the steps from genotype to phenotype. All you need are statistical correlations to move from gene to phenotype without a full causal story." Indeed they have. But A&B have just refuted their own claim that "the dotted lines from gene to behavior must run straight and true"!
Distortion 3: HTMW is just story-telling, and presents no basis for evaluating its hypotheses about the biological function of mental faculties.
A&B: Pinker knows that we can always replace one adaptive story by another or add more useful modules as required, but offers us no way to reasonably refrain from doing so.
In fact I "know" no such thing, do "offer us" a way, and do "refrain from doing so" myself.
First, I present standard criteria in biology for evaluating hypotheses about adaptive function. Obviously such criteria must exist. As Ernst Mayr, one of the century's seminal evolutionary biologists, has noted, "The adaptationist question, 'What is the function of a given structure or organ?' has been for centuries the basis of every advance in physiology. If it had not been for the adaptationist program, we probably would still not yet know the functions of thymus, spleen, pituitary, and pineal. Harvey's question 'Why are there valves in the veins?' was a major stepping stone in his discovery of the circulation of blood."
I detail these criteria right from the first chapter (pp. 36-40; also 155-74, 524-26). A good adaptationist explanation specifies a goal relevant to survival or reproduction, the causal structure of the organism's environment, and the engineering designs suited to attain that goal in that environment. It then requires empirical data showing that the trait in question uncannily meets the engineering specs, showing signs of complexity, effectiveness, and specialization in solving the assigned problem, especially in comparison with alternative designs that are biologically possible for that kind of organism.
These criteria are applied throughout. Frequent comparisons with other primates and mammals show that alternatives to what we find in humans, such as lacking language, living in solitude, or mating indiscriminately, are developmentally possible (thus A&B's logical possibility in which genetic variation for such traits is "meager" can be dismissed). And HTMW cites close to 300 empirical reports or literature reviews in evaluating specific hypotheses.
A&B conceal this from the reader. For example, they write, "Are wicked step-parents and parent-child conflict the natural outcome of genetic-payoff investment calculations? HTMW relies on readers' willingness to supply examples from their own lives . . ." No, HTMW relies on cross-cultural and ethnographic surveys, studies of of stepparents in the United States, and national statistics on child abuse and filicide (pp. 433-34).
Here is a particularly unfortunate example:
"There are many stories we tell ourselves. HTMW presents one that allows Pinker to . . . rationalize his particular view of relationships. Read as autobiography this may provide some insight, but as storytelling there are certainly more interesting organizing myths.
A&B do not explain my personal views of relationships, my autobiographical history, or how they claim to know them; their innuendo is another attempt to hide the empirical content of HTMW. The "story" in question is the theory of sexual selection and parental investment, and it is a clear counterexample to the claim that adaptationist hypotheses are sterile and unfalsifiable post hoc stories. Darwin first noticed an asymmetry in mating in much of the animal kingdom: males compete, females choose. In the 1960s and 1970s George Williams, John Maynard Smith, and Robert Trivers provided an elegant explanation in terms of parental investment: whichever sex invests more in offspring becomes a limiting resource for the other, and so the less-investing sex competes, the greater-investing sex chooses. In 1979 Donald Symons amassed a vast set of data on human sexuality that supported this theory, refuted competing adaptationist hypotheses, and made many new predictions about promiscuity, jealousy, mate selection, and physical attractiveness. In the 1980s and 1990s these predictions were tested in laboratory experiments, sociological data, in vivo field studies, surveys of the ethnographic literature, and cross-cultural surveys involving tens of thousands of people in thirty-seven cultures–and largely confirmed (pp. 460-93). A&B make no mention of these empirical tests, preferring snide, ad hominemremarks.
Finally, HTMW refutes A&B's cliche that "in adaptationist history/fictions that Pinker fancies there is no end to plausible story telling . . . we can always replace one adaptive story by another or add more modules as required, but [Pinker] offers us no way to reasonably refrain from doing so." A&B do not mention that a major conclusion of HTMW is that many of the most momentous human activities do not meet the criteria for adaptations, including written language, dreams, science, mathematics, music, art, religion, philosophy, and most narrative (pp. 174, 302-06, 340-42, and all of Chapter 8).5
1. Vision. In the chapter on vision, I suggest that the visual system uses a local, topographic, viewer-centered representation of visible surfaces and their depths, which David Marr called a "2H-D sketch" and which contemporary researchers have modified into what they call a "visual surface representation" (pp. 256-61). A&B claim that "practically no one" believes in it anymore. That is false. Recent overviews by leading perception psychologists such as Berkeley's Stephen Palmer and Harvard's Ken Nakayama rely on a modified 2H-D sketch; HTMW's discussion was based on a 1995 synthesis by Nakayama whose title tells a story: "Visual surface representation: A critical link between lower-level and higher-level vision." A&B cite "scientists at MIT" as disproving the visual-surface representation; when I showed two of them A&B's claim, the responses were: "To say 'no one believes in it' sounds overly strong. My sense is that surfaces of this sort remain quite popular, both in computer vision and in human vision," and "The claim you cite below is very misleading and exaggerated!"6
2. Behavioral Genetics. I report a near-consensus among human behavioral geneticists: that "much of the variation in personality-about fifty percent-has genetic causes." A&B assert that this naively confuses causation with correlation. I agree that A&B's definition of heritability-"the tendency of offspring to resemble their parents"-does not show that a trait is genetically influenced. But A&B have caricatured an entire field. The claim that variation in adult personality has substantial genetic causes is based on far more than that: that identical twins are more similar than fraternal twins, that biological siblings are more similar than adopted siblings, that these correlations are much the same whether the siblings are reared together or apart, that they remain even after one statistically controls for every possible contaminating factor ever proposed (including shared placentas), that these findings replicate across labs, decades, and countries, and that in several recent studies the variation has been tied to identifiable genes for neurotransmitters or their receptors or transpoters.7
Perhaps fearful that they cannot make the charge stick, A&B turn to other tactics. First, guilt-by-association: they triumphantly refute a silly nine-year-old quotation about IQ from a newspaper reporter. Second, misreporting: they write that I "evidently" rely on Thomas Bouchard's studies of "25" monozygotic twins. In fact Bouchard and his collaborators have studied over 1200 monozygotic twins (112 of them raised apart), and I cite reviews of converging studies of thousands of twins and adoptees conducted by independent teams in half a dozen countries. And finally, the political card: "Pinker's assertion is simply the authority of modern science pressed into the service of speculative fictions-truly biology as ideology." The latter is another trope from Lewontin, summarizing his theory that the current attention to DNA by molecular biologists is an attempt to root social problems in individual failings and thus preserve the status quo.8
3. Population genetics. A&B claim that HTMW falters by not presenting calculations from population genetics, the mathematical modeling of genetic change in evolution:
HTMW contains nothing–literally not one thing- resembling either evolutionary modeling, explicit fitness calculations, or the basics of population or behavioral genetics.
This is false. HTMW was written for a wide audience and does not present equations or proofs, but I explain many results from the explicit modeling of evolution. These include the fundamental theorem of population genetics (p. 163), models of the rate of evolution (pp. 163-64, 205), reconstruction of phylogeny through DNA comparisons (pp. 202-05), Hamilton's models of kin selection (pp. 398-401, 429-30), Trivers's formulation of reciprocal altruism (pp. 402-03, 502-04), Trivers's calculations on parental investment (pp. 440-42, 463-64), models of the genetic costs of incest (pp. 456-58), Grafen's modeling of sexual selection (pp. 500-01), Maynard Smith & Price's game-theoretic analysis of conflict (pp. 494-95), the game-theoretic analyses of bargains, threats, and promises by Schelling, Frank, and Hirshleifer (pp. 409-12), Rogers's calculations of age- and sex-specific discounting of the future (p. 498), Tooby & Cosmides's calculations on coalitional aggression (p. 514), and computer simulations of the evolution of neural networks (pp. 177-79), eyes (p. 164), and strategies of cooperation (pp. 503-04). Data on fitness are cited in discussions of children's age-specific value to parents (p. 452), incest (p. 456), male parental investment (p. 469), dominance (p. 495), and aggression (p. 510), among others. Behavioral genetics is discussed in pages 20-21, 448-449, and elsewhere.
It is true that I do not back up every hypothesis with mathematical models of changing gene frequencies, but then neither do biologists when they study the evolutionary function of the stomach or the eye. Pointedly, neither does Berwick himself in his own foray into evolutionary psychology, in which he confidently states that Chomsky's latest grammatical theory supports a saltationist account of the evolution of language.9
A&B claim to know of specific results from population genetics that undermineHTMW. First they say that population genetics casts strong doubt on whether adaptations can easily evolve: if genes combine in complex ways to determine phenotypes, then the fittest phenotype may not evolve. Of course, fit phenotypesdo evolve. Living things have improbable, intricately engineered parts: eyes and wings and lungs and immune systems and leaves and DNA repair and the other complex machinery that lets plants and animals stay alive. So the fact that some combinations of genes don't evolve into adapted phenotypes simply shows that organisms are not restricted to those combinations of genes over the evolutionary long run. A&B concede the point late in their review:
In recent conversation, James Crow, our foremost population geneticist, has insisted to us that if there were not some trait independence, evolution would grind to a halt, because any change would change all the traits in an organism and so nothing of lasting substance could be built. There is surely something to this.
There surely is, but they did not have to go to "our foremost population geneticist" to learn it. They could have asked me-or any biologist who treats population genetics as a tool to be applied with care and common sense, rather than as a weapon with which to beat opponents.
A&B's specific charge is that I am unaware of a seldom-cited twenty-year-old paper reporting a mathematical model in which "the entire kin-selection- maximize fitness [sic] edifice collapses." Since kin selection-the evolution of traits that benefit relatives because of their shared genes-is a cornerstone of the modern evolutionary analysis of social relations, this would appear to be a major flaw. But A&B's reporting is highly distorted.10
First of all, A&B are incorrect in saying that "Hamilton's original calculation was done only for haploid-diploid organisms where sisters have only half the usual number of chromosomes; this makes the bookkeeping easy, allowing us to conflate genes and genotypes." Or as Berwick put it in his other review ofHTMW in the Los Angeles Times, the "cost-benefit arithmetic doesn't balance the genetic books properly, unless you assume people are either ants or bees." In fact Hamilton published his results in two classic papers: the first analyzed the standard diploid case, the second extended it to the haplodiploid social insects.
Second, the paper by Feldman and Cavalli-Sforza does not say that in their interpretation, the entire edifice of kin selection "collapses." It says only that Hamilton's original results are "model-dependent"-a very different claim. Apparently A&B are unaware that in the ensuing two decades many mathematical biologists have developed plausible models in which kin-directed altruism can be proven to evolve, and without the bizarre parameter values that Feldman & Cavalli-Sforza deduced.11
There is a more general error in A&B's referring to population genetics as "the auto mechanics of evolution" and their implication that those who do not use it at every step are courting elementary errors. Models in population genetics are, by necessity, grossly simplified thought experiments about evolution over the short term. A typical model might posit two genes (compared to our 75,000), each coming in two or three alleles (compared to the astronomical numbers possible over the long term), with their interactions fixed (though the interactions themselves may change over the long term), and model the entire environment and entire phenotype as a single coefficient. As in economics, sophisticated mathematical models may be restricted to artificial toy worlds and have little connection to reality. One reformed population geneticist, a collaborator of Feldman's, has recently written:
It seems, thus, that the repeated failure to apply empirically the results of population genetic models to non-trivial evolutionary problems12< HREF="#12"> stems from an attempt to predict one process (say, long-term evolution) on the basis of a model, corresponding to another process (say, short-term evolution). This long-persisting attempt was based on the postulate, tacitly accepted by most in the field (the author of this note included), that at least qualitatively, the behaviour of the long-term process can be fully understood by extrapolation of the analytically well-defined short-term process. We see that this postulate is mathematically wrong.13
No doubt there is much to criticize in HTMW. But bystanders have a right to an accurate characterization of the book's content and of the relevant technical results. Readers of Ahouse and Berwick's review and of similar attacks on evolutionary psychology should ask: if the approach were really that empty, would these critics need to resort to so many misreportings, caricatures, and other questionable tactics?
1 Robert C. Berwick, The Acquisition of Syntactic Knowledge (Cambridge, Mass.: MIT Press, 1985).
2 Robert C. Berwick, "Syntax Facit Saltum: Computation and the Genotype and Phenotype of Language," Journal of Neurolinguistics 10 (1997): 231-49.
3 See HTMW, pp. 44-58 and 165-74, and my letter to the New York Review of Books, 9 October 1997; also Richard Dawkins, The Extended Phenotype (New York:
Oxford University Press, 1982), Daniel Dennett, Darwin's Dangerous Idea (New York: Simon & Schuster, 1995), and Robert Trivers's chapter in Sociobiology and Human Politics, ed. E. White (New York: D. C. Heath, 1981).
4 See Berwick, "Feeling for the Organism," Boston Review 21, no. 6 (December/January 1996), and the responses by Richard Dawkins, Daniel Dennett, and others in the following issue, BR 22, no. 1 (February/March 1997).
5 An irony in A&B's accusation about positing modules is that, Berwick, when arguing in the area of research in which we both work, is quite happy to "add more modules as required" in support of his critique of-surprise!-me: "We can show that the Pinker and Maratsos accounts are misguided. We can do a better job of explaining things via the interaction of two components of language, the morphological and the syntactic. By carving things this way, we shall arrive at an explanation where each "module" is simpler than one in which the explanatory burden is shouldered by the syntactic component alone." Robert Berwick and Amy Weinberg, The Grammatical Basis of Linguistic Performance(Cambridge, Mass.: MIT Press, 1984), p. 214.
6 A&B also misreport the Nature letter by Sinha & Poggio: It was Clinton's facial features, not his "head and shoulders," that were grafted onto Gore; Sinha & Poggio's conclusions were about head shape, not "global pose and stance"; Sinha & Poggio say nothing about a 2H-D representation, because their demonstration has nothing to do with it.
7 Plomin, R., "Environment and Genes: Determinants of Behavior." American Psychologist 44 (1989): 105-11; "Genes and Behavior: A Special Report," Science 17 (1994): 1685-1739; Special issue of Current Directions in Psychological Science on Behavioral Genetics, (October 1997); Dean Hamer, Living with Our Genes, (New York: Doubleday, 1998). The Devlin et al. Natureletter that A&B refer to is highly tendentious and is answered by Thomas Bouchard in a forthcoming issue.
8 Richard Lewontin, Biology as Ideology: The Doctrine of DNA (New York: Harper Collins, 1991).
9 Berwick, "Syntax facit saltum."
10 A&B unsystematically insert Trivers's very different theory of reciprocal altruism into their critique, but kin selection is the theory relevant to Hamilton and to Feldman & Cavalli-Sforza's principal model and to A&B's mention of step-parents that kicks off their discussion.
11 See, for example, B. Charlesworth and E. L. Charnov, "Kin Selection in Age-Structured Populations," Journal of Theoretical Biology 88 (1981): 103-19; P. D. Taylor and S. A. Frank, "How to Make a Kin Selection Model," Journal of Theoretical Biology 180 (1996): 27-37; P. D. Taylor, "Inclusive Fitness Arguments in Genetic Models of Behaviour," Journal of Mathematical Biology 34 (1996): 654-674; and A. Grafen, "A Geometric View of Relatedness," Oxford Surveys in Evolutionary Biology 2 (1985): 28-89.
12 See for example Richard C. Lewontin, The Genetic Basis of Evolutionary Change (New York: Columbia University Press, 1974).
13 I. Eshel., "On the Changing Concept of Evolutionary Population Stability as a Reflection of a Changing Point of View in the Quantitative Theory of Evolution." Journal of Mathematical Biology 34 (1996): 485-510.
Steve Pinker suggests that when stripped of vehemence, we all agree that the brain is not just a uniform gray custard, that "processing" lurks behind the mental, and that we share a naturalistic commitment to biology and evolution, including natural selection. But beyond this catechism, we differ more than Pinker's rhetorical narrowing indicates. He suggests that we really disagree only about "which mental processes are functional adaptations." That is a basic point of contention: we think Pinker is much too quick to explain the evolution of mental processes by assigning them adaptive functions. But many of the other difficulties in How the Mind Works (HTMW) follow from his promiscuous adaptationism: reporting premature consensus where there is none; uncritically describing behaviors as genetic, implying that they were optimal solutions to an diffusely described past and thus naturalizing them as inevitable; underestimating the sheer difficulty of adaptationist arguments; identifying "innate mental faculties" with "traits"; and embracing a "Darwinian fundamentalism" that effectively equates evolution with natural selection.
Nothing in Pinker's reply urges us to step back from these conclusions. Does Pinker now demonstrate that any behavioral disposition, even "sexual desire" has a coherent evolutionary history or segregates just like the gene for wrinkled peas? No. Does he now establish that only one selective explanation-his- exists for any (hypothetical) trait, paying attention to the space of selective alternatives, physical possibilities, and empirical contingencies? No. Does he probe the selectional regimes 100,000 years ago? The assumption that genetic equilibrium was attained then, the commandeering pace of cultural evolution since? No, none of these things. We did not ask that he turn his book into a technical treatise-we pointed out that he provides none of the technical details.
Panselectionism and Other Distortions
To us Darwinian fundamentalism is a form of irrationalism that, left un-checked, erodes the very theory of evolution it embraces. We are repeatedly told that functionality, design, and adaptedness are explained by only one known physical mechanism: "Natural selection remains the only theory that explains how adaptive complexity, not just any old complexity, can arise" (p. 162); "Because there are no alternatives, we would almost have to accept natural selection as the explanation of life on this planet even if there were no evidence for it" (p. 162); "[natural selection] alone explains what makes life special" (p. 155, our emphasis). But appeal to this doctrinal ("indispensable") principle is coherent only if there is a criterion for functionality, design, and adaptedness that is independent of the actual existence of traits-otherwise, we can "explain" all adaptations, or their negations, equally well. And to this point we have no such independent criterion. HTMW suggests that "reverse engineering" is the independent measure-but we challenged this underpowered metaphor in our review and Pinker did not respond to this either.
Traits and adaptations are simply not obvious. Is it really so clear, as HTMW says, that "sexual desire" is an adaptation to beget children? We already noted in our review that it is controversial why sex originated-increasing genetic variance? parasite defense? mutation elimination?-let alone sexual desire. We simply do not yet know. Why do we see in three dimensions? The answer, to "see in depth," is a near tautology. And it is probably not to recognize objects, contrary to the "consensus" that is presented in HTMW for the now modified "2H-D sketch."1
On the other hand, take HTMW's "obvious" nonadaptation, music. Darwin conjectured music was adaptive, and devoted a whole section to it in The Descent of Man and Selection in Relation to Sex (pp. 496-501). If the answer is not obvious in cases where the traits are relatively easy to measure, then what of our mental capacities and the more plastic, behavioral repertoires associated with them? Allowing that they may well be adaptive, which we do, is not the same as insisting that virtually all are adaptive and that we know why, which is how it is presented in HTMW.
Pinker's response to our description of his position as panselectionist is to complain about distortion and quote a series of one-line caveats that (supposedly) demonstrate that he is aware of our points, anticipated them, and agrees with us. But consider his principal example of distortion. We quoted him as saying: "Why don't women give virgin birth to daughters who are clones of themselves instead of wasting half their pregnancies on sons who lack the machinery to make grandchildren and are nothing but sperm donors?" He responds that, taken in context, the point of the remark was that "sex is puzzle for all organisms; humans are presented just as an example." But this was precisely what we rejected: humans are not a good example for understanding the payoff schedule that could select for sexual reproduction, and neither are any other mammals, from aardvark to zebra (nor would any number of many other clades be a good example, e.g., birds). Our point was that structural constraints on evolution might provide the answer to Pinker's question about sexual reproduction. But the notion that there are structural constraints explaining a trait's state is apparently so remote from Pinker's concept of evolution that even when we raise the possibility, he restates (with emphasis) his misunderstanding.
As to the one-line caveats: We noted in our review that Pinker's text includes such hedges and comments, but they are never taken to heart and will not make the rest of the book go away. He really does have to defend his uncorsetted story-telling (the longest chapter, "Family Values," is his exegesis of evolutionary psychology-inspired morals). So we must ask readers to return to our review and see if the examples we challenge are really so unmotivated by the text. Or consider the passages on elephant trunks and evolution (pages 152-53); or cognitive "closure" and the limits of adaptations (pages 558-65). Though we welcome the caution in Pinker's response, our complaint remains: HTMW is a popularization that lacks the spirit of doubt that suffuses scientific practice.
One kind of caveat deserves special mention. This is his widely quoted defense of choosing not to have children thus subverting evolutionary imperative, "and if my genes don't like it they can jump in a lake." In a book whose unrelenting message is that our behaviors were optimized and branded into our genes on the savanna (100,000 to a million years ago) this sudden embrace of genic independence strikes us as merely diversionary, hardly a constitutive part of the view Pinker is defending, according to which "the biggest influence that parents have on their children is at the moment of conception" (p. 449). While conception is a necessary step on the path to a child, Pinker's claim, to be interesting, must be at least partly causal. This is why we find his objection to our accusation of genetic determinism curious. Here again, he drives the narrative forward by making claims that sound strong and controversial only to turn them bland and incontestable through qualification.
One final point on this topic: Pinker resents our implication that his evolutionary stories reflect no more than his biography. Fair enough. We do not know the details of his life or motivations, and were too quick to suggest that his stories only reflect his biography. We offered this hypothesis after having slogged through the book, and found ourselves unconvinced by his insistence that the conclusions are forced on him by data, unmediated by his predilections. Wherever they come from we still insist that there are richer and more interesting organizing myths.
Structure and Function
For those outside evolutionary biology, the stakes in the debate about the extent of functional adaptation may seem esoteric, so some background may be useful. Arguing from function to structure (the explanation for the heart's structure is its function, pumping blood) is an example of teleological thinking. Reasoning from "final causes" is disreputable when discussing systems that lack intention (primarily because it seems to be future states reaching back to form what will be). No one has a problem with saying a pot looks the way it does because the artisan wanted to make it that way, though even here the medium can push against the intentions of the creator. Darwin salvaged this form of thinking in biology through a clever insight, natural selection. After Darwin, function-centric teleological accounts became a kind of shorthand, able to unroll into a more elaborate hypothesis involving variation, heritability, and selection.
A counter-tradition and useful dialectical tension for functionalism is structuralism, an emphasis on conserved structures.2 To return to an earlier example: the explanation of sexual reproduction in humans need not appeal to the function of sexual reproduction in humans-rather, the explanation may well be a matter of constraints and options earlier in this lineage. The selectionist argument that allows us to speak teleologically about a trait requires that the population have variance in the trait. HTMW claims that all of the uniquely human traits emerged through selection on the savanna. But we do not know the variance in human populations with respect to behavioral traits 100,000 years ago, nor do we know the heritability of these dispositions. Unambiguous function assignment is difficult in any case, and from the distance of over a hundred millennia the data you would use to make tentative assignments is quite meager.
Structuralism faces a symmetrical challenge: identifying structures that are "the same" (homologies). These two perspectives provide an essential tension. In the late 1800s functionalism associated itself with evolution and structuralism was associated (by functionalists) with special creation. This has left an unfortunate residue, for as special creation was dismissed structuralism sank with it. Rather than a creative tension between these positions we have the odd situation where some evolutionists assign notions of historical, developmental, or structural constraints to footnotes and caveats. Fortunately, with the string of successes in developmental genetics in the last decade this is changing.3 The distance between a view that prefers a functional-structural dialectic and one that recognizes function as central and anything else as minor epicycles may help explain the rift between Pinker and us.
In part, the differences are matters of temperament: some are content to study the mind and its properties, others insist that we must first agree that the properties are adaptations (even if they can't deliver on the full account that adaptations demand). To us, studying the properties is the interesting thing, not asserting that they are adaptations and then studying them. Moreover, we think that the realization that brains and neurons are homologous structures has been methodologically much more productive (allowing us to do neurobiology by studying mice, crayfish, flies, octopus, and sea hares).
Finally, what are we to make of the suggestion that we (along with Stephen J. Gould, Steven Rose, and Philip Kitcher) are puppets hanging from Dick Lewontin's old and bitter fingers? Well, it is high praise indeed. If we reflect Lewontin's admirable writings, and this puts us on the dais (or in the dungeon) with other compelling writers, we welcome the association. When Steve Pinker asserts that we are all suspicious of attempts to connect psychology with standard evolutionary biology, he is right! We do not believe that nearly enough is known at present about psychology or evolution to link them. But it is possible to link a caricature of each, and this is what we found in HTMW.
Richard Feynman put it well. Our responsibility is to give all the detail to "help others judge the . . . contribution; not just the information that leads to judgment in one particular direction or another." The challenge in science writing, indeed science itself, is to tell a crackling good tale abiding the dramatic unities, while respecting scientific ambiguity, details, and unresolved tensions. Pinker's previous book The Language Instinct succeeded here precisely where HTMW fails, and for exactly this reason: the earlier book drew on a forty-year consensus about generative grammar patiently constructed by Noam Chomsky and colleagues, while HTMW forces one prematurely. So when we wrote "You need not believe a word of it" we meant just that: Evolutionary psychology does not force your hand (or your mind) here. You ought to judge for yourself. Pinker could have helped that judgment by presenting alternative explanations antithetical to his views in enough detail. But he didn't.
1 Pinker missed our point about Marr's 2H-D sketch. Of course some people still "believe" in it-though it is important to clear about just what they believe. All we needed to illustrate was a lack of consensus to make our point that his reporting was skewed. According to David Marr's former colleagues, Profs. Shimon Ullman, Tomaso Poggio, Berthold Horn, and Eric Grimson, who, together with Marr, came up with the notion of 'visible surface representation' known as the "2H-D sketch" it was meant to be an integrated representation for surfaces on the way to object recognition. HTMW's picture on page 260, which depicts the 2H-D sketch as a circle and then writes out separate, distinct slots for depth, slant, tilt, color, and surface identification is misleading. Visual surface reconstruction seemingly does matter for certain low-level visual tasks like figure-ground separation, but not, according to Ullman, Poggio, and Heinrich Buetlehoff, for object recognition, not even for 3-D. Further, there is really no hard biological evidence for such a surface representation-scientists simply have not found neurons that respond to surface orientation regardless of where it's coming from. Evidently, neurons behave differently. Moreover, the 2H-D sketch recorded local surface orientation, not really depth (Berthold Horn at the MIT AI Lab did much of this work at MIT in the late 60s and early 1970s, attracting Marr there in the first place). But our point was not to quibble about these details or history: it was simply to point out that nobody had gotten the integrated representation to work (which of course does not bar somebody else from trying to make it work), and that this integrated representation is not a consensus in the field.
2 R. Amundson, "Typology reconsidered: Two Doctrines on the History of Evolutionary Biology" Biology & Philosophy 13, no. 2 (1998):153-77
3 J. Gerhart and M. Kirschner, Cells, Embryos, and Evolution. (Cambridge: Blackwell Science, 1997); Brian Hall, Evolutionary Developmental Biology(New York: Chapman & Hall, 2nd edition, 1998).
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