THINKING ABOUT SCIENCEM A S S I M O P I G L I U C C I

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Evolutionary psychology is themost current incarnation ofwhat started out as sociobiology,

a branch of evolutionary theory aimedat explaining the behavior of animals(and in particular, humans) as theresult of evolutionary processes, espe-cially natural selection. The turningpoint for this research program was thepublication in 1975 of Sociobiology:The New Synthesis, by Edward O.Wilson, a first-rate student of socialinsects. Wilson’s book would haveraised little controversy, if it were notfor the last chapter, where he extendedhis approach to human beings, whichhe did more fully in 1978 with his OnHuman Nature.

The debate that ensued was ideolog-ically and politically biased on bothsides, and it included ugly episodes suchas Stephen Gould publishing two nega-tive reviews of Wilson’s book (a behaviorthat borders on the unethical), and ofcourse, the famous instance of Wilsonbeing treated to a shower of cold waterand ice by an activist student attendinga scientific meeting.

On the other side of the divide,sociobiology’s cause has not been helpedby the publication of borderline intellec-tually sound works such as Herrnsteinand Murray’s The Bell Curve: Intelligenceand Class Structure in American Life,with its largely unsubstantiated claimsabout genetic determinism of humancognitive traits, and Thornhill and

Palmer’s A Natural History of Rape:Biological Bases of Sexual Coercion, whichfared only slightly better, both in con-tent and critical reception.

From a purely scientific perspective(insofar as is possible with such an emo-tionally and politically charged issue), thequestion can be asked: Is evolutionarypsychology a legitimate branch of evolu-tionary biology, or does it approximatemore the status of a pseudoscience, as itscritics have often contended? To be sure,the overarching idea that behaviors (andtherefore cognitive traits) can evolve, andsometimes do so as the result of naturalselection, is a truism that is hard to chal-lenge. The question, rather, is whether wecan have sufficient evidence that naturalselection has shaped any particularhuman behavioral pattern. To quote oneof the most preeminent critics of evolu-tionary psychology, geneticist RichardLewontin, “I must say that the best lessonour readers can learn is to give up thechildish notion that everything that isinteresting about nature can be under-stood. . . . It might be interesting toknow how cognition (whatever that is)arose and spread and changed, but wecannot know. Tough luck.”

Raising the question of whether evo-lutionary psychology is a pseudosciencein turn naturally leads us to ask what thecharacteristics of a pseudoscience are,which philosopher Karl Popper famouslyreferred to as the “demarcation prob-lem” between science and nonscience.

Unfortunately, the simple solution pro-posed by Popper, falsificationism, doesn’twork for a variety of reasons (see“Thinking about Science” May/June2004 and September/October 2004).John Casti, in his marvelous ParadigmsLost, tackles the same problem and lists aseries of characteristics of pseudosciencethat may be used as a reference point.These include anachronistic thinking,the glorification of mysteries, the appealto myths, a cavalier approach to evi-dence, an appeal to irrefutable hypothe-ses, the emphasis on probably spurioussimilarities, explanation by scenario(“story telling”), “literary” rather thanempirically based interpretations of facts,extreme resistance to revising one’s posi-tions, a tendency to shift the burden ofproof, and sympathy for a theory justbecause it’s new or daring.

Based on these criteria, the verdictfor evolutionary psychology is a mixedone. Let us take as a paradigmatic exam-ple Thornhill and Palmer’s idea that rapemay be a selected strategy for lower-ranking males to “sneak in” some repro-ductive fitness, considering that they

Is Evolutionary Psychology aPseudoscience?

Massimo Pigliucci is a professor of evolu-tionary biology at SUNY–Stony Brook, afellow of the American Association for theAdvancement of Science, and the authorof Denying Evolution: Creationism,Scientism, and the Nature of Science.His essays can be found at www.rationallyspeaking.org.

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would otherwise not have access tofemales. Regardless of how distastefulthe idea is from a moral perspective, it isof course perfectly sound from a biolog-ical one. After all, there is in fact well-documented evidence that “rape”(defined more neutrally as forced accessto females) is present in a variety of ani-mal species. The trouble starts when onelooks for corroborating evidence. Tobegin with, there is actually convincingdata out there to show that rape cer-tainly doesn’t pay as a reproductive strat-egy in today’s society. This is because ofabortion and because the risk to the per-petrator is very high. (If caught, he canbe locked away for a long time, dramat-ically reducing his chances of passinggenes to the next generation.)

Evolutionary psychologists thenresort to a typical strategy to salvagetheir theory: the modern behavior didnot evolve in response to the highlyderived current environmental condi-tions, but rather to the conditionsprevalent during the crucial period ofhuman history that occurred in the

Pleistocene. The irony here is that thisexplanation is both reasonable andessentially untestable. It is certainly rea-sonable to think that natural selectionacted for a long time in premodern pop-ulations and affected both their appear-ance and behavior; on the other hand,unfortunately, behaviors have an annoy-ing tendency not to leave a fossil record,and neither do the details of the (largelysocial and cultural) environment underwhich natural selection allegedly oper-ated throughout recent human evolu-tion. This makes resorting to Pleistocenescenaria a “just-so story,” with very littlescientific content or relevance.

The other major route available toevolutionary psychologists is the so-called comparative method, i.e., the pos-sibility to study the evolution of a char-acteristic by comparing a focal species(humans) to their close relatives (thegreat apes). But once again, we run intothe same problem that, while thisapproach is indeed widely used in evolu-tionary biology, it simply doesn’t work inthe case of our own species. The reason is

another unfortunate accident of history:for the comparative method to workproperly, one needs many closely relatedspecies to compare (to achieve statisticalpower). Alas, we have only a handful ofliving relatives (one or two species ofchimps, and one or two of gorillas), andthey are actually separated from us byseveral millions of years of independentevolution. As Lewontin remarked, itwould be nice to know, but it looks likewe simply don’t have enough historicaltraces to make much progress.

While all of this doesn’t make evolu-tionary psychology a typical example ofpseudoscience, say like astrology orparapsychology, it certainly moves itaway from mainstream evolutionarybiology and into a territory uncomfort-ably close to purely historical research,where reasonable scenaria are the bestone can hope for and hard data are dif-ficult to come by or interpret. DidNapoleon lose at Waterloo because hehad indigestion and was not feeling toowell? It’s a reasonable hypothesis, but wearen’t likely to find out. !

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