Evolutionary Psychology Explained

 

Evolutionary Psychology Controversies, Questions, Prospects, and Limitations Jaime C. Confer, Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis, Carin Perilloux, and David M. Buss University of Texas at Austin

 Evolutionary psychology has emerged over the past 15  years as a major theoretical perspective, generating an increa inc reasin sing g vol volume ume of emp empiri irical cal stu studie diess and ass assumi uming ng a larger presence within psychological science. At the same time, it has generated critiques and remains controversial among some psych psychologis ologists. ts. Some of the contr controvers oversyy stems  from hypotheses that go against traditional psychological theories; some from empirical findings that may have disturbing turbin g implic implications ations;; some from misund misunderst erstanding andingss about  the logic of evolutionary psychology; and some from reasonabl son ablee sci scient entific ific con concer cerns ns abo about ut its und underl erlyin ying g fra framemework. wor k. This article article ide identifi ntifies es som somee of the most com common mon concerns and attempts to elucidate evolutionary psychology’s sta gy’s stance nce per pertai tainin ning g to the them. m. The These se inc includ ludee iss issues ues of  testability and falsifiability; the domain specificity versus domain generality of psychological mechanisms; the role of novel environments as they interact with evolved psychologi cho logical cal cir circui cuits; ts; the rol rolee of gen genes es in the con concep ceptua tuall structure of evolutionary psychology; the roles of learning, socialization, and culture in evolutionary psychology; and  the practical value of applied evolutionary psychology. The articl art iclee con conclu cludes des wit with h a dis discus cussio sion n of the lim limita itatio tions ns of  current evolutionary psychology. Keywords:  evolutionary psychology, misconceptions, ad-

aptation, psychological mechanisms, natural selection he goal goal of evol evolutio utionary nary psychology psychology is to stud study y

Theoretical Background The fundamental basis of evolutionary psychology dates back to Darwin’s (1859) theory of natural selection. Darwin postulated that if variant traits could be inherited by offspring from parents, then those variants that aided an organism’s survival and reproduction would be transmitted to future generations at greater frequencies than alternatives. Variants with less beneficial effects—such as those that hinder an organism’s ability to survive or reproduce— would not replicate because the organisms possessing them would transmit them at lower rates. This causal process results in three products: (a)  adaptations,1 inherited characteristics that reliably solved problems related to survival and reproduction better than competing alternatives during the time period in which they evolved (example: fear of  dangerous snakes); (b) by-products, artifacts without functional value that persist because they are inherently coupled with adaptations (example: fear of harmless snakes); and (c)  noise, variations in a given characteristic that are due to random environmental events or genetic mutations (example: random low base-rate fears, such as fear of sunlight, that occur because of stochastic genetic or developmental factors) (Tooby & Cosmides, 1992). Although these principles historically have been applied to anatomy and physiology, there is now widespread recognition that they also provide powerful tools for explaining the origins of psychological, strategic, and behavioral adaptations in nonhuman animals as well as in hu-

human behavior as the product of evolved psychological mechanisms that depend on internal and environmental environment al input for their developme development, nt, activation, and expression in manifest behavior. Although empirical resea res earch rch wit within hin evo evolut lution ionary ary psy psycho cholog logy y has gro grown wn stead ste adily ily ove overr the pa past st 15 yea years rs (Co (Cornw rnwell ell,, Pal Palmer mer,, Guinther, & Davis, 2005), some within mainstream psychology chol ogy rema remain in unfa unfamilia miliarr with its theo theoreti retical cal fram frameework and application, and misconceptions about it are common (e.g., Cornwell et al., 2005; Park, 2007). The purpose of this article is to clarify some of the tenets of  evolutionary psychology and to dispel several common misconceptions about it. By doing so, we hope to provide some conceptual tools to facilitate a greater integration grat ion of evol evolutio utionary nary psyc psycholo hology gy with main mainstre stream am

man mans s ations (Alcoc (Al cock, k, 200 2005; 5; Bus Buss, 2005). 200 5). Just t asiated physio phy siolog logica icall adaptations adapt solve specific speci fic s,proble problems ms Jus associated assoc with surviva vi vall an and d re repr prod oduc ucti tion on (e (e.g .g., ., th thee im immu mune ne sy syst stem em ha hass evolved as a defense against disease), psychological adaptation tat ionss too hav havee evo evolve lved d bec becaus ausee the they y sol solved ved pro proble blems ms related to survival and reproduction (e.g., preferences for

psychological theory and research.

time they appear.

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Jaime C. Confer, Judith A. Easton, Diana S. Fleischman, Cari D. Goetz, David M. G. Lewis Lewis,, Carin Perilloux, Perilloux, and David M. Buss, Department Department of  Psychology, University of Texas at Austin. We thank Laith Al-Shawaf, Matthew Brooks, Meg Cason, Aaron T. Goetz, Owen Jones, William Swann, and Yla Tausczik for their insightful suggestions on drafts of this article. Correspondence concerning this article should be addressed to David M. Buss, 1 University Station, Department of Psychology, University of  Texas, Austin, TX 78712. E-mail: [email protected] 1 Key terms defined in the Appendix are printed in boldface the first

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not be used as solutions to the adaptive problems of  mate   mate selection  (e.g., avoiding those who inflict costs) or  habitat  selection   (e.g., (e.g., choos choosing ing a site containing containing resour resources ces and refuge). Consequently, evolutionary psychologists suggest that the human mind is a complex integrated assembly of  many functio functionally nally speci specialized alized psych psychologic ological al adapt adaptations ations thatt evo tha evolve lved d as sol soluti utions ons to num numero erous us and qua qualita litativ tively ely distinct distin ct adapt adaptive ive proble problems—a ms—a premise about adaptations adaptations shared widely by evolutionary biologists in understanding nonhuman animals (Alcock, 2005). Psychological adapta-

 Jaime C. Confer

stati statistical stically ly reliab reliable le cues of fertil fertility ity in potent potential ial mates). Psychological adaptations information-processing circuits that take in delimited  are units of information and trans-

tio tions ns ofte often nasint intera eract cta wit with h eac each other oth er simultaneously to pro produc ducee ada adapti ptive ve behavior, when person ish faced with the adaptive problems of hunger and a threatening lion; fear of the lion will temporarily suspend hunger pangs until the threat of imminent death has passed (Buss, 2008). The list of ada adaptiv ptivee pro proble blems ms ext extend endss far bey beyond ond avoiding avoidi ng snake snakes, s, selec selecting ting nutritious food, and favoring fertile mates. It includes problems of parental investment (e.g., socializing sons and daughters), kinship (e.g., channeling nel ing alt altrui ruism sm tow toward ard clo close se rat rather her tha than n dis distan tantt gen geneti eticc relatives), friendship (e.g., detecting cheaters), coalitional cooperation (e.g., punishing free riders), selective aggression (e.g., diffusing a violent confrontation), negotiating status hierarchies (e.g., besting close rivals; dealing with subordinate status), and many others (Buss, 2008). Psychologi lo gica call ad adap apta tatio tions ns ar aree no nott se sepa para rate te “m “mod odul ules es”” in th thee

form that information into functional output designed to solve a particular adaptive problem. Evolved fear adaptations provide relatively uncontrovers ve rsia iall ex exam ampl ples es th that at ar aree we well ll su supp ppor orte ted d em empi piri rica call lly y ¨ hm ¨ hm (Min (M inek ekaa & O hman an,, 20 2002 02;; O hman an & Mi Mine neka ka,, 20 2003 03). ). Snakes and spiders, for example, signal potentially dangerous threats to survival. A programmatic series of studies has shown that an intense fear of snakes exists in humans and other primates; snakes and spiders embedded in complex visual arrays autom automatical atically ly captu capture re atten attention tion far more than tha n do har harmle mless ss obje objects cts—th —they ey “po “pop p out out”” of the visual visual array; humans rapidly condition to fear snakes more than most other stimuli; and the snake fear adaptation is selectively and automatically activated, it is difficult to extin-

Fodorian (Fodor, 1983)share sensecomponents of informational encapsulation; rather, they often component s and interact with each eac h oth other er to prod produce uce ada adapti ptive ve beh behavi avior or (se (seee Bar Barret rettt & Kurzban, 2006, for a cogent discussion of this issue). Evolutionary psychologists are not monolithic in their theoretical theore tical stances. There exist legitimate scientific differences on key issues such as the importance and meaning of  individual differences (Buss, 2009; Nettle, 2006; Tooby & Cosmid Cos mides, es, 199 1990), 0), the exi existe stence nce and fun functi ctions ons of mor moree domain-gene domain -general ral psycho psychologica logicall mecha mechanisms nisms such as fluid intelligence (Geary, 2009), and the importance of   group selection (Williams, 1966; D. S. Wilson & Wilson, 2007). Nonetheless, evolutionary psychologists all share the view that understanding the evolved functions of psychological adaptations—the problems they were “designed” by a prior histor his tory y of sel select ection ion to sol solve ve (no forw forward ard-loo -lookin king g inte intent nt

guish, and be 2002; tracedsee to Rakison specialized neural circuitry ¨ can (Mineka & itO hman, & Derringer, 2008, on the evo evoluti lution on of spe specia cializ lized ed spi spider der det detect ection ion ada adapta pta-tions). Evolutionarily ancient dangers such as snakes, spiders, heights, and strangers consistently appear on lists of  common fears and phobias far more often than do evolutionar tio narily ily mod modern ern dan danger gerss suc such h as car carss and gun guns, s, eve even n though cars and guns are more dangerous to survival in the modern environment. environment. The functi functional onal outputs of evolv evolved ed fear adaptations, such as freezing, fighting, and fleeing, are specifically designed to solve the adaptive problems posed by th thes esee ev evol olut utio iona nari rily ly re recu curre rrent nt th thre reat atss to su surv rviv ival al (Bracha, 2004). Adaptive problems are many in number. Solutions to one problem often fail to successfully solve other problems. Solutions to the adaptive problems of  food   food selection

implied)—is indispensable, not an ingredient for a mat mature ureanpsy psycho cholog logica icall sci scienc ence. e. optional, Unders Und erstan tandin ding g the evolved function of a psychological mechanism, or  why  it exists (often referred to as an  ultimate explanation) provides a complementary level of analysis to that of understanding the details of   how   the mechanism works (often referred to as a   proximate explanation). Both types of  explanation are required for a complete understanding, and indeed they mutually inform one another. Knowledge of  the human liver, for example, would be incomplete without understanding its evolved functions (e.g., to neutralize toxins) as well as the specific processes by which those functions are achieved (e.g., the lobules that produce bile and emulsify emuls ify lipids lipids). ). Simila Similarly, rly, knowle knowledge dge of psych psychologic ological al adaptations such as stranger anxiety in infants would be incomplete without understanding their functions (to avoid

(e.g., avoiding substances containing toxins) generally can-

potentially dangerous humans) as well as the specific pro-

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ered or documented (the phrase  design features is standard shorthand shorth and in evolut evolutionary ionary biology for attribu attributes tes or compo compo-nent parts of an adaptation that have been forged or “designed” by a past history of natural selection; no forwardlooking or intentional process is implied by this phrase; see, e.g., Hauser, 1999). A recent example comes from a research program on “adaptive “adap tive memory.” Nairne and his colle colleagues agues hypothesized siz ed tha thatt evo evolve lved d mem memory ory sys system temss sho should uld be at lea least st somewh som ewhat at dom domain ain spe specifi cific, c, sen sensit sitive ive to cer certai tain n kin kinds ds of 

 Judith A. Easton

cesses by which they operate—a predictable developmental emergence at 6 to 8 months, a special sensitivity to strange males more than strange females, emotional systems activated internally, external behavioral signaling to caregivers through crying, the activation of specific neural circuitry, and so on. Knowledge of ultimate functions is invaluable in guiding the search for the proximate causes, just as understanding stand ing proxim proximate ate implem implementat entation ion inform informss the searc search h for ultimate function. Evolut Evo lution ionary ary psy psycho cholog logy y use usess all of the sta standa ndard rd methods of investigation available to psychologists to test hypotheses hypoth eses,, includ including ing labora laboratory tory exper experiments iments,, observ observaational techniques, questionnaires, physiological techniques, mechanical recording devices, genetic methods, and brain imaging imagin g techni techniques. ques. In additi addition, on, evolu evolutionar tionary y psych psycholoologists sometimes use methods not typically used by psychologists, such as comparative analyses across species, ethnographicc record graphi records, s, arche archeologic ological al record records, s, paleon paleontologi tological cal data, and life-history data (Schmitt & Pilcher, 2004).

cont co nten entt Pandeirada, or in info forma rmatio tion n (N (Nai airn e & Pand Pa ndei eira rada da,,Nairne, 2008 20 08;; Nairne, Gregory, &rne Van Arsdall, 2009; Pandeirada, & Thompson, 2008). They hypothesized that human memory should be especially sensitive to content relevant to evolutionary fitness, such as survival (e.g., food, predat pre dators ors,, and she shelte lter) r) and rep reprod roduct uction ion (e. (e.g., g., mat mating ing). ). Using a standard memory paradigm involving a scenario primin pri ming g tas task k and a sur surpri prise se rec recall all task, they fou found nd tha thatt words previously rated for survival relevance in scenarios were subsequently remembered at significantly higher rates than th an wo words rds ra rate ted d fo forr re rele leva vanc ncee in a va varie riety ty of co cont ntro roll scenar sce nario io con condit dition ions. s. Fur Furthe thermo rmore, re, Nai Nairne rne and his col col-leagues conducted additional experiments that pitted survival processing against well-documented powerful encoding techniques, such as ease of generating a visual image, ease of generating an autobiographical memory, and intentional in awhich subjects were instructed ber thelearning words for later test. Interestingly, rating to therememitem’s relevance in the survival scenario produced better recall performance than did   any   of the other well-known memory-enhancing techniques. The researchers concluded that “survival processing is one of the best encoding procedures yet identified in human memory research” (Nairne & Pandeirada, 2008, p. 242). Had the results failed to confirm the predictions predic tions about specialized specialized sensi sensitivity tivity to surviv survival-rel al-releevant content, Nairne Nairne’s ’s adapti adaptive ve memory hypothesis hypothesis would have been falsified. A second example of a collection of hypotheses that have been tested and subjected to the risk of falsification derivess from   error management theory  (Haselton & Buss, derive 2000 20 00,, 20 2003 03,, in pr pres ess; s; Ha Hase selto lton n & Ne Nettl ttle, e, 20 2006 06). ). In an uncertain world in which observable cues are only proba-

The logic of hypothesis testing in evolutionary psychology is the same as hypothesis testing in all sciences (see Ketelaar & Ellis, 2000, for an extended discussion of falsifiability). abilit y). The resea researcher rcher first formula formulates tes a hypoth hypothesis esis about an evolved psychological mechanism and then generates testable predictions about the attributes or  design features

bilistically related to One the true ofisreality, there two possible ways to err. waystate to err to infer thatare a state exists when it does not, as when a rustle in the leaves does not signal a snake but rather was caused by a gust of wind. The other way to err is to infer that a state does not exist when it actually does, as in a failure to infer that a snake exists on the basis of a rustling of leaves when a snake truly doess exi doe exist. st. Acc Accord ording ing to erro errorr man manage agemen mentt the theory ory,, the costs of making these two types of errors (false positive vs. false negative) under conditions of uncertainty were often recurrently asymmetric in the currencies of survival and reproduction. The cost of failing to detect a snake in the leaves, in this example, could result in death; the cost of  erroneously inferring a snake that does not exist results in a trivial expenditure of energy in avoiding something harmless. If these and other asymmetric costs of errors recur

of that mechanism that have not previously been discov-

overr gen ove genera eratio tions, ns, sel select ection ion is hyp hypoth othesi esized zed to fav favor or the

Common Queries About Evolutionary Psychology  We now turn to some common queries about evolutionary psychology and endeavor to provide answers to them.

1. Can evolutionary psychological  hypotheses be empirically tested or falsified? 

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tion  is that women will prefer men as potential mates who

express a willingness to invest in them and their offspring (Buss, 1995). This is derived from the  hypothesis  that in patern pat ernall ally y inv invest esting ing spe specie cies, s, fem female aless wil willl use cue cuess to a man’s willingness to invest as a criterion for mate selection ti on.. In tu turn, rn, th this is hy hypo poth thes esis is is de deri rive ved d fro from m   parental investment inves tment theor theoryy, which posits that the sex that invests more in its offspring will be the choosier sex when selecting mates (Trivers, 1972). Finally, the logic behind parental investment theory is derived from  inclusive fitness theory

evolution of cognitive biases that are designed to err in the

(Hamilton, (Hamil ton,natural 1964a,selection. 1964b), the formulat formulation ion of evolution by As modern in all realms of psychological science, the evaluation of each evolutionary psychological hypothesis, as well as the broader theories within which they are embedded, rests with the cumulative weight of the empirical evidence. Althou Alt hough gh evo evoluti lutiona onary ry psy psycho cholog logy y is a rel relati ativel vely y young field, hundreds of empirical studies have been conducted to test a variety of evolutionary psychological hypothes pot heses. es. Some have bee been n con confirme firmed; d; oth others ers hav havee bee been n falsified; and others have not yet been subjected to enough empi em piri rica call te test stss to re rend nder er a fir firm m sc scie ienti ntific fic co conc nclu lusi sion on.. Among those that have been confirmed by multiple methods in multiple samples by multiple investigators are antifree-rider free-ri der adapt adaptations ations in coope cooperative rative groups (e.g., Price, Cosmides, & Tooby, 2002); cheater-detection adaptations

least Error costlymanagement direction. theory logic has been used to test hypotheses hypoth eses about adaptive biases in domain domainss rangin ranging g from visual and acoustic perception to inferences about sexual and homicidal motivation in other people. In the domain of  visual perception, for example, the  descent illusion hypothesis  (Jackson & Cormack, 2007) was used to predict that people would make asymmetric distance estimations when  judging from the top versus the bottom of a tall structure, owing to the dangers associated with falling from heights. Tests of the descent illusion hypothesis show that people perceive distances viewed from the top of tall structures to be 32% greater than precisely the same objective distances when viewed from the bottom, confirming the prediction (Jackson & Cormack, 2007). On the basis of error management theory logic, Neuhoff (2001) confirmed empiri-

in social exchange (e.g., Cosmides & Tooby, female superiority in spatial location memory as part 2005); of a gathering adaptation (e.g., Silverman & Choi, 2005); functional attributes of male and female short-term mating strategies (e.g., Greiling & Buss, 2000; Schmitt, 2005; Schmitt & Internationa Intern ationall Sexual Sexuality ity Desc Description ription Project, 2003); sexdifferentiate differe ntiated d decep deception tion tactics in human mating (e.g., Haselton, Buss, Oubaid, & Angleitner, 2005; Tooke & Camire, mir e, 199 1991); 1); ant antipr ipreda edator tor ada adapta ptatio tions ns in chi childr ldren en (e. (e.g., g., Barrett, 2005); and dozens more (see Buss, 2008, for a recent review). Among those that either have been falsified or have failed thus far in empirical tests are the kin altruism theory of male homosexuality (Bobrow & Bailey, 2001); the hypothesis that males have an evolved preference for virginity in selecting long-term mates (Buss, 1989); and at least one

audit auditory oryaching looming loomin g bias—  cal cally ly stimate thatt hum tha humans ansclose have an  of they they overestimat overe e the closeness ness approaching appro sounds compared par ed wit with h rec recedi eding ng sou sounds nds,, bec becaus ausee of the his histori torical cally ly greaterr dange greate dangers rs assoc associated iated with approa approaching ching rather than receding objects and predators. In the social realm, Haselton and Buss (2000) confirmed the existence of a  commitment skepticism bias  in women, such that they underinfer levels of romantic commitment (compared with men) that are based on cues such as declarations of love. The important point is that had any of the empirical tests failed, they would have falsified the descent illusion hypothesis, the auditory looming hypothesis, or the commitment skepticism hypothesis. The science of confirming and falsifying hypotheses, of course, is typically more complex than these examples indicate. Often a hypothesis is embedded within a larger

version of the “competitively disadvantaged male” hypothesis about rape (Lalumie (Lalu mie`re, `re, Chalm Chalmers, ers, Quinse Quinsey, y, & Seto, 1996). The kin altruism hypothesis of male homosexuality, for example, contends that homosexuality is an adaptation that involves a shift among those whose heterosexual heterosexual mating prospects are not promising from direct mating effort to investing in kin, such as the children of one’s brothers and sisters (E. O. Wilson, 1978). In a direct test of this hypothesis, Bobrow and Bailey (2001) used samples of heterosexual and homosexual men matched for age, education, and eth ethnic nicity ity.. The They y ass assaye ayed d gen genero erosit sity y tow toward ard fam family ily members; financial and emotional investment; avuncular tenden ten dencie cies, s, suc such h as wil willin lingne gness ss to giv givee gif gifts ts or cas cash h to support nieces or nephews; and general feelings of closeness toward genetic relatives. The results proved conclusive—they found no evidence for any of the key predic-

theoretical network. For example, one evolutionary  predic-

tion ti onss ma made de by th thee ki kin n al altr trui uism sm hy hypo poth thes esis is of ma male le

Diana S. Fleischman

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merous domain-specific adaptations. Although these claims may have int intuiti uitive ve app appeal eal,, we sug sugges gestt tha thatt the they y are of  dubiouss validi dubiou validity ty as cogen cogentt scien scientific tific expla explanation nations. s. The emotion of romantic jealousy provides a concrete example. Although dozens of studies had been conducted on romantic jealousy, it was not until evolutionary psychologists hypothesized sex differences in evolved design features that such differences were discovered (Buss, Larsen, & Westen, 1992; 199 2; Da Daly, ly, Wil Wilson son,, & We Wegho ghors rst, t, 198 1982; 2; Sym Symons ons,, 197 1979). 9). Because  paternity uncertainty has been a recurrent adaptive

homosexuality. Subsequent empirical tests have also failed

prob problem lem for men, evol evolutio utionary nary psycholo psyc hologist gistss hypo hypothes ized that men’s jealousy would be especially triggered bythesized cues to sexual infidelity, whereas women’s jealousy would center on emotional infidelity (i.e., cues that signal the long-term diversion of commitment and resources, such as a mate falling in love with another woman). Although both sexes experience jealousy over a partner’s sexual   and  emotional infidelity, abundant empirical evidence from studies employing more than half a dozen different experimental methods supports the existence of  sex differences in the relative weighting given to cues to infidel infi delity ity (for recent recent rev review iews, s, see Buss, 200 2008; 8; Bus Busss & Haselton, 2005; and Sagarin, 2005). Independent replication is the hallmark of the scientific method, however, and a meta-analysis of 72 studies found a strong effect size (d     0.64) in support of the hypothesized sex differences

to support the kin altruism hypothesis,and finding no significant differences between homosexuals heterosexuals in generosity toward kin, general feelings of familiality, or willin wil lingne gness ss to inv invest est in nie nieces ces or nep nephew hewss (Ra (Rahma hman n & Hull, 2005). On the basis of the current empirical evidence, we ca can n co conc nclu lude de tha thatt th thee ki kin n al altr trui uism sm th theo eory ry of ma male le homosexuali homos exuality ty has been refuted. The key point is that precisely formulated evolutionary psychological hypotheses that yield specific predictions about design features that are not known to exist prior to empirical testing are fully amenable to empirical confirmation and falsification. Evolutionary psychological hypotheses, like those from other theoretical perspectives within psychology, vary in their quality, their precision, and the degree deg ree to whi which ch the they y are anc anchor hored ed in wel well-es l-estab tablis lished hed theoretical foundations. Sloppy and imprecise evolutionary

(Hofhansl, Voracek, although an occasional study will fail&toVitouch, find full2004), support for them (e.g., Penke & Asendorpf, 2008). The fact that the sex differences have been documented using highly diverse empirical methods, ranging from sponta spontaneous neous memorial recall of  cues of sexual versus emotional infidelity (Schu¨ tzwohl & Koch, 2004) to sex-differentiated patterns of neural activation using fMRI technology (Takahashi et al., 2006) suggests that the burden of proof must now shift to those who doubt the existence of evolved sex differences in the emotion of jealousy (Buss & Haselton, 2005). After these previo previously usly unknown sex differences were discovered as a consequence of evolutionary psychological hypotheses, others have offered post hoc explanations for their the ir exi existe stence nce tha thatt inv invoke oke dom domain ain-ge -gener neral al rat ration ionali ality. ty. C. R. Harris and Christenfeld (1996), for example, sug-

hypotheses that fail to generate precise predictions deserve scientific scien tific criticism. The sometimes somet imes reflexive charge that evolutionary psychological hypotheses as a rule are mere “just“ju st-so so sto storie ries,” s,” how howeve ever, r, is sim simply ply erro erroneo neous, us, as the examples above demonstrate.

Some psychologists react to hypotheses about evolved psychological mechanisms by invoking concepts such as domain-genera main-g enerall rationa rationality lity as altern alternative ative explan explanations ations,, suggesting that “people just figure it out.” Some propose that it is more parsimonious to postulate one or a few domain-

gested that the differences are duehave to “rationality combined with the sex general desire people to keep what is theirs” (p. 378). They concluded by proposing that “the domain-general mechanism of rational thought” (p. 379) can explain the findings. Although we do not deny that humans are capable of rational thought, there are several problems with “the domain-general mechanism of rational thought” as an alternative explanation for most hypotheses thatt inv tha invoke oke spe specia cializ lized ed evo evolve lved d psy psycho cholog logica icall mec mechahanisms:: failur nisms failuree to predic predict, t, combin combinatoria atoriall explos explosion, ion, povert poverty y of the stimulus, and context-specificity. We address these problems in turn. The fai failur lure-t e-to-p o-pre redic dictt pro proble blem. m.   Domaingeneral rational thought, as it has been used as an explanation, is typically invoked post hoc to account for new empirical findings discovered as a consequence of novel

general mechanisms such as “rationality” rather than nu-

evolutionary evolut ionary psych psychologic ological al hypoth hypotheses eses.. Domain Domain-gene -general ral

Cari D. Goetz

2. Don’t people just solve problems using  rationality? Wouldn’t one domain-general  rationality mechanism be more  parsimonious than postulating many  domain-specific mechanisms? 

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quence of this rati quence rational onal deliberation deliberation?? The pred predicta ictabili bility ty and rapidity of men’s jealousy in response to cues of threats to paternity points to a specialized psychological circuit rather than a response caused by deliberative domain-general rational thou thought. ght. Dedi Dedicate cated d psyc psycholo hologica gicall adap adaptati tations, ons, beca because use they are activated in response to cues to their corresponding adapti ada ptive ve pro proble blems, ms, ope operat ratee mor moree effi efficie cientl ntly y and eff effec ectiv tively ely for many man y ada adapti ptive ve pro proble blems. ms. A dom domain ain-ge -gener neral al me mecha chanis nism m “mustt eval “mus evaluate uate all alte alternat rnatives ives it can defin define. e. Permu Permutati tations ons being what they are, alternatives increase exponentially as the

David M. G. Lewis

rational thought has not, to our knowledge, been used to predict ors discover Consequently, it app appear ears to lac lack k new both bot hempirical heuris heu ristic ticfindings. and pre predic dictiv tivee pow power. er. Hypotheses Hypoth eses about motiva motivational tional priorities priorities are requir required ed to explain empirically discovered phenomena, yet they are not contained conta ined within domain-general domain-general ration rationality ality theori theories. es. A mechanism of domain-general rationality, in the case of   jealousy, cannot explain why it should be “rational” for men to care about cues to paternity certainty or for women to care about emotional cues to resource diversion. Even assuming that men “rationally” figured out that other men having sex with their mates would lead to paternity uncertainty tai nty,, why should men car caree abo about ut   cuckoldry   to beg begin in with? In order to explain sex differences in motivational concerns, conce rns, the “ratio “rationality nality”” mechan mechanism ism must be couple coupled d with auxiliary hypotheses that specify the origins of the sex differences in motivational priorities. Because it requires

problem complexity increases” (Cosmides & Tooby, 1994, p. 94). Consequently, combinatorial explosion paralyzes a truly domain-general mechanism (Frankenhuis & Ploeger, 2007). The poverty of the stimulus problem.   The sexual sex ual infi infidel delity ity of a man man’s ’s mat matee has bee been n sta statis tistic ticall ally y associated with increased paternity uncertainty over deep evolutionary time. It is highly improbable, however, that men could learn this statistical regularity during development. To do so, men would have to observe a large sample of instances of sexual infidelity (which tend to be cloaked in secrecy) and then associate them with potentially detectable cues to lack of paternity that would be displayed nine months, or even several years, later (e.g., lack of phenotypic resemblance to the putative father). In contrast, selection can favor specialized adaptations that exploit sta-

Domain-general theories of rationality imply a deliberate calculation of ends and a sample space of means to achieve those ends. Performing the computations needed to sift through that sample space requires more time than is available for solving many adaptive problems, which must be solved in real time. Consider a man coming home from work early and discovering his wife in bed with another man. This circumstance typicall typi cally y lead leadss to imme immediat diatee jeal jealousy ousy,, rage rage,, viol violence ence,, and sometimes murder (Buss, 2000; Daly & Wilson, 1988). Are men pausing to ratio rationall nally y deli delibera berate te over whether whether this act  jeopardi  jeop ardizes zes thei theirr pate paternit rnity y in futu future re offs offsprin pring g and ulti ultimate mate

tistical tistical regularities regula ritiesxt-specific that are not detec detectable table ontogenetic ontogenetically. ally. The context-spe conte cific rationalit ratio nality y prob problem. lem. From an evolut evolutionary ionary perspective, perspective, there exist existss no domain domain-generall criteri genera criterion on of “ratio “rationality nality.” .” It is often reproductively reproductively rational for a mateless man on a path toward reproductive oblivion oblivi on to take life-shortening life-shortening risks to chang changee course course—to —to engage in steep future discounting (M. Wilson & Daly, 2004). In contrast, such risk taking would be reproductively irrational from the perspective of a man who has a wife and three thr ee you young ng chi childre ldren n to pro protec tect. t. Wha Whatt wou would ld hav havee bee been n rational from the perspective of an attractive high-status man in our ancestral past (e.g., securing multiple mates through polygyny, affairs, or short-term mating) would be evolutionarily irrational from the perspective of an attractive high-status woman, who would be better off securing a lo long ng-te -term rm ma mate te of hi high gh ge gene neti ticc qu qual alit ity y wh who o is bo both th willing and able to invest in her and her children (Buss & Shacke Sha ckelfor lford, d, 200 2008). 8). Bec Becaus ausee wha whatt is “ra “ratio tional nal”” diff differs ers across acr oss ada adapti ptive ve pro proble blems, ms, sex sexes, es, age ages, s, and life cir circum cum-stances, there exists no single domain-general criterion of  rationality. In sum, domain-general mechanisms such as “rationality” fail to provide plausible alternative explanations for psychological phenomena discovered by evolutionary psycholog cho logist ists. s. The They y are inv invoke oked d pos postt hoc hoc,, fai faill to gen genera erate te novel empirical predictions, predictions, fail to speci specify fy underl underlying ying motivational priorities, suffer from paralyzing combinatorial explosion, and imply the detection of statistical regularities that cannot be, or are unlikely to be, learned or deduced ontoge ont ogenet netica ically lly.. It is imp import ortant ant to not notee tha thatt the there re is no single criterion for rationality that is independent of adap-

reproductive fitness, and then becoming enraged as a conse-

tive domain domain..

the of additional post hoc explanatory clauses for postulation each new empiri empirical cal pheno phenomenon, menon, “rationality” “rationality” itself  acquires the “lack of parsimony” problem sometimes erroneously leveled against specific evolutionary hypotheses.

The problem of combinatorial explosion.

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Althou Alt hough gh the field of psy psycho cholog logy y lac lacks ks a com comple plete te understanding of the nature of these learning adaptations, enough evidence exists to draw a few reasonable conclusions. Consider three concrete examples: (a) People learn to av avoid oid ha havi ving ng se sex x wi with th th thei eirr cl clos osee ge gene neti ticc re rela lati tive vess (learned incest avoidance); (b) peopl peoplee learn to avoid eating foods that may contain toxins (learned food aversions); (c) people learn from their local peer group which actions lead to increases in status and prestige (learn learned ed pres prestige tige crite crite-ria). There are compelling theoretical arguments and em-

Carin Perilloux 

3. Aren’t human behaviors the result of  learning and socialization, not evolution? 

pirica pirical l evidence that each of these forms ofthat learning is least best explained by evolved learning adaptations have at some specialized design features, rather than by a single all-purpose general learning adaptation (Johnston, 1996). Stated differently, differently, evolve evolved d learni learning ng adapt adaptations ations must have at least some content-specialized attributes, even if they share some components. Solving the adaptive problem of incest avoidance requires learning to avoid sexual contact with close genetic relatives who are, from a reproductive standpoint, inappropriate sexual partners due to  inbreeding depression. Empirica pir ically lly,, the there re is goo good d evi eviden dence ce for an evo evolve lved d inc incest est avoidance learning mechanism that is highly sensitive to reliable cues of close genetic relatedness, such as coresidence den ce dur during ing dev develo elopme pment nt (Li (Liebe eberma rman, n, Too Tooby, by, & Cos Cos-mides, 2003, 2007). Coresidence in the ancestral environ-

The framework of evolutionary psychology dissolves dichotomies such as “nature versus nurture,” “innate versus learned,” and “biological versus cultural.” Instead it offers a truly interactionist framework: Environmental selection pressures shape evolved mechanisms at the phylogenetic level (Fraley, Brumbaugh, & Marks, 2005). Environmental input influences their development at the ontogenetic level (e.g., Belsky, 2007; Bjorklund & Pelligrini, 2000; Ellis & Bjorklund, Bjorkl und, 2005). And the environment environment provid provides es cues that activate psychological adaptations at the immediate proximal level (e.g., Buss, 1995; Cosmides & Tooby, 2000). Thus, it does not make sense to ask whether calluses or mating mat ing dec decisi isions ons are “ev “evolv olved” ed” or “le “learn arned” ed” or due to “nature “na ture”” or “nu “nurtu rture. re.”” All evo evolve lved d mec mechan hanism ismss req require uire

ment wasnot a reliable cue of genetic although this does always hold true in the relatedness, modern environment, as in exp experi erimen ments ts wit with h Isr Israel aelii kib kibbutz butzim. im. Dur Durati ation on of  coresi cor esiden dence ce wit with h a mem member ber of the opp opposi osite te sex during childhood powerfully predicts lack of sexual attraction as well as the degree of emotional repulsion at the idea of  having sex with him or her (Lieberman et al., 2003, 2007; see Tyber, Lieberman, & Griskevicius, 2009, for empirical evidence for three evolved functions of emotional repulsion—sexual disgust, pathogen disgust, and moral disgust). Food aversions, on the other hand, require a different set of learning mechanisms and therefore result in a different set of learned behaviors. Humans, and most omnivores, learn food aversions through a mechanism that efficiently associates assoc iates the nausea with the ingestion of toxins or pathogens in food recently consumed, thereby producing disgust

som some e env environ ironmen mental tal skin input inp utin for their the ir ofact activa ivation tion,,orbe it repeated friction to the the case calluses observable cues to mate value in the case of mating decisions. The term  learning  is sometimes used as an explanation for an observed effect and is the simple claim that something in the organism changes as a consequence of  enviro env ironme nmenta ntall inp input. ut. Inv Invoki oking ng “le “learn arning ing”” in thi thiss sen sense, se, withoutt furthe withou furtherr speci specificatio fication, n, provide providess no additi additional onal explanat pla natory ory val value ue for the obs observ erved ed phe phenom nomeno enon n but onl only y regresses regres ses its cause back a level level.. Learn Learning ing requires evolved psychological adaptations, housed in the brain, that  enable learning to occur: “After all, 3-pound cauliflowers do not learn, but 3-pound brains do” (Tooby & Cosmides, 2005, p. 31). The key explanatory challenge is to identify the nature of the underlying learning adaptations that enable humans to change their behavior in functional ways as a conse-

and avoidance future encounters with the associat soc iated ed foo food d reactions (Domja (Do mjan, n, to200 2004). 4). Foo Food d ave aversi rsion on lea learni rning ng helps organisms to avoid ingesting substances that previously caused nauseous reactions to substances containing toxins or infectious microorganisms. Another set of learning mechanisms is responsible for incorporating information about status and prestige in the psychology of hierarchy negotiation (Henrich & Gil-White, 2001). 200 1). Amo Among ng hun hunter ter-ga -gathe therer rer soc societ ieties ies,, goo good d hun hunting ting skills lead to prestige (Hill & Hurtado, 1996). In academia, individuals indivi duals attain high prestige by publis publishing hing prominent papers that are cited by other scholars scholars (Penne (Pennebaker, baker, 2009). People learn prestige criteria, in part, by scrutinizing the attent att ention ion str struct ucture ure:: Tho Those se hig high h in pre presti stige ge are typ typica ically lly those to whom the most people pay the most attention (Chance, 1967). By attending to and imitating the qualities,

quence of particular forms of environmental input.

clothing styles, and behaviors of those to whom others pay

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Socialization  is another explanation that is sometimes

proposed as an alternative to evolutionary psychological explanations. Indeed, for much of 20th-century psychology, socialization was thought to be a powerful influence on human development, personality, and sex differences. This view was based on an old but extremely influential idea that “indiv “individual idual natures are merel merely y indete indeterminat rminatee materi te rial al th that at th thee so soci cial al fa fact ctor or mo mold ldss an and d tr tran ansf sfor orms ms”” (Durkheim, (Durkh eim, 1895/1 1895/1962, 962, p. 106). Although psych psychologis ologists ts are increasingly recognizing that evolved tendencies play

the most attention, humans learn the prestige criteria of 

some roleofinsocialization psychological development, historically theories implicitly assumed that the many mind was more or less a blank slate upon which parents, teachers, and other agents of socia socializati lization on wrote script scriptss (Pinke (Pinker, r, 2002 20 02). ). Em Empi piric rical al wo work rk ov over er th thee pa past st fe few w de deca cade dess ha hass gradually gradua lly changed this assu assumption mption.. Plomin and Danie Daniels ls (1987),, using behavioral genetic method (1987) methodologie ologies, s, showe showed d thatt sha tha shared red env enviro ironme nmenta ntall infl influen uences ces wit within hin the fam family ily (those typically assumed by traditional socialization theories) account for a trivial percentage of variance in personality ali ty and oth other er psy psycho cholog logica icall var variab iables les.. Furt Further hermor more, e, a meta-analysis of 172 studies of differential parental socialization practices of boys and girls discovered that “most effects were found to be non-significant and small” (Lytton & Romney, 1991, p. 267). The sole exception to this conclusion, from among the

their local culture Gil-White, 2001). (one form of social learning) (Henrich & These three forms of learning—incest avoidance, food aversion, and prestige criteria—require at least some content-specific specializations to function properly. Each operates on the basis of inputs from different sets of cues: coresidence during development, nausea paired with food ingestion, and group attention structure. Each has different functional output: avoidance of relatives as sexual partners, disgust at the sight and smell of specific foods, and emulation of those high in prestige. It is important to note that each form of learning solves a different adaptive problem. There are four critical conclusions to draw from this admittedly admitt edly brief and incom incomplete plete analysis. First, label labeling ing something as “learned” does not, by itself, provide a satisfact isf actory ory sci scient entific ific exp explan lanati ation on any mor moree tha than n lab labeli eling ng

19 key domains examined in the meta-analysis, centered sex-typed activities. Parents apparently encourage girls on to play with dolls and houses and boys to play with balls, bats, and toy trucks. Even within this delimited domain, however, the assumption of a unidimensional parent-to-child direction of effects has been undermined by other studies. Male vervet monkeys, like boys, prefer playing with “masculine” toys such as trucks; female vervet monkeys, like mostt girl mos girls, s, pre prefer fer “fe “femin minine ine”” toy toyss suc such h as Bar Barbie bie dol dolls ls (Hines, 2004). Levels of prenatal exposure to androgens influence within-sex differences, with females exposed to higher levels of androgens displaying more masculine appearance and behavior (Hines & Green, 1991). The relative dearth of evidence for the potency of parental socialization on subsequent psychological development has caused some theorists theori sts to shift their emphasis away from parental social-

something as “evolved” it is simply claim that environmental input is onedoes; component of the the causal process by whi which ch cha change nge occurs occurs in the organism organism in som somee way way.. Second, “learned” and “evolved” are not competing explanations; nation s; rather rather,, learni learning ng requir requires es evolve evolved d psych psychologic ological al mechan mec hanism isms, s, wit withou houtt whi which ch lea learnin rning g cou could ld not occ occur. ur. Third, evolved learning mechanisms are likely to be more numerous than traditional conceptions have held in psychology, cholog y, which typically have been limited to a few highly general learning mechanisms such as classical and operant conditioning. Operant and classical conditioning are important, of course, but they contain many specialized adaptive design features rather than being domain general (O¨ hman & Mineka, 2003). And fourth, evolved learning mechanisms are at least somewhat specific in nature, containing particular design features that correspond to evolved solu-

izatio ization n pract practices iceson shared children ren within families s and instead to focus peersby (J. child R. Harris, 2007)familie and withinfamily birth order (Sulloway, in press) to explain the nonshared share d enviro environmenta nmentall influen influences ces that behavi behavioral oral geneti geneticc methods have shown must exist. Given the large amount of effort that parents in all cultures expend on socializing their children, it would defy evolutionary logic if there were no adaptations in parents associated with socialization practices. Consequently, evolutionary lution ary psych psychologis ologists ts fully accept the potential importance of environmental influences, whether coming from parents, siblings within families, or peers, but they suggest that socialization theories will become more powerful if  informed informe d by evolut evolutionary ionary psychological psychological analys analyses es (Buss (Buss,, 2008; Ellis, Jackson, & Boyce, 2006). The  daughter guarding hypothesis —the idea that par-

tions to qualitatively distinct adaptive problems.

ents have evolved adaptations designed to socialize their

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David M. Buss

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daughters ters and sons differently differently in the sexual realm— exemdaugh plifies one approach to evolution-based theorizing about socialization (Perilloux, Fleischman, & Buss, 2008). According to the daughter guarding hypothesis, greater parental con constr strain aintt on the sex sexual uality ity of dau daught ghters ers wou would ld hav havee provid pro vided ed thr three ee func functio tional nal ben benefit efits: s: (a) pro protec tecting ting the their ir daughter’s sexual reputation, (b) preserving their daughter’s mate value, and (c) preventing their daughter from being sexually exploited (Perilloux et al., 2008). Using two separate data sources, young adults and their parents, Per-

place greater value on a potential mate’s physical attractiveness (Gangestad & Buss, 1993; Gangestad, Haselton, & Buss, 2006). In fact, ecological variation in parasite prevalence accounts for 52% of the cultural variation in the importance placed on physical appearance in a mate. The key poi point nt is tha thatt evo evoluti lutiona onary ry hyp hypoth othese esess abo about ut evo evoked ked culture can explain some forms of cultural variation, although obviously the extent to which it can do so remains to be determined. Transmitted (or adopted) culture describes a second

illoux to and her colleagues found that weremating more likely control their daughter’s thanparents their son’s decisions (e.g., by imposing an earlier curfew); reported more emotional upset over their daughter’s than their son’s sexual activity; and exerted more control over their daughter’s than their son’s mate choice decisions. In a massive crosscro ss-cul cultur tural al stu study, dy, Low (19 (1989) 89) fou found nd sup suppor portt for the evolution-based daughter guarding hypothesis in a study of  93 cultures—girls across cultures are taught to be more sexually sexua lly restra restrained ined than boys. These studies illustrate just one evolutionary approach to socialization practices (see Geary & Flinn, 2001, for an evolutionary analysis of parenting, and Ellis et al., 2006, for an evolutionary theory of adaptive phenotypic plasticity). Much theoretical and empirical work remains to be done, but we can already see that evolutionary and social-

formles of of cultural cultur al phenomena pheno (e.g., Norenzayan, Noren amp amples transm tra nsmitte itted dmena culture cul ture includ inc ludee zayan, belief bel iefss 2006). about abo ut Exthe afterlife, local moral repugnance at the thought of ingesting certain foods such as beef or pork, the content of certain stereo ste reotyp types es abo about ut out outgro group up mem member bers, s, and info informa rmatio tion n transmitted through gossip. In a series of studies testing hypotheses about adaptations for information transmission, McAndrew, Bell, and Garcia (2007) found predictable patterns of content and persons to whom gossip is spread. Indivi Ind ividua duals ls spr spread ead dam damagi aging ng gos gossip sip rap rapidl idly y and wid widely ely about rivals but tend to conceal it about friends or lovers. Sexual rivals tend to targe targett potent potential ial mates as recipi recipients ents of  derogatory rumors about their competitors. And men and women differ in the content of gossip they spread about their the ir riv rivals als,, wit with h men focusing focusing mor moree on defi deficie cienci ncies es in athlet ath letic ic and pro profes fessio sional nal pro prowes wesss and wom women en foc focusi using ng

ization mutually to exclusive; in someexplanations cases, they are cannot be necessarily usefully integrated provide novel predictions.

nations that invoke evolved psychology, most frequently when cross-cultural variability is observed. Cultural explanations sometimes invoke the notion that differences between groups are prima facie evidence that “culture” is an autono aut onomou mouss cau causal sal age agent nt tha thatt cre create atess the con conten tentt of the human mind (see Buss, 2001, for an extended discussion of  the myth of culture as a causal explanation). Although the ambiguous referent “culture” is generally presumed to have a single, coherent meaning, it can actually refer to at least

more appearance andNo sexual Dedden, 1990;on Campbell, 2004). one conduct claims to(Buss have & articulated a comprehensive explanation of any particular instance of  transmitted culture. Nonetheless, satisfying explanations of  transmitted culture will involve at least the following elements: men ts: (a) psy psycho cholog logica icall ada adapta ptation tionss in ind indivi ividua duals ls designed to selectively transmit ideas, beliefs, or representations to others; (b) psychological adaptations in receivers designed to selectively accept some ideas from among the available welter of ideas (Flinn, 1997); and (c) psychological adaptations designed to discount or reject other ideas from the available cultural pool on the basis of qualities such as source credibility and conflicts of fitness interests (Cos (C osmid mides es & To Toob oby, y, 20 2000 00). ). As Al Allp lport ort an and d Po Post stma man n (1947, p. 314) astutely observed long ago, “Rumor is set into motion and continues to travel based on its appeal to

culture cult urecircum two distin dis tinct ct con concep ts: (a) —differential output elicited bycepts: variable variab le   evoked between-gro betwe en-group up circumstanc stances es operating as input to a universal human cognitive architecture; and (b)   transmitted transmitted culture—th —thee sub subset set of ide ideas, as, values, and representations that initially exist in at least one mind min d tha thatt com comee int into o exi existe stence nce in oth other er min minds ds thr throug ough h observation or interaction (Tooby & Cosmides, 1992). Neither of these distinct senses of culture, however, can be divorced divorc ed from the conte content-str nt-structurin ucturing, g, evolve evolved d organi organizazation of the human mind. Evoked culture arises from human cognitive architecture and expresses itself differentially according to local conditions. Mate preferences for physical appearance, for example, have been hypothesized to vary across cultures according to local levels of pathogen prevalence. Parasites are known to degrade physical appearance. In geographic

the personal interests of the individuals involved in the strong transmission.” Transmitted culture, if it is passed down over many generations, can in turn create new selection pressures for novel human adaptations (Cochran & Harpending, 2009). An adaptation for the digestion of dairy products, a product of the cultural invention of agriculture, provides one welldocumented physiological example. A possible psychological example is the modern rise of sociopathic traits as a conseq con sequen uence ce of liv living ing in lar large ge cit cities ies,, whi which ch low lowers ers the reputa rep utatio tional nal cos costs ts of pur pursui suing ng a str strate ategy gy of dec decept eption ion,, cheating, and defection (Buss & Duntley, 2008; Mealey, 1995). Just as transmitted culture rests on a foundation of  evolved psychological adaptations, novel adaptations can evolve as a consequence of transmitted culture. Whether humans have evolved psychological adaptations over the

regions with higher parasite loads, both men and women

past 10,000 years for other culturally transmitted inven-

4. How does evolutionary psychology take  culture into account?  Culture  is sometimes advanced as competing with expla-

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tions, such as cash economies, remains an open question. Although ground has barely been broken on adaptation– culture coevolutionary processes (sometimes called gene– culture coevolution), theoretical work suggests that this is a promis pro mising ing ave avenue nue of res resear earch ch (Co (Cochr chran an & Har Harpen pending ding,, 2009; Richardson & Boyd, 2005). The stance of evolutionary psychology toward culture can be sum summar marize ized d by sev severa erall key poi points nts:: (a) Cul Cultura turall phenomena are real and require explanation; (b) labeling something as “culture” is simply a description, not a causal

(Buss, 2000). In the modern world, however, if a man’s wife is taking birth control, male sexual jealousy adaptations could be considered superfluous in the prevention of  investing inves ting in unrela unrelated ted offspr offspring. ing. If the relevant adaptation were a general motivation to maximize maximi ze reprod reproductive uctive success (which cannot evolv evolvee in principle—see Tooby & Cosmides, 1990), then the wife’s contraception should short-circuit or dispel her partner’s sexual jealousy. If the relevant adaptation is a powerful emotion triggered by modern instances of ancestral cues,

explanation; (c) it phenomena, is useful to distinguish between different forms of cultural such as evoked culture and transmitted trans mitted culture; (d) explai explaining ning evoked cultur cultural al phenomena requires an understanding of the evolved psychological mechanisms and the relevant environmental input involved in their elicitation; (e) explaining transmitted culturee req tur requir uires es the inv invoca ocatio tion n of evo evolve lved d psy psycho chologi logical cal mechan mec hanism ismss in bot both h tra transm nsmitte itters rs and rec receiv eivers ers;; and (f) transmitted culture, if recurrent over generations, can influence the evolution of novel adaptations, which in turn can affect transmitted culture, theoretically producing adaptation– culture coevolutionary processes.

such as witnessing one’s mate kissing a rival, then knowledgee of the wif edg wife’s e’s con contra tracep ceptio tion n wou would ld not pre preven ventt the activation of her partner’s sexual jealousy. Psychological adaptations will be activated by the cues, or close approximatio ima tions ns of tho those se cue cues, s, tha thatt tho those se ada adapta ptatio tions ns wer weree designed sig ned to det detect ect,, reg regard ardles lesss of whe whethe therr the ada adapta ptatio tions ns curren cur rently tly ser serve ve the fun functi ctions ons for whi which ch the they y ori origina ginally lly evolved. In order for contraception to affect male sexual jealousy, the selection pressures introduced by its invention would have to fashion new, or modify existing, psychological mechanisms. mechanisms. For such comple complex x adapt adaptations ations to evolve evolve,, the selection pressures responsible for their design must be reliab rel iably ly and rec recurre urrentl ntly y fac faced ed for mul multip tiple le gen genera eratio tions. ns. Effective contraception is a very recent invention on the

5. How do recent novel environmental  phenomena affect human evolutionary  psychology? 

question. First, mismatches modern and ancestral env environ ironmen ments ts may negate neg ate between the ada adapti ptive ve uti utility lity of som somee evolved psychological mechanisms. Mechanisms that once influenced reproductive success may no longer have the same effect. Our evolved taste for foods containing fat and sugar, adaptive in the past, now leads to obesity and Type 2 diabe diabetes tes in modern environment environment replete with highly processed ces sed foo foods ds ava availa ilable ble che cheapl aply y and in gre great at abu abunda ndance nce.. Second, novel environmental stimuli, such as media images or pornography, may trigger, hijack, or exploit our evolved psychological mechanisms. Male sexual jealousy provides a specific example of a mismatch misma tch betwe between en ances ancestral tral and modern environments. environments. Male sexual jealousy almost certainly evolved, in part, to serve a patern paternity ity certainty function—motiva function—motivating ting men to ward off mate poachers, deterring a mate from sexually

timescale of human there has not been enough time forhistory. natural Consequently, selection to forge or modify complex psychological adaptations to effectively utilize the evolutionarily novel inputs associated with birth control. In somee way som ways, s, the there re exi exist st mis mismat matche chess bet betwee ween n the soc social ial world in which humans evolved and the modern worlds they now inhabit. The other way in which novel environmental influences can affect evolved psychology is when they hijack  our evolved psychological mechanisms by closely mimicking ancestral cues that the psychological adaptation was designed to detect. Pornography, for example, can activate a man’s sexual arousal adaptations, despite his inability to copula cop ulate te and impr impregn egnate ate a two two-dim -dimens ension ional al ima image ge of a woman on a page or computer screen (Symons, 1979). This activated adaptation was designed to elicit arousal at the sight of an attractive, unclothed, sexually receptive woman. In ancestral environments, such a sight would only have occurred occurr ed in a woman’ woman’ss actua actuall prese presence, nce, reliably indicating indicating a sexual opportunity. Consequently, there would have been no selection pressure to design a mechanism capable of  distinguishing between a situation in which a nude woman was seen and a sexual opportunity existed, and a similar situation situa tion lacking such sexua sexuall opport opportunity unity (e.g., a photograph of a nude woman). In short, modern cues that mimic ancestral cues can artificially hijack evolved psychological adaptations in ways that may not be currently adaptive. In some ways, of course, modern environments do resemble ancestral environments, and adaptations functional in the past may continue to be functional in the present, so the continuity of functionality must be determined on a case-

strayi str aying, ng, and avo avoidin iding g inv invest esting ing in a riv rival’ al’ss offs offsprin pring g

by-case basis.

Extremely novel recent environments, of course, have not had enough time to influence the evolution of psychological adaptations. adaptations. Humans live in modern environments environments that differ in some important ways from the ancestral environments to which our hominid ancestors adapted. Rather than collec col lectin ting g food via hun huntin ting g or gat gather hering ing,, peo people ple eat at restaurants resta urants and buy prepac prepackaged kaged food at the grocery store. Modern Mod ern com comput puters ers hav havee par partia tially lly rep replac laced ed fac face-to e-to-fa -face ce communicati commun ication, on, where whereas as increa increased sed geogra geographic phic mobili mobility ty has brought togeth together er previo previously usly isolated peoples. Through contraceptive technology, modern humans can sever the link between sexual intercourse intercourse and reprod reproduction uction.. How do these recent environmental novelties affect human evolved psychology? There are at least two approaches to answering this

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6. What role do genes play in the  framework of evolutionary psychology?  This is a complicated question that can be analyzed at a minimum of three levels—genetic determinism versus interactionism, genes underlying adaptations, and inferences about adaptations in the absence of knowledge of molecular-genetic substrate.

Genetic dete Genetic determin rminism ism vers versus us inte interacti raction-  on-  ism.   Genet Genetic ic determinism determinism is the view that genes determine phenotypes, phenotypes, such as morpho morphology, logy, psychology, psychology, or behavi ha vior or,, wi with th li litt ttle le or no en envi viro ronm nmen enta tall in influ fluen ence ce.. Evolutionary psychology forcefully rejects a genetic determinism stance and instead is organized around a crisply formulated interactionist framework that invokes the role of the environment at every step of the causal process. Environment Enviro nmental al input includes (a) the selec selection tion pressures that give rise to psychological adaptations; (b) the environments needed for the proper development of these mechanisms in individual humans; and (c) immediate proximate inputs necessary for their activation. Indeed, adaptations exist in their current form precisely because they historically solved adaptive problems posed by various environmental contingencies. To illustrate the inaccuracy of the notion that evolutionary psychology holds to a genetic determinist stance,

expression of that trait. Most characteristics are polygenic, that is, they are regulated by complex interactions of many genes in conjunction with specific forms of environmental input. Single genes rarely code for any complex mechanism, be it physiological or psychological. Although the discovery of the sickle cell gene led some scientists to be optimistic about finding other single-gene adaptations, decades of subsequent research have revealed few others. All adaptations, by definition, must have a genetic basis. If they did not, they could not have evolved by the process of  natural selection. This applies muchfear to brain-based chological adaptations such asassnake and cheaterpsydetection as it does to body-based physiological adaptations such as the kidneys and lungs.

Can you provide evidence for a psycho-  logica log icall ada adapta ptatio tion n wit witho hout ut doc docume umenti nting ng its  genetic basis?    Evolu Evolutionar tionary y psychologists psychologists often formulate hypotheses about adaptations, although some test hypotheses about by-products of adaptations (e.g., Kurzban,, Too ban Tooby, by, & Cos Cosmid mides, es, 2001) or noi noise se gen genera erated ted by mutations (e.g., Keller & Miller, 2006). Adaptations are typica typ ically lly defi defined ned by the com comple plexit xity, y, eco econom nomy, y, and effi effi-ciency of their design and their precision in effecting specific functional outcomes, not by the ability of scientists to identify identi fy their complex genetic bases (Willi (Williams, ams, 1966). For example, the human eye is indisputably an adaptation de-

consider one example of an environmental variable activating a plausible evolved psychological mechanism—the decrea dec rease se in tes testos toster terone one tha thatt occ occurs urs whe when n men ent enter er a long-term relationship such as marriage (Burnham et al., 2003) and the further decrease in testosterone after the birth of their first offspring (Gray, Yang, & Pope, 2006). This candidate adaptation is hypothesized to function to redirect thee ef th effo fort rt th that at a ma man n al allo loca cate tess aw away ay fr from om ma mati ting ng an and d toward tow ard the ada adapti ptive ve pro proble blem m of par parent enting ing.. The evo evolve lved d mechan mec hanism ismss inv involv olved ed in the reg regula ulatio tion n of and androg rogens ens in males obviously have a genetic basis, but in this context they are designed to use specific social cues in adjusting their levels (Gray, Parkin, & Samms-Vaughan, 2007). The key point of this example, whether or not further research confirms its nature and hypothesized function, is that evolutionary psychology furnishes an interactionist perspec-

signed for vision, basedproblems on the design features for motion, solving the particular adaptive such as detecting detec ting edges, colors, and contrasts. The reliably developing, universal, and complex design features of the eyes provide abundant abunda nt evide evidence nce that they are adapta adaptations tions for spec specific ific functions, even though scientists currently lack knowledge of the specific genes and gene interactions involved in the visual system. The same logic applies to psychological adaptations. Just as empirical research has documented snake fears, the auditory looming bias, and the descent illusion as adaptations tio ns wit withou houtt ide identi ntifyin fying g the their ir gen geneti eticc bas basis, is, so too can research resea rch confirm the exist existence ence of adapt adaptations ations for kin altruism, differential parental investment, and cheater detection in social exchange without identifying their genetic basis. The demonstration demonstration of speci specialize alized d functi functional onal design pro-

tive. adaptations are designed to respond socialPsychological conditions such as being mated or unmated, beingto a parent or being childless, being high or low in the status hierar hie rarchy chy,, and more gen genera erally, lly, con confro fronti nting ng one sui suite te of  adaptive problems rather than another. Although evolutionary psychology clearly rejects a blank slate view of the human mind, it just as clearly rejects genetic determinism and instead provide providess a detail detailed ed intera interactioni ctionist st framew framework  ork  (Pinker, 2002).

questions such as “Is there a jealousy gene?” or “Is there a gene for male aggression?” Genes do not code directly for partic par ticula ularr phy physio siolog logica icall or beh behavi aviora orall cha charac racter terist istics ics;; rather, they code for specific proteins. When geneticists say there is a gene for a particular trait, this is a shorthand way

vides some Identifying of the mostthe compelling forms evidence for adaptation. genetic basis of of a trait is neither necessary nor sufficient for demonstrating that the trait is an adaptation. Nonetheless, we expect that developments in molecular genetics will be increasingly useful in both testing and informing evolutionary psychological hypotheses. Individual variations in the alleles of the DRD4 gene provide one example. The 7R allele has been linked with novelty seeking and extraversion (Ebstein, 2006), and it occurs at dramatically different rates in different geographical regions (e.g., higher in North America than in Asia). This 7R allele of the DRD4 gene has been hypothesized to be advantageous in exploiting resources in novel environments (Chen, Burton, Greenberger, & Dmitrieva, 1999; Penke, Denissen, & Miller, 2007). The finding that the 7R allele is substan-

of indicating that the gene is involved in some way in the

tially more common in nomadic than in sedentary popula-

Is there a gene for each behavioral adap-  tation?    Evolu Evolutionar tionary y psych psychologis ologists ts sometimes receive

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tions supports this evolutionary psychological hypothesis (Eisenberg, Campbell, Gray, & Sorenson, 2008). In short, although althou gh molecular genetic analysis is not necessary necessary for carrying out the research program of evolutionary psychology, we anticipate that it will become increasingly useful to test and to inform some evolutionary psychological hypotheses.

7. What is the practical value of evolutionary  psychology? 

Anothe Ano therr pra practi ctical cal app applic licati ation on is in the are areaa of law law.. Legall sc Lega scho hola lars rs ar aree in incr crea easi sing ngly ly us usin ing g kn know owle ledg dgee of  evolved evolve d psych psychologic ological al adapt adaptations ations to unders understand tand how to better regulate human behavior and guide policy decisions. Evolutionary psychology helped to inspire the formation of  the Society for Evolutionary Analysis in Law (SEAL: see www.sealsite.org), which now has over 400 members spanning more than 30 countries. The practical legal applications include uncovering conflicts among simultaneously pursued legal policies; sharpening the cost–benefit analy-

Evolutionary psychology is a basic science, and as such it seeks a fundamental understanding of human nature—our evolved mechanisms of mind. Its conceptual framework  was developed as a metatheory for aiding psychological science, not specifically as an aid for practical applications. Nonetheless, insights provided by evolutionary psychology have increasingly been applied to practical societal problems. One practica practicall app applic licati ation on is in the field of cli clinic nical al psychology. The evolutionary clinical psychologist Steve Ilardi Ila rdi has dev develo eloped ped eff effect ective ive tre treatm atment ent for dep depres ressio sion n based on what he has hypothesized to be plausible mismatches between ancestral and modern environments. In ancestral times, people spent much of their day outdoors in sunshine, engaging in high-activity tasks such as hunting, gathering, building shelters, making tools, and tending to children. They lived in small tightly knit groups rather than isolat iso lated ed nuc nuclea learr fam familie ilies. s. And the their ir die diets ts diff differe ered d from most modern diets. His six-step treatment for depression includes increasing omega-3 fatty acid consumption, getting tin g at lea least st 30 minu minutes tes of dai daily ly exp exposu osure re to sun sunlig light, ht, rampin ram ping g up exe exercis rcise, e, soc social ializi izing ng dai daily ly wit with h frie friends nds and family, engaging in antiruminative activity, and adopting patterns of good sleep hygiene—all procedures designed to mimic ances ancestral tral living conditions. conditions. This evolution-based evolution-based therapy has produced a 14-week success rate of 75.3%, defined defi ned as a gre greate aterr tha than n 50% reduction reduction in dep depres ressiv sivee symptoms, compared with a 22% success rate for a waitlist control group (Ilardi et al., 2007). These results do not imply that depression was absent in anc ancest estral ral tim times. es. Indeed, Indeed, the there re is evi eviden dence ce tha thatt som somee

ses thattanding oftenginfluence legal policymaking; policymaki ng; increasing our understandin unders about human decision decis ion makin making; g; disen disentantangling the multiple causes of various law-relevant behaviors; exposing a variety of unwarranted assumptions underlying legal approaches for inspiring behavioral changes; assessing the comparative effectiveness of legal strategies used to changee speci chang specific fic behav behaviors; iors; and ident identifying ifying undernoticed undernoticed and unintended selection pressures that legal systems can themselves create (Jones & Goldsmith, 2005). Evolutionary analysis sheds light on the complex factors behind sexual harassment, sexual assault, and infanticide, cid e, hel helpin ping g gui guide de leg legal al ini initia tiative tivess to aid in det deterri erring ng future fut ure ass assaul aults ts (Jo (Jones nes,, 199 1997, 7, 199 1999; 9; Jon Jones es & Gol Goldsm dsmith ith,, 2005). To take one concrete example, sexual harassment and stalking laws typically invoke what is called a “reasonable person standard,” which means that a person can

for forms ms offunctions, depres dep ressio sion n (oraslow mood) may differthat different ent adaptive such disengaging fromserve strategies are not working, aiding people to be more objective in reassessing their goals, signaling to loved ones that they are in need of help, or conserving energy (e.g., Andrews & Thomps Tho mpson, on, 2009; Kel Keller ler & Nes Nesse, se, 2006; Nes Nesse se & Wil Wil-liams, 1994; Stevens & Price, 1996; Watson & Andrews, 2002). 200 2). Non Noneth ethele eless, ss, rat rates es of dep depres ressio sion n app appear ear to hav havee increased dramatically in the modern environment (Kessler ¨ stu¨ n, 2008). A deeper evolutionary understanding of  & U the common modern problem of depression, including its possible functions as well as the ways in which mismatches between ancestral and modern environments exacerbate it, can lead to better preven prevention tion and treatm treatment. ent. Although clinical applications are just beginning, evolutionary psychology is sta starti rting ng to yie yield ld pra practi ctical cal ben benefit efitss from cli clinic nical al

ci cipl plin inee wi with th no so soci cial al agen ag enda da,, gre great er know owle ledg dgee of  evolved psychological mechanisms andater the kn environmental cues that activate them can, in principle, aid the effectiveness of preexisting widely desired social policies. Reducing the rate of child abuse, for example, could be facili facilitated tated by knowledge of the evolutionary forces that affect its occurrence. The fact that an evolutionary hypothesis led to the discovery of the single largest predictor of child abuse to date—the presence of a step-parent in the home—provides a “lever” for social policies designed to reduce the incidence of child abuse (Daly & Wilson, 2005; Herring, 2009; Jones & Goldsmith, 2005).

treatment and lifestyle recommendations.

valuable properties of evolutionary psychology and clari-

February–March 2010   American Psychologist   ●

be liable behavior if sexually a reasonable person have found the for behavior to be harassing orwould fear inducing. Evolution-guided research, however, has shown that women wom en consisten consistently tly judge a var variet iety y of act actss to be mor moree sexually harassing than do men, and women experience greater levels of fear than do men in response to specific actss of bei act being ng sta stalke lked d (Bu (Buss, ss, 2003; Duntley Duntley & Bus Buss, s, in press). But if reasonable women and reasonable men have different reactions, how exactly can a jury apply an ungendered der ed “re “reaso asonab nable le per person son sta standa ndard” rd”?? Alt Althou hough gh no firm solutions have been attained, legal scholars are beginning to evaluate evolution-based findings such as these for constructing laws that are more effective for their intended purpose, such as the reduction of illegal sexual harassment and stalking (Jones & Goldsmith, 2005). Although evolutionary psychology is a scientific dis-

8. What are the limitations of evolutionary  psychology?  Although we have articulated what we see as some of the

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fied some common misconceptions, it is also important to highlight its limitations—both empirical phenomena that are gen genuin uinely ely per perple plexin xing g and cur curren rentt con concep ceptua tuall con con-straints. One class of limitations pertains to phenomena that are truly puzzling from an evolutionary perspective, such as those that appear to reduce an indivi individual’s dual’s reproductive reproductive success, and cannot be explained by mismatches with, or hijacking of, our psychological mechanisms by modernday novel environmental inputs. The most obvious example is homosexual orientation, which has been called “the

ancest ance stor orss en enga gage ged d in hu hunt ntin ing g fo forr at le leas astt the pa past st on onee million years (Leakey & Lewin, 1992; Milton, 1999); that our ancestors lived in small groups, ranging in size from a few dozen to 150 (Dunbar, 1993); and that our ancestors made and used tools for hunting, gathering, cooking, and warfaree (Ambros warfar (Ambrose, e, 2001; Bingham, 2000; Klein Klein,, 2000). We also know that bipedal locomotion (Tattersall, 1995), extend ext ended ed chi childh ldhood ood (Ha (Harve rvey y & Clu Clutto tton-B n-Broc rock, k, 198 1985), 5), long-t lon g-term erm pai pairr bon bonds, ds, bip bipare arenta ntall inv invest estmen mentt (Ha (Hawke wkes, s, 2004), and relatively concealed ovulation (Sille´n-Tullberg ´n-Tullberg

Darwin Darwinian iandefy paradox.” parado x.” Exclu Exclusive sive since homosexual homos orientation orienta tion seems to evolutionary logic itexual presumably fails to increase an individual’s reproductive success. Although evolutionary hypotheses have been proposed for homosexuality, as discussed earlier, none have received empirical support thus far (e.g., Bobrow & Bailey, 2001). Anoth An other er pu puzz zzli ling ng ph phen enom omen enon on is su suic icid ide. e. In th thee United States, more than 30,000 individuals intentionally take their own lives each year (Gibbons, Hur, Bhaumik, & Mann, 2005). It is more common among males than females and shows age spikes in adolescence and old age. De Catanzaro Catan zaro (1995) and others (Brown (Brown,, Dahle Dahlen, n, Mills, Rick, & Biblarz, 1999) argued that suicide is most likely to occur in those who have a dramatically reduced ability to contribute to their own reproductive fitness. In several studies, they the y fou found nd tha thatt ill hea health lth,, burd burdens ensome omenes nesss to kin kin,, and

& Møller, 1993) distinguish our ancestors from their closest primate relative, the chimpanzee. Evolutionar Evolu tionary y psych psychologis ologists ts also use evide evidence nce from anthropology, archaeology, primatology, comparative biology, and ethology to elucidate some aspects of an otherwise scientifically uncertain ancestral past. For example, the paleontological evidence is rife with ancient caches of  skulls and skeletons showing patterned lethal injuries, corresponding in size and shape to ancient weapons discovered in the vicinity. When combined with cave art depictions of fighting and many other sources of evidence, the cumulative findings yield reasonable inferences that human warfare was a potent hostile force of nature for human ancestors, that males were far more often perpetrators and victims of homicide than females, and that the majority of  ancest anc estral ral att attack ackers ers wer weree rig right ht han handed ded (Du (Duntle ntley y & Bus Buss, s,

failur failure e inideati heterosexua heter osexual l mating weresomeness strong predictors torsproof  suicidal suici dal ideation. on. Although Althou gh burden burdensomen esspredic to kin vides a plausible explanation for some suicides among the elderly, it strains credulity to argue that it would be beneficial to a healt healthy hy adolescent’s adolescent’s reproductive reproductive success to end his or her life permanently, regardless of the current mating prospects. Such suicides are likely to be nonadaptive byproducts of evolved mechanisms that malfunction (Wakefield, 2005). In brief, there are puzzling phenomena such as homosexuality and suicide that remain at least somewhat inexplicable on the basis of current evolutionary psychological accounts.2 Another limitation is that we lack detailed knowledge of many selection pressures that humans faced over the millions of years of their evolution. We do not possess a videotape of deep time that would reveal in precise detail

2008). Evolutionary psychologists also use a task analysis of  existing mechanisms to provide a window into the past. Just as astronomers use phenomena such as three degree black body radiation and an expanding universe to develop cogent and testable theories about events in the universe’s past, pas t, evo evolut lution ionary ary psy psycho cholog logist istss can use the fun functi ctiona onall design of the human psychological architecture to make cogent inferences about the past. The universal and reliably developing fear of snakes, even in modern environments containing few snakes, reveals that snakes were a hostile force for ce of nat nature ure in our evo evolut lution ionary ary pas pastt (Ne (Nesse sse,, 199 1990). 0). Similar scientific inferences can be drawn from universal human taste preferences (e.g., the substances humans find bitter often conta contain in toxins toxins), ), lands landscape cape preferences preferences (e.g., desire des ire for hab habita itats ts con contai tainin ning g pro prospe spect ct and ref refuge uge), ), and mate preferences (e.g., attraction to observable cues statistically ticall y correl correlated ated with fertili fertility). ty). Humans are living fossi fossils. ls. They are walking archives that provide a wealth of knowledgee of the past. In sum edg sum,, alt althou hough gh con conver vergen gentt evi eviden dence ce from independent data sources yields especially reasonable inferences about  some   past selection pressures, evolutionary psychology, and indeed the entire field of psychology, will always be limited by incomplete knowledge of past selection pressures. A final limitation of evolutionary psychology centers on a current relative deficiency in explaining cultural and individual differences. Evolutionary psychology has been

all events over millions yearsand thatmind. have ledof tothe theselective current design of the humanofbody Nonetheless, this limitation is not total. There is a surprisingly ing ly abu abunda ndant nt amo amount unt of inf inform ormati ation on abo about ut the hum human an ancest anc estral ral env environ ironmen mentt tha thatt we do kno know w to a rea reason sonabl ablee degree of certainty. For example, ancestral humans “had two sexes; chose mates; had color vision calibrated to the spectral properties of sunlight; lived in a biotic environment with preda predators; tors; were predated on; bled when wound wound-ed; were incapacitated from injuries; were vulnerable to a large variety of parasites and pathogens; and had deleterious recessives rendering them subject to inbreeding depression sio n if the they y mat mated ed wit with h sib siblin lings” gs” (Tooby & Cos Cosmid mides, es, 2005, pp. 23–24). Scientists also know that fertilization occurred internally within females, not within males; that females, not males, bore the metabolic costs of breastfeeding; that our 122

2

Modern-day adoption of genetically unrelated children may represent another empirical puzzle; for detai detailed led discussion discussion of adop adoption tion in evolutionary perspective, see Silk (1990).

February–March 2010  American Psychologist   ●

 

far more successful in predicting and explaining speciestypicall and sex-di typica sex-differen fferentiated tiated psych psychologic ological al adapt adaptations ations than explaining variation within species or within the sexes (Buss,, 2009). Although evolut (Buss evolutionary ionary psychologists psychologists have discovered a female superiority in spatial location memory (Silverman & Choi, 2005), a likely adaptation to gathering, they the y hav havee not yet exp explai lained ned the con consid sidera erable ble var variat iation ion within women, nor why some men are better than women at this ability. Although progress is starting to occur in explaining expla ining indivi individual dual differ differences ences (e.g., Buss, 2009; Kelle Kellerr & Mill Mi ller er, , 20 2006 06;; Ne Nett ttle le,, Gangestad 2006 20 06;; Pe Penk nke e al., et al al., ., 20 2007 07)) an and d cultural differences (e.g., et 2006; Schaller & Mu Murra rray, y, 20 2008 08;; Sc Schm hmit itt, t, 20 2005 05), ), th thee fie field ld ha hass ba bare rely ly scratched the surface of the formidable task of explaining this variability.

Conclusions Over the past 15 years, evolutionary psychology has grown from being viewed as a fringe theoretical perspective to occupying occup ying a centra centrall place within psych psychologic ological al scien science. ce. Courses in evolutionary psychology are being offered at many man y col colleg leges es and uni univer versit sities ies thro through ughout out the Uni United ted States and, indeed, in countries throughout the world. Evolutionary lution ary psychology is now covered in all introductory introductory psychology textbooks, albeit with varying degrees of accuracy. One quantitative study of the coverage of evolutionary psychology in these texts came to three conclusion si ons: s: (a (a)) Co Cove vera rage ge of ev evol olut utio iona nary ry ps psyc ycho holo logy gy ha hass increa inc reased sed dra dramat matica ically lly;; (b) the “to “tone” ne” of cov covera erage ge has changed over the years from initially hostile to at least neutral neu tral (and in som somee ins instan tances ces bal balanc anced) ed);; and (c) the there re remain misunderstandings and mischaracterizations in each of the texts (Cornwell et al., 2005; Park, 2007). The purpose of this article has been to answer frequently raised questions, to clarify evolutionary psychology’s stance on controversial issues, to correct some of the more common misunderstandings, and to highlight some of its current limitations. tati ons. We hope that thes thesee clar clarifica ification tionss will increase increase the accuracy of coverage in psychology journals and textbooks, aid communication between psychologists who do and do not adopt the theoretical perspective of evolutionary psychology, and ultimately help to advance knowledge in psychological science, which is the shared goal of all psychologists regardless of theoretical perspective.

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 Appendix  Definitions of Key Terms “Mechani hanisms sms or systems of properproper Adaptation.   “Mec ties crafted by natural selection to solve the specific problems posed by the regularities of the physical, chemical, developmental, ment al, ecol ecologic ogical, al, demo demograp graphic, hic, soc social, ial, and info informat rmationa ionall environmentss encountered by ancestral populations during the environment course cour se of a spec species’ ies’ or popu populati lation’s on’s evolution” evolution” (Tooby & Cosmides, 1992, p. 62). By-products.   “Char “Characteri acteristics stics that do not solve adaptive adapt ive problems and do not have functional functional design; they are “carried along” with characteristics that do have functional design because they happen to be coupled with those adaptations” (Buss, 2008, p. 39). Cuckoldry.   Wh When en a “m “mat atee po poac ache her” r” ha hass se sex x wi with th an already alre ady marr married ied woma woman. n. Gene Genetic tic cuck cuckoldry oldry occurs when a child results from this act. Evolutionarily, a cuckolded man risks investing unknowingly in another man’s offspring. Attributes utes or componen componentt parts Design features.   Attrib of an adaptation that have been forged or “designed” by a past history of natura naturall selec selectiion tiion (no forward forward-looki -looking ng or intentional process is implied by this phrase). Evoked culture.   “Cult “Cultural ural differences differences [that] [that] are explained simply by invoking a universal shared evolved mechan mec hanism ism com combin bined ed wit with h loc local al bet betwee ween-g n-grou roup p dif differ fer-ences in input into that mechanism” (Buss, 2008, p. 417). Group selection.   “Selec “Selection tion operating operating between groups of individuals rather than between individuals. It would produce attributes beneficial to a group in competition with other groups, rather than attributes beneficial to individuals” (Ridley, 2004, p. 685). Inbreeding depression.   Occur Occurss when genetic genetic relatives together reproduce offspring that have decreased fitness due to the compounding of recessive alleles.

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the nucleotide nucleotide sequence Mutations.   Changes in the of a ge gene ne as a re resu sult lt of a co copy pyin ing g er erro rorr du duri ring ng ce cell ll division divi sion,, ultr ultravio aviolet let radi radiatio ation, n, virus viruses, es, or othe otherr muta muta-gens. Naturalisti Natur alisticc falla fallacy. cy.   The mis miscon concep ceptio tion n tha thatt ethical principles can be derived from what happens in the natura nat urall wor world. ld. Als Also o cal called led the “is “is– – oug ought ht fal fallac lacy,” y,” tha thatt because something does exist it should exist. Noise.   Ran Random dom phe phenom nomena ena pro produc duced ed by for forces ces su such ch as chance mutations, sudden and unprecedented changes in the environment, or chance effects during development. Polygenic.   An effect effect of two or more gene gene loci loci on a single phenotypic character. Paternity uncertainty.   See also cuckoldry; As a conse consequenc quencee of intern internal al female fertilization, fertilization, females can be 100% sure they are the mother of their offspring. For this same reason, males can never be 100% certain they are their offspri offspring’s ng’s father father.. Proximate Prox imate expla explanatio nation. n.   Explaining   how   a mechanism works and is implemented, which can include identi ide ntifyi fying ng how a mec mechan hanism ism dev develo elops, ps, the sti stimul mulii tha thatt activate it once it has developed, the procedures by which it operates, and the behavioral output it produces. Transmitted culture.   The subset subset of ideas, ideas, valvalues, and representations that initially exist in at least one mind that come into existence in other minds through observation or interaction (Tooby & Cosmides, 1992). Ultimate explana explanation. tion.   Exp Explain laining ing the attributes of a mechanism by identifying its evolved function, tio n, or the ad adapt aptive ive problem problem it was “design “designed” ed” by selection to solve.

February–March 2010  American Psychologist   ●