essentialism and selectionism in cognitive science …...essentialism and selectionism in cognitive...

Essentialism and Selectionism in Cognitive Scienceand Behavior Analysis

David C. PalmerJohn W. Donahoe

Smith CollegeUniversity of Massachusetts/Amherst

Contingencies of selection, be they phylogenetic or onto-genetic, merely set boundaries on units; they do not provideblueprints. Thus, variability is fundamental to all productsof selection. Skinner, by characterizing the units of analysisin behavior as generic in nature, established his sciencesquarely within the selectionist paradigm, thereby avoid-ing the tendency, common throughout psychology, to slipinto essentialist analyses. The distinction between essen-tialism and selectionism is refined in this article, andprominent examples of essentialism in linguistics, theoriesof memory, theories of representation, associationism, andeven in behavior analysis are identified. Recent trends incognitive science—specifically, research on adaptive net-works—is amenable to a selectionist interpretation, sug-gesting the possibility of future fruitful interactions withbehavior analysis.

In this article we import a distinction from evolutionarybiology—that between selectionism and essentialism—to discuss contrasting trends in cognitive science. Largelybecause of the prestige of Darwin's theory, essentialismis out of fashion as an explicit doctrine in science. How-ever, one can pay lip service to selectionism and still sub-scribe to essentialist assumptions, employ essentialist lo-cutions, define essentialist units of analysis, and worse,pursue research guided by these assumptions, units, andlocutions. In contrast to most of his contemporaries,B. F. Skinner consistently repudiated essentialism (al-though he never used the term) both in his science andin his verbal behavior. Of particular significance, we argue,was Skinner's early methodological claim that the ap-propriate units of analysis in a science of behavior are tobe defined empirically, rather than a priori (Skinner, 1935,1938). By putting this claim into practice, Skinner setthe stage for a thoroughgoing selectionist science and soavoided much of the fruitless inquiry engendered by im-plicit essentialist assumptions. The field of behavior anal-ysis has generally, although not always, hewn to Skinner'sprecepts and remains psychology's most consistently se-lectionist enterprise. In contrast, many contemporarycognitive scientists, while accepting selectionism at thephylogenetic level, explicitly reject Skinner's positionwithout subscribing to an alternative selectionist meth-odology; consequently, much normative cognitive science,

we argue, is prone to essentialist assumptions and locu-tions that have engendered research, which, from a se-lectionist's point of view, is uninterpretable. In our opin-ion, the distinction between behaviorism and cognitivismis less fundamental than the distinction between selec-tionism and essentialism. Behavior analysts are well ad-vised to consider those cognitive analyses that are selec-tionist and question any behaviorist analyses that smackof essentialism. We close on the optimistic note that cur-rent trends in cognitive science, particularly the growinginterest in adaptive networks, or parallel-distributed pro-cessing, are amenable to selectionist interpretations. Thissuggests the possibility of fruitful interactions betweensuch models of cognition and radical behavioral accountsof complex human behavior.

Essentialism and Selectionism ContrastedDarwin's theory of evolution by natural selection is stillhotly disputed in some quarters, but there are few in thescientific community that doubt that the theory, at leastin its broad outlines, accounts for the extraordinary com-plexity and diversity of living things. The elegance of thetheory lies in the unparalleled simplification that itachieved; countless acts of special creation were replacedby the repeated action, over the eons, of a relatively few,elementary processes. Although selective breeding hadbeen practiced for millennia, the power of selection toexplain adaptive complexity in nature was not cogentlyargued until Darwin unveiled The Origin of Species in1859. Despite its elegance, Darwin's theory languishedwithout widespread acclaim until its synthesis with pop-ulation genetics in the 1930s. If selection was slow to berecognized for its role in phylogeny, it was slower still tobe recognized as a nonteleological explanation for a widevariety of other complex phenomena, including operantconditioning (e.g., Thorndike, 1898), the immune re-sponse (Jerne, 1955), problem solving and the acquisitionof knowledge (e.g., Campbell, 1960, 1974; Popper, 1972),cultural practices (e.g., Campbell, 1975; Skinner, 1948,

Correspondence concerning this article should be addressed to DavidC. Palmer, Department of Psychology, Smith College, Northampton,MA 01063 or to John W. Donahoe, Program in Neuroscience and Be-havior, Department of Psychology, University of Massachusetts, Amherst,MA 01003.

1344 November 1992 • American PsychologistCopyright 1992 by the American Psychological Association, Inc. 00O3-066X/92/S2.O0

Vol. 47, No. II, 1344-1358

1971, 1981), perception (Campbell, 1956b), neural net-works (e.g., Edelman, 1987), and technological innova-tions (e.g., Basalla, 1988; Root-Bernstein, 1989). Selec-tionist interpretations have been provided for phenomenaas disparate as the locomotion of protozoa (Baldwin,1895; Campbell, 1956a) and the orderly orbits of plane-tary bodies (Donahoe, Burgos, & Palmer, in press). As inthe case of speciation, even when underlying mechanismsare poorly understood, selectionist accounts are appealingbecause of their simplicity and power.

Selectionism is gradually replacing what the evolu-tionary biologist Ernst Mayr called essentialist thinking,the tendency to view categorical phenomena in nature asreflections of universal, enduring qualities intrinsic to eachclass or unit (Mayr, 1976, 1982, 1988).1 In Darwin's day,the dominant view of living things was essentialist in thissense; species and other classes of organisms were seenas collections of individuals that all shared some essentialproperty that denned the group, and taxonomy was largelya matter of identifying these essential properties. Individ-uals within a group might vary widely, but they were allseen as variants of a single template. Individual variabilitycould be explained as the outcome of less fundamentalfactors—crossbreeding, environmental stress, accident, orother vicissitudes.

Of course this position leaves unexplained the originof the templates. It is characteristic of essentialism thatphenomena are said to reflect some ideal, some essence,or some template that in itself remains unexplained. Thedevout presumably attribute the origin of templates to adeity. Certainly, much of the bitterness with which Darwinwas attacked arose from the implication that naturalphenomena could be explained without reference to adesigner. Nevertheless, one does not have to be a deist tobelieve that species have essential properties; the skepticmerely adds the origin of templates to the list of naturalphenomena that we accept as unexplained, perhaps evenas unexplainable.

Darwin's (1859/1950) discussion of the term speciesis clearly at odds with the essentialist position. He noted,

No one definition has satisfied all naturalists; yet every naturalistknows vaguely what he means when he speaks of a species.Generally the term includes the unknown element of a distantact of creation. . . . It is certain that many forms, consideredby highly-competent judges to be varieties, resemble species socompletely in character, that they have been thus ranked byother highly competent judges. But to discuss whether they oughtto be called species or varieties, before any definition of theseterms has been generally accepted, is vainly to beat the air.. . .It will be seen that I look at the term species as one arbitrarilygiven, for the sake of convenience, to a set of individuals closelyresembling each other, and that it does not essentially differfrom the term variety, which is given to less distinct and morefluctuating forms. The term variety, again, in comparison withmere individual differences, is also applied arbitrarily, for "con-venience" sake. (pp. 24-29)

Of course it was not Darwin's linguistic or philo-sophical predilections that aroused his contemporaries,but his exposition of selection as a non-teleological ex-

planation of the diversity of life. Evolution requires onlythat there be heritable variation among individuals andcontingencies of selection that operate overtime. Selectionis a process that necessarily takes time: When contingen-cies of selection are stable over the duration of one's ob-servations, species may appear to have essential properties,but Darwin showed that this appearance of stability isquite consistent with a selectionist account. When viewedover time, it is clear that the individual is a unique con-stellation of properties that can only be understood, notby considering one's group membership, but by consid-ering, in detail, the environment-organism interactionsof one's ancestors.

However, it means something to say, for example,that a fox is a fox and not a mouse. Presumably all foxesshare a common ancestor, and as they breed with oneanother and not with dissimilar species, they have a strongfamily resemblance. In addition, all foxes are subject tosimilar contingencies of selection. Do not the contingen-cies of natural selection specify the essential propertiesof species? To argue so is to overlook a crucial feature ofevolutionary phenomena. Foxes will vary from one an-other within bounds determined by the selection contin-gencies. Any variant that satisfies the contingencies canmake a contribution to future generations of foxes.Moreover, although we speak of contingencies of naturalselection in general terms, the contingencies are as indi-vidual as the organisms themselves. For example, wemight observe that a changing climate favored foxes withheavier coats or that brilliant plumage in a species of birdwas more effective in attracting mates. However, survival

1 Mayr (1976, 1982, 1988) borrowed the term essentialism fromPopper (1957), who coined it as an unambiguous substitute for the over-worked term realism. The realists were scholastic philosophers who,quibbling over the exegesis of Aristotle, held that categories are dennedby essential properties that transcend the specific members of the cat-egories. The category of white things, for example, is defined as thoseelements that possess the property of "whiteness." Whiteness is an es-sence, a "thing" that we come to know in its own right through ourexperience with white objects. This position can be traced back, in someform, to Plato and Parmenides. In contrast, nominalists (chiefly followingWilliam of Occam) held that universal terms such as white were merelabels that we use for a collection of objects of a common color. Theydo not represent things with an existence or status independent of theset of white objects. Hobbes (1651 /1968) captured the nominalist positionin his discussion of the distinction between proper nouns and commonnouns. Of the latter, he noted, "Every one of which, though but onename, is nevertheless the name of diverse and particular things; in respectof all which together, it is called a universal, there being nothing in theworld universal but names; for the things named are every one of themindividual and singular. One universal name is imposed on many thingsfor their similitude in some quality, or other accident" (p. 102). Locke(1690/1975), in hisEssayon Human Understanding, foreshadowed muchof the discussion in the present article by distinguishing between whathe called "real essences" and "nominal essences," that is, between prop-erties that are intrinsic and those that are conventional. He held thatonly humanly denned categories such as circle and Whig could be saidto have real essences. Natural categories such as man were conventional;he noted that occasionally infants were born so deformed that it wasunclear whether they qualified as exemplars of the category human.Although circles have defining properties that, in a sense, precede anyinstance of a circle, natural categories such as sheep, tree, or man donot have defining qualities, except by convention.

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is a matter not of global contingencies but of the moment-to-moment contingencies of an individual's life. A light-coated fox might thrive in a region where food was abun-dant, and a modestly plumed bird might find a mate ifcompetition were scarce. Although, on the average, it maybe true that the race is to the swift and the battle to thestrong, the average organism is an abstraction; onlyindividuals exist, and time and chance happeneth tothem all.

The role of genes—unknown to Darwin—does notaffect our conclusion. Genes are templates, to be sure,but constellations of genes are variable within a species,even from parent to offspring, and they are continuallysubject to mutation. Indeed, without this variability, evo-lution would be impossible. Selection does not produceorganisms stamped out of a common mold. To the con-trary, a bizarre mutation that eliminated variability in apopulation would surely prove fatal when prevailing con-tingencies changed.

Thus, contingencies of selection do not yield rigid,static, or idealized species, nor do they select rigid, static,or idealized properties of species. The selected property,be it a morphological feature or a behavior, can vary inany arbitrary characteristic that is incidental to the con-tingency, but, more fundamentally, it can even vary alongthe dimensions that are defined by the contingency. Aselection contingency merely sets minimum standards fora property; it does not provide a blueprint. Variationwithin the boundaries of the selection contingencies willbe constrained only by those mechanisms that generatevariability in the property. The critical difference betweenessentialism and selectionism, then, is that selectionismregards variability within classes of phenomena as fun-damental, whereas essentialism regards it as a misleadingirrelevance.

Selection and BehaviorThe analogy between natural selection and learning hasstruck several observers, apparently independently (e.g.,Baldwin, 1895, 1909/1980; Campbell, 1956a; Pringle,1951; Skinner, 1953; Staddon, 1983). Thorndike (1898)provided the first systematic analysis of reinforcement:A cat in a puzzle box emits a wide variety of behaviors;some variants affect the apparatus in such a way that thedoor falls open, allowing the cat to escape; on later trialsthese successful variants are more likely to occur. As inevolution, variable elements have different consequences;those with certain kinds of consequences are strengthenedrelative to the unsuccessful elements. Order emergeswithout appeal to a designer or to intentionality. Skinner(1938) noted that highly organized, complex behaviorcould be shaped from relatively undifferentiated baselinebehavior by successive contingencies of reinforcement inwhich the selection criterion was gradually altered to moreclosely approximate some target behavior, just as grad-ually changing climate, habitat, competing species, andso on, presumably shaped highly organized, complexstructures or innate behaviors in organisms (Skinner,1966b). Thus, both evolution and reinforcement operate

by repeatedly selecting elements from a variable substrateto produce orderly classes of phenomena. In behavior asin morphology, variability is required if selection is tocreate new forms.

The behavioral repertoire of an organism reflectsboth phylogenetic contingencies and contingencies of re-inforcement. Consequently, variability is a fundamentalcharacteristic of behavior, even under the most restrictedcircumstances. Abstraction, idealization, categorization,and averaging cannot eliminate this variability; it can onlymask it. We err in our science if we treat the variabilityof our subject matter as an annoying irrelevance that canbe eradicated by such practices.

Implications for Units of Analysis inCognitive ScienceIn the behavioral sciences no one has been a more thor-oughgoing selectionist than Skinner, for he has interpretedall behavior—from lever presses to perception, verbal be-havior, and thinking—in terms of principles of selection.But Skinner's place in the pantheon of selectionists doesnot rest primarily on his verbal interpretations, importantthough they are in showing the scope of these principles.Rather, his main contribution was the methodology thatarose from his prescient grasp of the nature of his subjectmatter. Skinner recognized that variability was funda-mental to behavior and fashioned his methodology ac-cordingly. In particular, he realized that the appropriateunits of analysis in a science of behavior are generic innature. In this regard, so far as we know, he was unique.

Skinner's Empirical Units of Analysis

As Skinner (1935, 1938) observed, if we want our unitsof analysis to respect lines of fracture in nature, we mustdefine them empirically. We cannot define them fromour armchairs; rather, we must survey the variability ofour subject matter and adopt working definitions accord-ing to the order we find. Skinner was not making a phil-osophical claim; he observed that the order that emergedin his investigations rested upon adopting empirically de-termined, generic units of analysis.

According to Skinner, the search for orderly unitsof behavior and environment begins arbitrarily. The ex-perimenter has a hunch, follows a precedent, or picksdefining properties of his units at random. If the dynamicproperties of behavior are not orderly when the units areso defined, the experimenter systematically restricts ormodifies the definitions until orderly relationships be-tween variables emerge. For example, in the study of theflexion reflex in a spinal preparation, Skinner (1938)wrote,

If we are measuring fatigue, for example, we shall not obtaintoo smooth a curve if our stimulus varies in such a way as toproduce at one time one direction of flexion and at another timeanother; but as we restrict the stimulus to obtain a less variableresponse, the smoothness of the curve increases, (p. 36)

The process of modifying these definitions can continueto the point at which both environmental and behavioral

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units are completely restricted. Here we choose to countonly those stimulus and response events that meet verynarrow definitions. For example, we might define the re-sponse in terms of specific effectors, precise location,force, latency, and so on. However, Skinner noted thatnothing is gained by continuing to restrict these defini-tions past a certain point:

The generic nature of the concepts of stimulus and response isdemonstrated by the fact that complete induction obtains (andthe dynamic changes therefore reach an optimal uniformity)before all the properties of stimulus and response have beenfully specified in the description and respected in each elicitation.(p. 37)

Extending the analysis to operant behavior, Skinner notedthat, in the process of restricting our definitions, an in-flection point is reached at which our data are most or-derly. Continued restriction actually leads to a deterio-ration in the orderliness of the data. Consider barpressingin the rat:

Before we can see precisely what a given act consists of, we mustexamine the changes it undergoes in strength. Here again wemerely specify what is to be counted as a response and refuseto accept instances not coming up to the specification. A spec-ification is successful if the entity which it describes gives smoothcurves for the dynamic laws.. . . The number of distinguishableresponses on the part of the rat that will give the required move-ment of the lever is indefinite and very large. They constitute aclass which is sufficiently well defined by the phrase 'pressingthe lever.'. . . The members of the class are quantitatively mu-tually replaceable in spite of their differences. If only such re-sponses as had been made in a very special way were counted(that is, if the response had been restricted through further spec-ification), the smoothness of the resulting curves would havebeen decreased. The curves would have been destroyed throughthe elimination of many responses that contributed to them. . . A respondent, then, regarded as a correlation of a stimulusand a response and an operant regarded as a functional part ofbehavior are defined at levels of specification marked by theorderliness of dynamic changes, (pp. 37-40)

Note that Skinner was not recommending that we simplymanipulate our independent variables until orderemerges; he was recommending that we modify our def-initions until order emerges. That is, a single set of ob-servations might yield either orderly or disorderly rela-tionships, depending on what we choose to count as stim-ulus and response events.

Skinner explicitly rejected the practice of ad hoccategorizing of stimulus and response units. When a boyhides from a dog, it is a mistake, he averred, to assume,uncritically, that the dog is a stimulus or that hiding is aresponse. Such practices may be useful in interpretingbehavior outside the laboratory but should be avoided inthe basic science. Skinner also rejected Watson's (1930)definition of a response as "anything the animal does,such as turning toward or away from a light, jumping ata sound, and more highly organized activities such asbuilding a skyscraper, drawing plans, having babies, writ-ing books and the like" (cited in Skinner, 1938, p. 42).

Clearly, the latter activities do not share the orderly prop-erties of barpressing or turning toward a light.

Skinner justified his position on pragmatic grounds,declining to speculate whether methodological advanceswill permit fruitful analyses of fully restricted units.However, he might have justified it on principled groundsas well: Generic units of analysis follow from a commit-ment to selectionism. As noted earlier, contingencies ofselection cannot yield idealized units; variability is fun-damental. Selection contingencies merely set bounds onwhat is possible; they do not prescribe designs.

The effectors that enable a rat to press a bar werepresumably selected for their contribution to foraging,climbing, running, and so on. A particular act, say, ex-tension of the forepaw, contributes to each of these ac-tivities, and the structures participating in the act can beexplained in part by reference to contingencies of naturalselection. Not only do these contingencies tolerate vari-ability in form from one instance to the next, but suchvariability is actually necessary if reinforcement contin-gencies are to shape effective locomotion in an unevenenvironment. Variability of response topography is notonly unavoidable, it is adaptive. Skinner's generic units,then, are analogous to species: The units are orderly butare neither arbitrary nor invariant.

Skinner's analysis of behavioral units establishes hisscience squarely within a selectionist paradigm. Moreover,without his methodological precepts there could be nojustified inductions in the analysis of behavior and henceno science of behavior; nor could there be plausible in-terpretations of complex phenomena based on that sci-ence. Despite the importance of Skinner's analysis, hisviews on the subject are virtually unknown outside thefield of behavior analysis. Actual practice in normativecognitive science is more consistent with essentialism.Units of analysis are usually defined a priori, formally,or are taken as self-evident.

A Priori Units of Analysis

Some concepts have formal definitions, presumably pro-posed by one individual and adopted, without complaint,by others. Centuries ago, someone defined a dodecahe-dron as a regular polyhedron with 12 faces, and the def-inition has served us well ever since. Deciding whethersomething is a member of the class is merely a matter ofinspecting the candidate in the light of the definition. Ifasked whether a particular garnet crystal is a dodecahe-dron, we can examine it and assert, with complacency,that no, although it has 12 faces, it is not regular at thethird decimal place. Some may balk at such pedantry—surely the concept of dodecahedron was defined in orderto capture the regularity of garnets and other crystals—but there is no requirement that a concept with a formaldefinition map onto the dusty and spotted stuff of thereal world.

To the contrary, concepts with formal definitions donot map onto the natural kinds of the real world. We treatsome phenomena categorically before we try to definethem—garnet crystals, for example. In such a case we


may try to define the class, but our attempt requires notimposing a definition but discovering one. We must studycrystals, and we may, at length, settle on a definition thatseems to embrace an appropriate group. Nevertheless, onfurther study we are sure to find a crystal that seems asthough it ought to qualify as a garnet but that just failsto meet our definition. The crystal has some impurity orirregularity that we had not anticipated. (Defining theclass in terms of its chemical structure, for example,would include only pure garnets—if there are any—orpure parts of impure crystals, thus missing the general-ization that we set out to capture.) We may modify ourdefinition, or we may just decide that, although imperfect,it is good enough. Our empirical definition will have someslack in it, uncharacteristic of a priori or formal defini-tions. Thus, the problem for the scientist is to determinethe natural lines of fracture of the phenomena understudy.

The task of determining these lines of fracture is thetask of finding order in our subject matter. Order is partly,of course, in the eye of the beholder, thanks to a particulargenetic makeup, a particular personal history, or a par-ticular practical contingency—all of which involve con-tingencies of selection. Although garnet crystals may seeman obvious and well-established category to a mineralo-gist, they surely do not to a sea slug or to many an un-schooled human, for that matter. A chicken will see littleto choose between a fox and a coyote but will make muchof the difference between a worm and a caterpillar. Hon-eybees will swarm to buckwheat in the morning but forageelsewhere in the afternoon, bewildering the farmer, whosees no difference. On the other hand, regularities in theworld presumably do not wait upon an observer; the applewould still have fallen, even if Newton had overslept. Buthow these regularities affect the observer is a matter ofcontingencies of selection.

Categories with formal definitions or categories de-fined a priori can be said to have essential properties,properties that, in a sense, precede any example of thecategory. We are free to define such categories as weplease, and they need not reflect distinctions in nature.If we choose to define human beings as featherless bipeds,then we cannot object to including Tyrannosaurus rex.As it is considered good scientific practice to define one'sterms, researchers may be tempted to define their termsbefore the data are in, and, in effect, provide a formaldefinition for a concept that is more appropriately definedempirically. Doing so may be harmless, but it invites es-sentialist thinking into a domain shaped, at least in part,by contingencies of selection. The problem is not uniqueto cognitive science. The evolutionary biologist BenjaminBurma (1949) voiced the following lament about the spe-cies concept:

In some respects it is extremely unfortunate that names everget attached to ideas or objects. The false attachment of namesto ideas or objects similar but not identical with the originalcan work harm far exceeding the benefits conferred by havinga convenient label. The name "species" has come to such astate, (p. 369)

In biology and psychology, orderly classes of phenomenawill have all the variability characteristic of products ofselection. Such categories, then, will be fluid both becausethe exemplars of a category will have varying propertiesand because the boundaries of the category will dependupon the demands and characteristics of the observer.But it is a rare cognitive scientist who defines his termsempirically. In its flight from the restrictions of behav-iorism, cognitive science has abandoned this importantmethodological constraint. Consequently many cognitiveconcepts retain a strong essentialist flavor.

Some Difficulties With Essentialist Units of Analysis

It is our thesis that essentialist thinking is no more ap-propriate in behavioral or cognitive science than it is inevolutionary science. Selection is the only natural processyet proposed for explaining adaptive complexity in nature(Dawkins, 1986), and we argue that this is as true forbehavior as it is for morphology. (Note that this is not toclaim that all structures or behaviors have been specifi-cally selected. As we have argued, selection is a blunt toolthat permits, and therefore ensures, variability.) An anal-ysis of a behavioral phenomenon in essentialist terms maywell be better than nothing, but it can be more profitablyrecast in selectionist terms. Moreover, essentialist analysesare prone to the following problems.

Temptation to circular reasoning. In the worst case,essentialism attempts to explain a behavioral phenome-non by inventing a property of the organism responsiblefor the phenomenon. Because behavioral phenomena arepresumably, at least in part, a function of properties ofthe organism, this seems an innocent step. However, thehypothetical property often is later invoked as an expla-nation for the phenomenon; it transubstantiates from atautological construct to an essence with causal status (cf.Skinner, 1963). Of course, this is circular, and it is a rarescientist who deliberately engages in circular reasoning.However, it is often easier to ridicule circular reasoningthan to avoid it. William James (1907) noted that al-though no one seriously thinks that wealth is an expla-nation for having money, it is not uncommon to attributesickliness to poor health, or muscular feats to greatstrength, or problem-solving skills to great intelligence.In cognitive science it is not uncommon to attribute lan-guage acquisition to linguistic competence, or ineffectiveperformance on a recall task to limited capacity. Patentlycircular usage is typically avoided by the original pro-ponents of a concept. Circularity often emerges, however,when a concept becomes familiar; it tends to become re-ified, especially by subsequent researchers, students, andwriters of secondary texts. (Indeed, Medin & Ortony,1989, have suggested that such reification may be fun-damental to cognition.)

Curtailment of inquiry. A second shortcoming ofessentialist explanations of phenomena is that they tendto cut off inquiry prematurely (Skinner, 1950). Essentialproperties are treated as givens; they need no further ex-planation. Note that attributing a behavioral phenomenonto an innate structure of the organism is not essentialistic,


for innate structures are presumably selected by evolu-tionary processes. However, the structure will not be ideal,universal, or fixed, but will reveal the variability char-acteristic of all physical features that are the products ofselection. As noted, natural selection permits variabilityand, indeed, may select for variability. Far from beingideal, structures are often opportunistically cobbled to-gether from the available "raw materials" of ancestralspecies (Gould, 1980). Investigating the structure, itsvariability, and its evolutionary origins enriches our un-derstanding of the behavioral phenomenon.

However, the widespread practice of gratuitously in-voking the genetic endowment is essentialism in selec-tionist's garb. To attribute a behavioral phenomenon toan invented property of the organism and then to "ex-plain" the property by casually alluding to the geneticendowment is vacuous unless the origin of the propertycan plausibly be identified and discussed in selectionistterms. The short-term memory register, for example, isa metaphor, not a structure. As a metaphor it may beuseful, but it has no explanatory force, for it is accordedjust those properties necessary to explain the disparatephenomena grouped under the heading short-term mem-ory (cf. Crowder, 1982). To suggest that it is innate is astatement of faith, not a serious proposal. At best, thesuggestion that it is innate is the beginning of inquiry,not its end, for we now have assumed responsibility foraccounting for the natural selection of short-term mem-ory. It is most often treated, not as a variable outcomeof selection, but as a fixed property of the organism. Noattempt is made to treat it as a product of contingenciesof selection.

Unparsimonious explanations. A third drawbackof essentialist concepts, and the last that we shall mentionhere, is that they all require separate explanations. Dar-win's theory achieved a dramatic simplification, as manyapparent acts of creation were shown to be the productof a few common processes, and seemingly unrelatedphenomena were shown to be intimately related to oneanother. Unconstrained by selectionist thinking, thestructures postulated within cognitive science may pro-liferate in an unconstrained manner. For example, whenthe data obtained in memory experiments are not readilyaccommodated by the distinction between short-term andlong-term memory, an intermediate memory may beproposed. Similarly, when not all data obtained with aprocedure used to study long-term memory can be ac-commodated by a single set of processes or structures,different subtypes of long-term memory—semantic versusepisodic or declarative versus nondeclarative—may beproposed. These proposed subdivisions of memory maybegin as convenient shorthand descriptions of observeddifferences but become reified into "types" of memorywhose characteristics are just those required to encompassthe data that were the impetus for their postulation.

Often, such distinctions lead to pointless debate overwhether a given phenomenon is really evidence for a givenconcept or whether it is better taken as evidence of someother concept. For the same reasons that it makes no

sense to ask whether Archaeopteryx is really a bird or areptile, there is little to be gained by asking whether agiven datum in a memory experiment is really fromlong-term rather than short-term memory or from epi-sodic rather than semantic memory. Observations of in-termediate forms and intermediate memories may bothbe of great value because of what they reveal about thecourse of selection, but not because of what they purportto reveal about membership in one or another essentialist"type." Problems with lack of parsimony, as with cir-cularity and curtailment of inquiry, are not necessaryconsequences of assigning names to classes of observa-tions, but they are often the essentialist accompanimentsof such a practice.

Cognitive Science and EssentialismResearchers in cognitive science are seldom explicitly es-sentialistic, of course. However, most cognitive analyseshave, until recently, shown a taste for formal or a prioriunits of analysis and have posited complex, high-levelstructures as explanations of cognitive phenomena, with-out reference to either physical mechanisms explainedby contingencies of natural selection or acquired reper-toires explained by contingencies of reinforcement. Con-sequently, these analyses are implicitly essentialistic, andsubsequently, they come to be treated so by other re-searchers, students, and writers. We will outline severalexamples.

Verbal Behavior

Much of contemporary linguistics, particularly that as-sociated with Noam Chomsky, is an effort to employ es-sentialist analyses to shed light on behavioral phenomena.Here the essentialism is not an inadvertent outcome ofthe careless use of terms but is explicit policy adopted inorder to isolate crucial variables. The goal is not merelyto provide an abstract structural description of languagebut to use that abstract description to tell us somethingabout human beings, how we speak and understand ourlanguage, and how we learn to do so in a few short years.Chomsky (1980a) suggested that an inquiry into languagebe modeled on inquiry into biological systems, such asthe visual system, and that it consider its function, abstractstructure, physical structure, individual development, andevolutionary development (p. 227). Although a completeanalysis of language will include many idiosyncratic phe-nomena, the most interesting questions, in his view, con-cern universal properties of language, particularly thosethat are genetic in origin, for they are "part of an innateendowment that defines the 'human essence' " (p. 92).Chomsky pointed out that "the study of biologically nec-essary properties of language is a part of natural science:its purpose is to determine one aspect of human genetics,namely, the nature of the language faculty" (p. 29).

These biological questions would appeal to any se-lectionist, but the terms abstract structures, language fac-ulty, and human essence all introduce a flavor of essen-tialism. When we look at the realization of Chomsky'sprogram, however, there is no longer any doubt. Citing


methodological and ethical problems in pursuing theother issues mentioned earlier, Chomsky (1965) investedmost of his effort into characterizing the abstract structureof language. He quickly removed to an idealized worldin which everything has essential properties. "Linguistictheory is concerned primarily with an ideal speaker-lis-tener, in a completely homogeneous speech-community,who knows its language perfectly" (p. 3). "I have in mindcertain biological properties that are genetically-deter-mined and characteristic of the human species, which Iassume for the purposes of this discussion to be geneticallyuniform, a further idealization" (Chomsky, 1980a, p. 28)."I have argued that the grammar represented in the mindis a 'real object,' indeed that a person's language shouldbe denned in terms of this grammar" (p. 120). A highlyabstract formal system is proposed. The unit of analysisis assumed a priori: "The basic elements we consider aresentences; the grammar generates mental representationsof their form and meaning" (p. 143). Thus, the sentenceis denned formally, not operationally or empirically. Infact, few, if any of the terms of the analysis can be givenoperational definitions: Chomsky asserted that " 'well-formedness' is a theoretical concept for which we cannotexpect to find a precise set of necessary and sufficientoperational criteria" (p. 198). "Furthermore, there is noreason to expect that reliable operational criteria for thedeeper and more important theoretical notions of lin-guistics (such as 'grammaticalness' and 'paraphrase') willever be forthcoming" (1965, p. 19). Although linguisticintuitions of native speakers play a role in the enterprise,they have limited authority: "In fact, as soon as sentencesbecome moderately complex, judgments begin to waverand often fail, which is neither surprising nor particularlyimportant, but leaves the question of existence of a de-cision procedure wide open" (1980a, p. 121).

Chomsky's approach is avowedly essentialistic; in-deed, he regards an abstract characterization of grammaras the most promising line of inquiry, given the constraintson research with humans. He clearly expects that theanalysis will provide insights into the imperfect and vari-able domain of living organisms where selectionist prin-ciples hold sway, at least in part. Is there any objection,in principle, to this approach? We do not argue so, al-though we regard it as an open question. The Linnaeanclassification of species based on structural features wasessentialistic, and although it is not identical with a systembased on evolutionary considerations, it proved useful inorganizing a bewildering variety of data. However, thetwo classification systems are qualitatively different; theLinnaean system did not contain the seeds of the evo-lutionary one. Selectionist and essentialist units of analysisare incommensurate; the terms in a formal analysis can-not be simply translated into those of an empirical anal-ysis. When our units of analysis are defined formally, asin a grammatical analysis, there is no guarantee that theywill have the orderly properties of units defined empiri-cally. Moreover, if Chomsky was correct that many gram-matical concepts cannot be given operational definitions,the translation becomes even more formidable, if not im-

possible. We believe that this point is insufficiently ap-preciated by Chomsky and his followers.

We question, for example, that the sentence is anappropriate unit of analysis. In a formal system, sentencesare defined by a grammar, and grammars, at least thoseproposed for human languages, can generate an infinitenumber of sentences. Given a finite vocabulary, it is ob-vious that only an infinitesimal fraction of these infinitesentences would have fewer than, say, a billion words.This imperfect fit between the sentences generated by theformal system and actual units of behavior is dismissedby Chomsky as simply reflecting the difference betweencompetence and performance. Similarly, performancevariables are invoked to explain the fact that people oftendo not speak in sentences and the fact that grammaticalintuitions are notoriously fickle. It seems to us that thecompetence-performance distinction is being used tomask the fundamental variability of behavior in order toshore up the formal edifice. The sentence is the preferredunit because it permits a formal analysis, not because itis an orderly unit of behavior.

Second, we question the device of characterizinglanguage abstractly and then imputing the formal edificeto the organism as part of its innate endowment. It istaken for granted by Chomsky and his colleagues thatpeople use a grammar when speaking and listening. Lin-guists have found it to be a difficult matter to provide afully adequate grammar for natural languages; no doubtthere seems to be no alternative to assuming that peopleactually use such a system. However, there is no force tothis conclusion. A child can learn to catch a baseballpresumably because of the orderliness of the laws of mo-tion, but we do not assume that the child has inducedthese laws. The possibility cannot be rejected, but untilthe account is fleshed out in biological terms, imputingformal laws to the child as an explanation of his behavioris circular.

Chomsky attempted to embed his formal systemwithin the natural sciences by arguing that he was pro-viding an abstract characterization of properties of thegenome. His formal analysis of language reveals manyregularities that can be described by abstract rules. Noone teaches these rules to children, and no one consciouslyuses them when speaking or writing. Some rules facilitatecommunication, and one might argue that they arelearned as a consequence of communicative contingen-cies. Many of the rules, however, are wholly arbitrary;utterances would be reasonably intelligible if the rule wereviolated. Chomsky (1975) pointed out that, for somerules, it is unlikely that many people have had experiencethat even bears on the rule; indeed, "it is often a difficultproblem even to discover examples that bear on the hy-pothesis in question" (p. 175). In other cases, inductionfrom personal experience would suggest violations of therule, violations that are not, in fact, observed. Chomsky(1980a) argued,The knowledge acquired and to a large extent shared involvesjudgments of extraordinary delicacy and detail. The argumentfrom poverty of the stimulus leaves us no reasonable alternative


but to suppose that these properties are somehow determinedin universal grammar, as part of the genotype. There is simplyno evidence available to the language learner to fix them, inmany crucial cases that have been studied, (p. 66)

This argument has a superficial cogency. In ourpresent understanding of biology, if a characteristic cannothave been acquired, we assume that it is genetic in origin.However, as has been noted, learning principles and evo-lutionary principles are parallel selectionist principles.Both account for complex phenomena by appealing tovariation, selection, and retention. The same evidencethat is adduced to argue that a rule cannot have beenlearned can be used to argue that it cannot have evolvedthrough natural selection. Arbitrary rules that have nocommunicative or practical consequences cannot confera selective advantage to an individual who uses such rules.If it is hard even to find examples that bear on the issues,it is unlikely that the grammatical distinctions will con-tribute to evolutionary fitness. Acknowledging this dif-ficulty, Chomsky (1980b) argued that although the childmust learn his language in a few years, evolution has hadmany thousands of years to select universal grammar.However, the length of time that selection is at work isirrelevant if the grammatical distinctions are arbitrary.The "argument from poverty of the stimulus" applies toany selectionist account, be it ontogenetic or phylogenetic.Attributing a complex phenomenon to the genetic en-dowment without requiring that the evolutionary accountbe plausible, or even possible, is comparable to arguingfor the special creation of species.

The conclusions that Chomsky (1969) drew fromhis formal analyses appear inconsistent with principlesof selection. Rather than question the analyses, Chomskypreferred to question selectionism:

It is, in fact, perfectly possible that the innate structure of mindis determined by principles of organization, by physical con-ditions, even by physical laws that are now quite unknown, andthat such notions as "random mutation" and "natural selection"are as much a cover for ignorance as the somewhat analogousnotions of "trial and error," "conditioning," "reinforcement,"and "association." (p. 262)

In this appeal to additional but unknown principles,even to "physical laws. . . now quite unknown," Chom-sky (1969, p. 262) explicitly cast himself loose from theselectionist principles that unify the biological sciencesand that provide an explanation for diversity and com-plexity at both the ontogenetic and phylogenetic levels.The retreat to an ideal, essentialist world is no longer atemporary recourse but an end in itself.

Not all linguists are equally dismissive of the needto provide a selectionist interpretation of linguistic anal-yses. Pinker and Bloom (1990) noted, "If a current theoryof language is truly incompatible with the neo-Darwiniantheory of evolution, one could hardly blame someone forconcluding that it is not the theory of evolution that mustbe abandoned but the theory of language" (p. 708). Theythen provided a masterful interpretation of the adaptive-ness of human language. Their account succeeds admir-

ably in relating the facts of language to selectionist theory,but it falls short of showing that an essentialist interpre-tation of these facts is justified. As Hornstein (1990) asked,

What evolutionary pressure selects for the case filter or structuredependence or the binding theory or X' theory? It seems at firstblush that a perfectly serviceable communication system thatdid not mark "abstract" case on [noun phrases] could be justas good a medium of communication as one that does. (pp.735-736)

The force of Pinker and Bloom's argument rests on thelack of a precise alternative account for the grammaticalregularities they discussed. However, we argue next thatformal models in linguistics do not themselves provideexplanations of these regularities.

Chomsky holds that humans are endowed with aninnate device that will generate a grammar appropriateto their speech community, based on a limited set of ex-emplars. Even with impoverished input, a child will mas-ter grammatical distinctions and so avoid errors thatmight be suggested by induction from the exemplars. Thisappears to be a reasonable proposal until we ask howsuch a device would work. There are many examples ofbehavior that are evidently largely genetic in origin (e.g.,courtship rituals, maternal behavior, warning cries, feed-ing). In each case it is possible to identify the propertiesof the class of stimuli that elicits the behavior. Often it ispossible to "trick" the organism by exposing it to super-normal stimuli or inappropriate stimuli within the class,as when a duckling is imprinted on a human or a hawk.In the case of Chomsky's putative generator of grammars,however, there is no way to characterize the input to thedevice; the input is entirely arbitrary. A child in Francewill be exposed to French, the child in Cuba will be ex-posed to Spanish, and the deaf child will be exposed tosigning. An innate mechanism can make no use of sucharbitrary inputs. In order for such a device to be possible,the inputs to the device must already be segmented andanalyzed into phrases, words, and parts of speech. Herewe are faced with the familiar problem that such termsare essentialistic; they have meaning only in the world offormal analysis, not in the world of fundamentally vari-able classes of environmental and behavioral events. Thegrammatical classes of the formal analysis cannot be de-fined in terms of such events; neither, according toChomsky, can they be operationally defined. Rather thansolving the child's problems, Chomsky's proposal seemsto raise new ones that have no solution.

This objection is often countered by the suggestionthat the child acquires knowledge of grammatical classesby a kind of "bootstrapping" operation (e.g. Grimshaw,1981; Pinker, 1982, 1984). Nouns are often uttered inthe presence of "things," and verbs in the presence of"actions." Through interacting with the world and withproficient speakers, the child learns such distinctions andrefines them with further experience. Once armed witha modest repertoire of word-concept pairs, the child setsto work analyzing patterns in the sentences he or shehears. Through this sort of distributional analysis the child


can generalize to abstract nouns and verbs and can iden-tify determiners, suffixes, and so on.

Such proposals do not specify how this bootstrappingoperation actually works, for the formal conceptual ap-paratus of linguistics is not equipped to analyze environ-mental and behavioral classes of events. What, specifically,are the stimulus properties of a "thing"? When is a stim-ulus a thing, as opposed to an attribute? What eventsentail reference, as opposed to coincidence? It is not suf-ficient to allude to the child's knowledge of such things,for that merely rephrases the mystery; we need an analysisof what happens at the level of stimulus input to the or-ganism without taking refuge in the child's "knowledge"or "concepts." Finally, exactly how does the nonverbalchild conduct the elaborate hypothesis testing necessaryto conduct a distributional analysis of language? As Pinker(1984) himself observed, "If the theory is correct, then Ihave placed a considerable burden on theorists of con-ceptual and communicative development, saddling themwith an inventory of cognitive abilities far richer thanmany current cognitive theories allow for" (p. 362). Tous, the proposed solution seems as formidable a problemas the original mystery.

We do not doubt that a child learns his or her lan-guage through the kinds of interactions implied by thesemantic bootstrapping hypothesis, but we question thathe or she will learn the essentialist concepts of Chomskianlinguistics. What a child learns from such interactionsare not grammatical terms but, curiously enough, thebehavioral units analyzed by Skinner (1957) in VerbalBehavior. Skinner's account avoids these problems be-cause his generic units are perfectly suited to the analysisof inherently variable environment-behavior interactions.If Chomsky's proposals are to find a place in contem-porary biological thought, they must eventually be trans-lated into selectionist terms; when they are, it will befound that Skinner got there first.

We have argued that Chomskian linguistics, one ofthe most important themes in contemporary cognitivescience, is heavily essentialistic and, for just that reason,promises little help in integrating cognitive science withthe rest of biology (cf. Andresen, 1990; Palmer, 1986).Chomsky (1959) has explicitly rejected an account oflanguage in terms of reinforcement contingencies, and aswe have indicated, the mechanisms he proposed as analternative seem to be immune to contingencies of naturalselection. Moreover, Chomsky has not shown how totranslate his formal apparatus into the biological worldwith its fuzzy boundaries and permissive contingenciesof selection. His proposed innate mechanisms, in solvingone problem for the organism, pose new problems thatto us seem insuperable.

Remembering

Other examples of essentialist thinking in cognitive sci-ence can be found in conventional views of memory.Memories are seen as things, things that are stored, thingsthat are retrieved, and things that can explain subsequentbehavior (cf. Watkins, 1990). We learn on Tuesday that

a man's name is Johnson; on Wednesday we hail him byname. Within cognitive science, it is conventional to saythat the man's name was stored as a memory and wasretrieved the following day. The storage metaphor—ametaphor that is accepted uncritically by nearly everyonein cognitive science—supports this view of memory; tostore is a transitive verb, and that which gets stored mustbe a thing. On different occasions we hail Johnson byname, we picture his face, we write him a note. Thememory is not seen as the utterance, the image, or thescrawl; rather, the memory is seen as a unitary thing un-derlying the various behavioral manifestations, just as, toan essentialist, the species is a prototype of which indi-viduals are imperfect manifestations.

Few scientists take the storage metaphor literally;the brain is a memory storehouse only in a figurativesense. Certainly the nervous system changes with expe-rience, and these changes may endure, but it is not thesechanges that we speak of when we speak of memories.We do not retrieve synaptic changes when we "retrieve"a memory. We suspect that the more the physiologicalbases of learning are understood, the less compelling thestorage metaphor will be. We are not tempted to say thatthe patellar reflex is stored in the spinal cord. A reflex isa relationship between a class of stimuli and a class ofresponses; apart from this relationship it does not exist.When we identify a neural pathway, a "reflex arc," wehave not isolated a reflex; we have just shown how itworks. Similarly, memories have no existence apart froma relationship between those conditions that evoke themand the various behavioral outcomes from which mem-ories are inferred. The underlying physiology is a pathway(or a network of pathways), not an essence.

Even though few take the storage metaphor literally,it appears to guide much theorizing in the field. Semanticnetwork models and structural models of every sortsubscribe to it, and the impact of these models has beentremendous. Difficulties with the Atkinson-Shiffrinmodel may be apparent to memory theorists, but theconcepts of the model pervade the thinking of cognitivescientists and laymen alike. For a selectionist, however,questions about memory are most generally conceived asproblems in stimulus control: What are the conditionsunder which present behavior is affected by selection byreinforcement of behavior in prior environments? Incontrast, within most of cognitive science, rememberingis approached as a set of problems in storage, search, andretrieval. From the selectionist perspective, an instanceof recall is an instance of current behavior (some of whichis possibly covert) and should be investigated just as anyother instance of behavior. The antecedents of a memoryare often much more complex and difficult to observethan the antecedents of an eyeblink, but a difference incomplexity is not a difference in kind. In a recall task wesearch not for memory traces but for controlling stimuli(often response produced). The resulting behavior is aunique event; although it may be, and usually is, a mem-ber of a response class, a response does not represent orstand for other responses. All behavior is equally a product


of current controlling variables. From a selectionist's pointof view, just as a given morphological feature can havedifferent evolutionary histories in different organisms, aresponse of a given topography can have many anteced-ents, even in a single organism. In a recall task, a responseof a particular topography is said to be "correct," re-gardless of the antecedents of the response. The storagemetaphor is misleading in that it suggests that the responseis not the product of a unique confluence of current eventsbut of an invariant, hidden, surrogate of behavior.

A selectionist view draws our attention to the roleof current variables and asks how they can account formemory phenomena. It is evident that some instances ofrecall are the direct outcome of past selections. When wefumble for the windshield-wiper switch of an unfamiliarcar, we twist knobs and pull levers until the wipers go on.On the next occasion, we may reach for the correct switchimmediately. Similarly, we may respond "1588" whenasked "When was the Spanish Armada?" because thatresponse to the question was reinforced in grammarschool. However, many memory phenomena require amore elaborate interpretation. When asked, "Where wereyou last Thursday?" we do not reply with a stock answerthat was reinforced in the past. When asked such a ques-tion we engage in recall strategies that supplement currentcontrolling variables with those that are generated by ourown responses: "Let's see . . . today's Monday. . . . OnWednesdays I have Historical Society meetings. . . . Istayed out late Wednesday night. . . . I must have stayedin bed late on Thursday," and so on. The question doesnot directly evoke the response; rather, it initiates an ac-quired procedure of generating responses that, togetherwith the initial question, may or may not be adequate tocontrol the "answer." Thus, whether or not a response isdirectly controlled by a stimulus, we attempt to analyzememory phenomena as current behavior under controlof current variables, using units of analysis consistent withSkinner's formulation. (See Donahoe & Palmer, in press;Palmer, 1991, for a more extensive discussion of thesepoints.)

We are not suggesting that all findings that are ob-tained in research guided by the storage metaphor arewithout merit. Researchers, regardless of their theoreticalcommitments, are constrained to investigate manipulableindependent variables, not memory traces, and much ofthe resulting body of data is important, regardless of one'sperspective. However, we believe that most theories ofmemory, to the extent that they are essentialistic, are mis-leading and contribute little to the value of research inthe field.

Representation

A third manifestation of essentialism within cognitivescience, one that seems to reach into all corners of thefield, is that of representation. A representation is morethan a copy; it is a symbol, capable of being stored, ma-nipulated, and transformed. The thing being repre-sented—usually some stimulus, event, or action—me-tamorphoses from a unique environment-organism re-

lationship into an abstraction, an ideal, and in so doingcrosses the boundary into the essentialist domain of for-mal analysis. The effect of this transubstantiation froman event in the physical world to an abstraction in anessentialist world of representation may sometimes beharmless, but it is all too easy to forget that one has madean idealization and, then, to ask questions that make senseonly in the world of symbols, not in the world of stimulusand response classes. We are particularly apt to do sowhen discussing meaning and reference. Nothing is morenatural than to ask the meaning of a word or sentence,as if meaning were a property of an utterance, independentof an individual speaker or listener.

When spoken, a verbal expression is a response, tobe understood as a product of the current situation, theorganism, and a particular selection history. We may bereading the expression from a book, solving an anagram,repeating what someone else has said, alerting our listenerto some state of affairs, recalling an anecdote, reciting afamous quotation. We provide a meaning of the utteranceby considering such variables, along with the past expe-rience of the speaker; the topography of the response neednot be considered. For the listener, bringing a differenthistory to bear, the meaning is different. For him, theutterance is not a response but a stimulus, and meaningis to be sought partly in his experience with elements ofthe class exemplified by that stimulus.

Perhaps it is just because utterances of a particulartopography can have so many diverse origins that we striveto attach meaning to the elements themselves, somethingthat will transcend the idiosyncratic instance. There is atypical, or modal, circumstance in which a typical speakermight emit such an utterance, and meaning is distilledfrom these considerations. Superficially, this view appearsto simplify matters considerably. Meaning, as a propertyof a word (either as stimulus or response) becomes com-mon to speaker and listener, in fact, to the entire verbalcommunity. This notion of meaning is useful in everydayaffairs; we ask "What does that mean?" when confused,and we would be quite lost without dictionaries. Verbalbehavior would appear to be pointless unless there weresomething common to speaker and listener, and the termmeaning seems to capture that common element.

However, when we analyze the behavior of a singlespeaker or listener in terms of contingencies of selectionthe term meaning does not appear, just as the term speciesdoes not appear in an analysis of a morphological featurein an individual organism. The term meaning dissolvesinto myriad experiences of the individual just as a mor-phological feature is the product of countless unique in-stances of variation and selection (cf. Skinner, 1957, pp.7-10). The simplification achieved by treating meaningas a property of a stimulus may be useful in casual dis-course, but it can cost us dearly if we take it seriously,that is, if we use an essentialist concept such as meaningto guide our theories about the products of selection (i.e.,about organisms). Yet, the notion that words and phraseshave meaning is central to semantic network models,models with lexicons, and computerized translation al-


gorithms, and it is suffused throughout most analyses oflanguage and intelligence.

Research guided by essentialist views of meaningand reference typically presents subjects with contrivedstrings of words, usually written, and tests recall, recog-nition, reaction time to answer questions, and so on, inan attempt to determine the components of concepts, theconstituent structure of propositions, the system of storageof semantic units, and to distinguish between the predicatetheory and the case theory of propositions—and so on.Implicit in this approach is the view that meaning is aproperty of a string of words, independent of the historyof our subjects. From a selectionist view, such experimentstell us only about the typical verbal practice of the com-munity from which the subjects were recruited. There isno general truth, no fact of the matter to be discovered.A string of words drawn from a hat, or carefully con-structed by an experimenter to serve as a stimulus, hasno meaning whatever. Once presented to a subject, thestring has a meaning in the sense that it has an effect onthe subject, just as a tone might have a meaning to alaboratory rat. But the meaning of the string, like themeaning of the tone, is a product of the history of thesubject, not an intrinsic property of the stimulus. Mostof our subjects are sophisticated enough to pretend thatthe stimulus string was generated by someone respondingto a real state of affairs; the generality of such experimentsdepends on such dubious inferences.

Verbal communities maintain common contingen-cies so that most members respond in similar ways togiven verbal stimuli. The uniformity and universality ofthese contingencies provide the order that we try to cap-ture when we speak of meaning or reference. However,as noted above, such contingencies can be satisfied inmany idiosyncratic ways. As we have said, contingenciesof selection, be they contingencies of reinforcement orcontingencies of natural selection, do not yield classeswith essential properties. We may mask this variabilityby averaging our data, but such variability is not error;it is an unavoidable and important outcome of the pro-cesses of selection. It is the variant, not the mean, that ismost profitably examined, for selection operates on in-dividuals or elements, not on means.

Essentialism in Other Areas of PsychologyThe tendency to slip into essentialist modes of thinkingis not confined to one perspective in psychology. Theavowed essentialist is rare within any theoretical tradition,but even the most committed selectionist finds it difficultto avoid reifying distinctions once they have been named.

Behavior Analysis

We have claimed that radical behaviorism is the mostthoroughgoing selectionist approach within psychology.One of the central distinctions of that approach is theoperant-respondent distinction, which captures the gen-eralization that some response systems, toward one endof a continuum, are narrowly committed to particularfunctions and are recruited only by specific stimuli or

their antecedents, whereas other response systems, towardthe other end of the continuum, are virtually uncon-strained in their potential interactions with the environ-ment. Accordingly, two different experimental proce-dures, the operant and classical conditioning procedures,must be used to investigate the full range of relationsbetween the environment and behavior that may be se-lected by reinforcers. The experimental proceduresthemselves have defining properties, specified a priori bythe canons of the paradigm. The procedures, then, likedodecahedrons, have essential properties.

It does not follow, however, that the responses studiedwith the operant and classical procedures have essentialproperties (i.e., that operants and respondents are twodifferent types of responses requiring two different typesof conditioning principles for their description). And yet,it is not uncommon to find such distinctions debatedwithin the technical literature and generally acceptedwithin the secondary literature. Indeed, textbooks onlearning often classify responses as operant or respondent,independent of procedural considerations, as if they dif-fered in some essential quality of "operancy." For ex-ample, it is sometimes asked if a particular response is"really" a respondent, or if a particular event is not"really" an eliciting stimulus rather than a discriminativestimulus. None of this is to say that the operant-respon-dent distinction is not a critically important one for manypurposes, but that the distinction can lend itself to essen-tialist misinterpretations (Donahoe, Millard, Crowley, &Stickney, 1982).

Another distinction within the radical-behavioraltradition that lends itself to essentialist interpretation isthe distinction between contingency-shaped and rule-governed behavior (Skinner, 1966a). Contingency-shapedbehavior is most immediately understood in terms of itsprior consequences; rule-governed behavior is most im-mediately understood in terms of verbal, contingency-specifying antecedents (Cerutti, 1989; Schlinger & Blakely,1987). Thus, a person who ingratiates him or herself withanother by listening attentively to his or her conversationmay be doing so because, in the past, such behavior hasbeen reinforced with social reinforcers provided by theother person. Alternatively, attentive listening may be theresult of just having taken a Dale Carnegie course on"how to win friends and influence people." Behavior ofthe same topography—attentive listening—can be re-garded as contingency shaped in the first instance andrule governed in the second.

The distinction between contingency-shaped andrule-governed behavior exemplifies one of Skinner's mostimportant contributions—the rejection of topography ofresponse as a sufficient defining variable in the study ofbehavior. As illustrated in the preceding example, a re-sponse of the same topography may be brought about bymany different means—through social and nonsocialcontingencies, through imitation of others, or—in indi-viduals with appropriate histories—through the effect ofinstructions on behavior. When we first sit down at acomputer, a phonograph, or an automobile, our behavior


is guided almost entirely by instructions; with practice,natural contingencies exert their effects. Although be-havior on the two occasions may be topographically sim-ilar, important differences remain, differences that canbe attributed to the shaping contingencies.

The distinction between rule-governed behavior andcontingency-shaped behavior arose from these consid-erations, and the labels are frequently helpful. However,contrary to the spirit of the original distinction, the termsare sometimes used as if the distinction lay in the behavioritself, as if there were two different types of behavior. Forexample, rule-governed behavior, we are told, may be lesssensitive to its consequences than contingency-shapedbehavior. The data underlying this conjecture (e.g., Mat-thews, Shimoff, Catania, & Sagvolden, 1977) are of in-disputable importance, but the essentialist cast of the in-terpretation of the different effects of reinforcers on re-sponses of these two origins is unhelpful. It obscures thefact that rule-governed behavior is itself the product ofprior selection by its consequences. If the essentialist toneof the distinction between contingency-shaped and rule-governed behavior persists, we should not be too surprisedto find a controversy emerge over whether a particularbehavior, shown to be sensitive to its consequences, is"really" rule governed.

Associationism

The other major noncognitive alternative to understand-ing behavior is associationism. Although there are manyselectionist aspects to associationism, one distinction—that between learning and performance—is often redolentof essentialism in modern versions of associationism.When the observed relation between the environment andbehavior is not as orderly as the experimenter might wish,the irregularity is often attributed to perturbations of anunderlying order—learning—by processes of a differenttype—those affected by performance variables. The per-formance variables are thought to obscure the underlying,idealized process much as they are said to do in the formalanalysis of syntax. Although the learning-performancedistinction reflects an important insight, notably that al-most every instance of behavior is a function of manyvariables, to attribute invariant, thing-like properties tothe effects of some of those variables and to deny themto others is akin to attributing some of the characteristicsof an organism to its species and others to different typesof constructs (e.g., varieties and individual differences;cf. Skinner, 1950; see Donahoe, 1984, for other commentson essentialism within the associationist approach).

Connectionism and SelectionismAlthough no domain in psychological science seems tobe entirely free of essentialist analyses, we detect a wel-come selectionist trend in some recent work. Evolutionaryepistemology, ethology, and radical behaviorism have al-ways been avowedly selectionist, of course, but the recentresurgence of interest in connectionism, or parallel dis-tributed processing, is a conspicuous example of a shiftof emphasis away from essentialism in cognitive science.

Connectionist models attempt to simulate complexbehavior by means of adaptive networks made up of sim-ple processing units, loosely analogous to neurons. Thestrength of interconnections among units, which deter-mine the input-output relations that the network cansimulate, are often modified by some feedback mecha-nism (Rumelhart, Hinton, & Williams, 1986). The feed-back mechanism that supervises learning has the effectof selecting successful patterns of activation of the path-ways in the network. Part of the appeal of adaptive net-works lies in their power and their parsimony: Complexoperations can be performed by the repeated action ofrelatively primitive processes. An equally important partof their appeal arises from the fact that the analogy withthe nervous system is plausible enough to encourage thehope of a profitable interdisciplinary attack on the prob-lems of complex human behavior (Smolensky, 1988). In-deed, many proponents of adaptive-network models arebiologists hoping to simulate the activity of portions ofthe nervous system (e.g., Edelman, 1987). Some regretthat adaptive-network models are not more closely guidedby neurophysiological and neuroanatomical data (e.g.,Crick & Asanuma, 1986; Minsky & Papert, 1988), andneural plausibility will surely emerge as one criterion forevaluating such models. Insofar as these models simulatebiological processes, that is, insofar as they are informedby experimental analyses of physiology and behavior, theyare likely to be consistent with selectionism rather thanessentialism (cf. Trehub, 1991).

Three features of adaptive networks are fundamentalto their implementation of a selectionist account of com-plex behavior (Donahoe, 1991). First, a criterion output,given a particular input, can generally be achieved by anindefinite number of different combinations of activatedpathways. Second, the terminal topography of the outputis the product of a particular sequence of selections bythe feedback mechanism. Third, although the initial stateof the network may affect the speed with which a criterionoutput is achieved, given particular feedback contingen-cies, a wide variety of initial states will all evolve intonetworks that mediate the criterion input-output func-tion. Taken together, these features reduce the likelihoodthat adaptive-network models will be given essentialistinterpretations. The criterion output is not dependent onany one pattern of activated pathways (representations),the pattern of activated pathways that produces the cri-terion output pattern differs with different selection his-tories, and the selection history—which reflects thestructure of the environment—determines the pattern ofactivated pathways more importantly than does the initialstructure of the network (cf. Norman, 1986).

Because the input-output relations mediated byadaptive networks are not the product of invariant, un-derlying, idealized structures within the network, one isless tempted to scrutinize a network for units (nodes) orpatterns of activation that can be labeled memories, en-grams, images, meanings, or rules—entities that arecommonplace in the metaphorical models of traditionalcognitive theories. In general, there is no one unit or pat-


tern of activity within the network that corresponds toany of these constructs. To quote Rumelhart and Mc-Clelland (1986), "Many of the constructs of macroleveldescriptions such as schemata, prototypes, rules, pro-ductions, etc. can be viewed as emerging out of interac-tions of the microstructure of distributed models" (p.125). And in the same vein:

Schemata are not things. There is no representational objectwhich is a schema. Rather, schemata emerge at the momentthey are needed from the interaction of large numbers of muchsimpler elements all working in concert with one another. . . .In the conventional story, schemata are stored in memory.. . .In our case, nothing stored corresponds very closely to a schema.What is stored is a set of connection weights which, when ac-tivated, . . . generate states that correspond to instantiatedschemata. (Rumelhart, Smolensky, McClelland, & Hinton,1986, pp. 20-21)

The fact that our microstructural models can account for manyof the facts about the representation of general and specific in-formation . . . makes us ask why we should view constructslike logogens, prototypes, and schemata as anything other thanconvenient approximate descriptions. (Rumelhart & Mc-Clelland, 1986, p. 127)

Clearly, adaptive network models do not encourage es-sentialist interpretations.

Essentialist Temptations Within Connectionism

Most adaptive-network researchers pursue their work withlittle, if any, regard for the essentialism-selectionism issue.Nevertheless, most such models instantiate the three se-lectionist steps to complexity: variation, selection, andretention. The state of the network is in constant flux,patterns of activation that mediate criterion outputs arestrengthened, and successful pathways are preserved asstable connection weights between units in the network.

Although adaptive networks provide a theoreticalframework within cognitive science that is congenial tothe selectionist approach to complexity, there are severalpoints at which temptations to essentialism exist. As isthe case with other selectionist approaches, such as radicalbehaviorism, adaptive-network theory does not conferimmunity to the charms of essentialism. Only two suchenticements are mentioned here—the search for simplecorrespondences between the nodes and pathways of thenetwork and verbally characterized cognitive processes,and the effort to endow the feedback mechanisms thatselect the connections with essentialist properties.

Verbal characterization of adaptive networks. Asmentioned earlier, in an adaptive network no simple re-lation exists between the units or patterns of activity andany normative cognitive construct. More precisely, thereis, in general, little correspondence between our verbaldescriptions of the activity of specific elements of the net-work and our verbal description of the cognitive processesthat we observe in ourselves and infer in our subjects.The patterns of activity within the network specify ourverbal descriptions (Gibson, 1979) in the sense that theyconstitute sufficient conditions for the descriptions, but

their dimensions are incommensurate with those of theverbal description. Minsky and Papert (1988) made thepoint this way:

It is because our brains primarily exploit [adaptive networks]that we possess such small degrees of consciousness, in the sensethat we have so little insight into the nature of our own con-ceptual machinery.. . . What appear to us to be direct insightsinto ourselves must be rarely genuine and usually conjectural,(p. 280)

In spite of the absence, in general, of a one-to-onecorrespondence between network elements and cognitiveconstructs, we may anticipate continued efforts to identifysuch simple correspondences. Furthermore, because someapparent correspondences may indeed be occasionallyfound, such efforts are likely to persist for some time. Itmust be appreciated, however, that even when corre-spondences are identified, they are most likely to be con-stituents of transient patterns of neural activity ratherthan enduring essentialist entities. For example, one mayfind in the brain of a sheep a cell whose firing is highlycorrelated with the presence of the complex constellationof stimuli provided by faces of other sheep (Kendrick &Baldwin, 1987). Nevertheless, that cell is best interpretednot as an abstract representation offace, but as a cell thatis only one element of a network of neural activity reliablyactivated by the complex stimuli provided by faces (and,perhaps, other objects as well). The selectionist origin offace cells is revealed in the finding that face cells in sheepdo not respond to inverted faces of sheep, whereas monkeyface cells do correspond to their inverted counterparts(Kendrick & Baldwin, 1987). Monkeys have a selectionhistory that includes the inverted faces of conspecifics;sheep do not.

Nature of feedback mechanisms. Feedback mech-anisms in adaptive-network theory serve to modify thestrength of connections so that a given input from theenvironment will cause a given output to occur from thenetwork. Various versions of adaptive network theory usedifferent feedback mechanisms, and some of these feed-back mechanisms have essentialist characteristics. Forexample, one commonly used mechanism, the delta rule(Rumelhart, Hinton, & Williams, 1986), requires thatthe correct output pattern be known from the beginningof training so that differences between the obtained outputon a trial and the ideal output may be fed back to thenetwork. Such a feedback mechanism is essentialistic inthat it assumes that which must be discovered by thelearner—the correct response. Feedback rules of this formare both regrettable and unnecessary. They are regrettablein that they introduce an element of teleology: The net-work must know in advance what the ideal output shouldbe. They are unnecessary in that a feedback mechanismthat does not make such an assumption and that is con-sistent with the behavioral and neurophysiological analysisof reinforcement is sufficient (cf. Donahoe & Palmer,1989; Donahoe et al., in press; Sutton & Barto, 1981;Widrow & Hoff, 1960). In summary, the emergence ofparallel distributed processing admits a selectionist ap-


proach within cognitive science, but, as with radical be-haviorism, it does not ensure that a selectionist interpre-tation will be consistently adopted.

SummaryContingencies of selection are capable of yielding orderlyclasses of complex phenomena, and these classes may bestable so long as the contingencies remain stable. However,selection contingencies merely set limits on class mem-bership; they do not provide blueprints. Elements withinclasses will vary within these limits, constrained only bythose mechanisms that generate variability in the firstplace. If the duration of our observations is small relativeto the duration of the contingencies, such classes mayseem to have essential properties. In any case, once classesare named, the fundamental variability of all productsof selection is obscured.

Skinner was perhaps unique within psychology incorrectly grasping the variable nature of his subject matterand specifying an appropriate methodology. In doing sohe wove his science seamlessly into the fabric of modernbiology, permitting interpretations of behavior that draw,with equal facility, from ontogenetic and phylogeneticcontingencies. In contrast, many contemporary cognitivescientists celebrate their freedom from behaviorist meth-odological constraints mindless, apparently, of the reasonsfor heeding these constraints. To the extent that theiranalyses are implicitly essentialistic, their science is dis-continuous with biology. Although recent practice in vir-tually all areas of psychology reveals examples of essen-tialist thinking, current interest among cognitive scientistsin adaptive networks and the current interest among lin-guists in natural selection suggest a trend that may ulti-mately yield a selectionist theme that unifies cognitivescience and permits a fruitful dialogue with radical be-haviorism.

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