The new science of evolutionary psychology has generated considerable controversy since its rise in the 1990s, with critics and proponents taking shots at one another. Skeptic magazine devoted an issue to the controversy in 1996 (Vol. 4, No. 1), and in 2005 a major critique was published in book form by MIT Press. In Skeptic Vol. 12, No. 1, we ran an excerpt from this book, by David Buller, with a reply to it from Frank Miele, which follows here.
Adaptationism pervades every level of biological inquiry, and always has, because at every level descriptions of relevant phenomena are almost invariably functional descriptions. The only scientifically coherent account of the origin of adaptations, and hence the only scientifically coherent account of ‘function’, is evolution by selection.
— Donald Symons
The opening motions in philosopher David J. Buller’s case against Evolutionary Psychology (EP) appeared on his web site,1 followed by the major argument in his book, Adapting Minds.2 More recently, Buller argued against leading evolutionary psychologists John Tooby and Leda Cosmides, Martin Daly and Margot Wilson, and David Buss in the journal Trends in Cognitive Science (TCS), which allowed them to respond to Buller’s critique.3 In his Skeptic article in this issue, Buller takes his case to a more popular jurisdiction. His brief against EP has two parts:
- A general critique of the concept of the modular (“Swiss Army Knife”) model of the mind, which he describes as a core dogma of EP. If this foundation crumbles, the entire edifice of Evolutionary Psychology will fall.
- A specific critique of the data used to support two “signature achievements” of EP: Martin Daly and Margot Wilson’s Cinderella Effect; and David Buss’s studies of male-female differences in jealousy.
This article reviews the arguments and data for and against Evolutionary Psychology, Buller’s criticisms, and the responses to them.
How Modular is the Mind? Debate, Not Dogma
David Buller is “deeply skeptical” of what he calls EP’s two “defining doctrines.” First, that the human mind is “massively modular,” composed of a myriad of independent, special purpose (“domain-specific”) modules, each evolved to help our ancestors survive and reproduce during the hunter-gather period of human evolution. Second, that no subsequent cognitive adaptations to novel environments have occurred. According to Buller, evolutionary psychologists think that we are “a legion of idiot savants” who struggle to get by like “Fred and Wilma Flintstone” dumped out of a time machine into modern suburbia.
Modularity and adaptation to novel environments are two of the central debates, not dogmas, in EP. They are described in the textbook by David Buss, one of the evolutionary psychologists whose work Buller claims to have refuted. Interestingly, Buller cites Buss’s first edition, but not the second (2004), which updates the coverage of these issues.
The view that “humans must possess a large number of specialized psychological mechanisms, each dedicated to solving specific adaptive problems,” Buss summarizes, is “widely accepted within the field of evolutionary psychology and indeed lies at the foundation of evolutionary approaches.” However, he then quotes several evolutionary psychologists who have “recently argued that in addition to these specific mechanisms humans also have evolved several domain-general mechanisms.” His list of such general purpose processes includes: “intelligence, concept formation, analogical reasoning, working memory, and classical conditioning.” Finally, Buss notes that we “routinely solve ancient adaptive problems in highly novel ways” and that “everyone recognizes that humans have been able to flourish in an environment very different from that in which we evolved.”
While he concludes that the specificity–generality debate remains an open question, Buss emphasizes that no evolutionary psychologist has ever claimed that domain-specific modules are hermetically sealed off from each other by any neurocognitive firewalls. Rather, discovering “the precise nature of information sharing” between modules lies at the cutting edge of research.4
CSI Cinderella — Buller’s Critique of Daly & Wilson
Evolutionary psychologists Martin Daly and Margot Wilson have spent over two decades studying the nature of nurturing from an evolutionary viewpoint. Based on Darwinian theory they hypothesized the “Cinderella Effect” — children living with stepparents would be far more likely to be abused than would children living with both genetic parents. They reasoned that in species like ours that provide substantial parental care, evolution would select for nurturing behavior that was directed toward genetic, rather than non-genetic, children in order to increase their odds of reaching maturity and reproducing. In the cold evolutionary calculus of Richard Dawkins’ proverbial selfish gene, “Why invest in a competitor’s product?” All other things being equal, the greater the degree of genetic relatedness, the greater probability of helping and the lesser the probability of hurting someone else. Neither Daly and Wilson nor any other evolutionary psychologists have ever argued that this is the only factor causing child abuse. Rather, they say it is the major factor in explaining human parenting. Nor have they denied the role played by socioeconomic or cultural factors, but instead have documented them.
The Cinderella Effect for lethal, non-lethal, and sexual abuse has been verified not only by Daly and Wilson and their students, but by other researchers as well, working in different countries, applying various statistical methods and experimental designs, to a number of independent datasets. On the flip side, selective caregiving to genetic children over stepchildren has been documented as well. Daly and Wilson have summarized just some of the research supporting the Cinderella Effect in their responses to Buller, which I recapitulate here.5
- From infancy on, stepchildren suffer higher lethal and nonlethal accident and injury rates, probably because they are less watched over and protected.
- Stepchildren leave home at a higher rate, at a younger age, and more often give family conflict as their reason.
- Parents were five times more likely to provide their genetic children with money for college than their stepchildren.
- In Britain, both mothers and stepfathers expressed even lower aspirations for their stepchildren’s education than did poorer single mothers.
- Stepchildren in Dominica suffer reduced growth and higher stress hormone levels than age mates living with their genetic parents in the same village and material conditions.
- In Trinidad, village stepfathers spend significantly less time with their children than genetic fathers and many more of their interactions are nasty.
- Hunter-gatherer stepfathers in Tanzania watch over their stepchildren in camp, but unlike genetic fathers, never play with them.
Buller lists three “serious shortcomings” in the research by Daly and Wilson. Together, he says, they “conspire to cast doubt” on the reality of the Cinderella Effect.
First, Buller states that while the best evidence for the Cinderella Effect comes from their “landmark 1985 study,” Daly and Wilson went wrong by lumping physical abuse, sexual abuse, and neglect together into a single category of abuse. He counters their results with those from his own analysis of the Third National Incidence Study of Child Abuse and Neglect (NIS-3). While Daly and Wilson found that children under five who lived with a genetic parent and a stepparent were 40 times more likely to suffer abuse than those living with both genetic parents, his NIS-3 data show that they were only 3.3 times more likely to be abused. Buller concedes that this still shows a Cinderella Effect, but a much smaller one. (Note, however, Daly and Wilson’s data are from Canada, Buller’s from the U.S. Reporting procedures and protocols are quite different in the two countries.)
Next, Buller criticizes the fact that Daly and Wilson analyzed their data by households, not by identity of the perpetrator. The NIS-3 data do. How can we be sure that the abuse in the Canadian studies was really committed by the stepfathers and not the genetic mothers? (It’s much less common for children to live with their genetic fathers and stepmothers). This allows Buller to expose what he says is “a clear anomaly for Daly and Wilson’s hypothesis, single genetic fathers were 1.7 times more likely than stepfathers to physically abuse their children.” (Rightmost column in Buller’s Table 5: 11.4/6.8 ≈ 1.7).
Were Daly and Wilson unaware of the issue of failing to ID the perps or the increased risk of abuse for children living with only one genetic parent? Have they avoided them in order to bolster the Cinderella Effect? Clearly not. Both are spelled out in an article that Daly and Wilson published as far back as 1981!6
First they explain that:
We present the data in terms of household composition rather than perpetrator for several reasons. While stepparents are relatively frequent perpetrators of abuse, so to a lesser extent are natural parents with stepparent spouses. The labelled “perpetrator” is not necessarily the instigator, and moreover, one party may assume responsibility to protect another. In the case of neglect, identification of a single perpetrator seems inappropriate. For these reasons, household composition is the more reliable datum.7
In this 1981 article, Figure 24–1 clearly shows that “Father-only is much the riskiest situation.”8 To my knowledge, Daly and Wilson were the first to document this. As they state in their abstract, while socioeconomic, psycho–pathological, and developmental factors all play a role in explaining child abuse, “an evolutionary perspective may provide a more encompassing view of circumstances exacerbating the risk of abuse and neglect and of the ultimate rational for variations in parental solicitude and negligence.”9
While conceding that his own analysis of the NIS-3 data “does appear to confirm” (emphasis added) the Cinderella Effect, Buller’s third criticism is that the officials who investigate abuse cases are biased in attributing blame to stepparents while tending to dismiss charges against biological parents. He supports this argument with the results of a Colorado study, which showed that child fatalities caused by abuse at the hands of “other relatives” (including stepfathers legally married to the genetic mothers) were “1.37 times more likely to be recorded as the result of maltreatment on death certificates” than were those for genetic parents. This bias in reporting, Buller argues, is sufficient to account for the mild Cinderella Effect that appears to be present in the NIS-3 data.
Then where are the dead bodies? Daly and Wilson reply that if stepfathers were always caught while genetic fathers usually get away with it, “there would have to have been more than 500 undiscovered paternal murders [in Canada] each year,” above the average of 4 that are detected, to make the two rates equal. In fact, “fewer than 400 Canadian children under 5 years of age died annually in 1974–1990 from all causes other than diseases and congenital abnormalities.”10
In his response to Daly and Wilson’s defense, Buller falls back on saying that his argument “was not that bias in U.S. data accounts for overrepresentation in Canadian or other data, but that overrepresentation in those data may be found to be an artifact of recording if empirical research into bias, such as that of the Colorado study, were conducted.”11 However, the amount of bias required in the Canadian data would have to be enormous.
Other lines of evidence provide additional support for the Cinderella Effect. Victim self report studies show a higher percentage of abuse attributed to stepparents than to genetic parents. And stepparents themselves report that they experience less parental love toward stepchildren than they do toward genetic children. For Buller’s critique to hold up, all of these lines of independent evidence would have to be similarly biased. This is possible, but not probable.
The Case of the Green-Eyed Monster(s): Buller’s Critique of Buss
David Buss and his colleagues have studied the Darwinian basis of mating, conflict between the sexes, social status, homicide, and jealousy.12 Buller concentrates his attack on jealousy.
Buss predicted that “because reproductive consequences of infertility and partner loss for males and females are parallel in some respects, and asymmetric in others,”13 they would be similar in some respects, but different where evolution presented them with different problems. They would differ because, “males risk both lowered paternity probability and investment in rival gametes if their mates have sexual contact with other males,” while females “do not risk lowered maternity probability through partner infidelity, but they do risk the diversion of their mate’s commitment and resources to rival females.”14
For a male, being a cad isn’t so bad, but being cuckolded definitely is. “It is a wise father who knows his own child.” For a female, however, “maternity is a certainty,” so being left holding the baby by a deadbeat dad is definitely bad, especially if his resources are being squandered dallying with Dolly.
In their TCS response to Buller, Buss and co-author Martie Haselton list four ways males and females were predicted to be similar, and 13 ways in which they were predicted to be different. Derived from Darwinian theory, they have all been tested and confirmed.15
Boxes 1 and 2 in Buller’s article here summarize the critical male-female difference — the response to sexual versus emotional infidelity. In every case, males were more upset than females by the sexual scenario. Buller does not question the data, only Buss’s conclusion. Confirming the evolutionary explanation requires evidence that males become more upset about sexual infidelity than they do about the emotional unfaithfulness.
In his TCS reply, Buss notes that he and his colleagues “were careful to state the prediction not in terms of absolute levels of jealousy, which are affected by many factors external to the hypothesis, but rather in sex differences in sensitivities to different forms of infidelity.”16 Buller retorts that this is “retrofitting their predictions to the data.”17 Is it?
In 1992, Buss et al. wrote that their “central hypothesis” derived from Darwinian theory was that both sexes should be distressed over both sexual and emotional infidelity but that the “two kinds of infidelity should be weighted differently by men and women.”18 (Emphasis added.) In 1999, Buss emphasized the point that, “Both sexes, of course, are distressed by both forms of infidelity, and the evolutionary hypothesis suggests that they should be, given their correlated nature in everyday life….The hypothesis, rather, is about sex differences in the emotional weighting of the aspects of infidelity.”19 (Emphasis added.) Buss’s original reasoning may not satisfy Buller, but his response is hardly “retrofitting.”
Buller cites a study that shows that males are more physiologically aroused than females by sexual content generally which, he says, “Buss himself had admitted would undermine his theory.” What Buss actually wrote is that future research “could profitably explore” their correlation.”20 And what, if not adaptation, explains the greater male arousal? While cultural factors play some part, Buss and his colleagues have not denied them, but documented them.21
Buller offers an alternative to the evolutionary explanation, which he dubs “the relationship jeopardy hypothesis.” It says the sex difference is “a product of typical differences in the information believed by the sexes, not of a sex difference in the design of the mechanisms that process that information.” This “belief hypothesis” is based on the research of DeSteno and Salovey.22 Evolutionary psychologists are hardly ignorant of it. The 1999 paper by Buss et al., which Buller cites, addresses their methodological critique of the evolutionary hypothesis and details the conceptual difficulties with the belief hypothesis. Finally, it describes the results of four experiments that pitted the two against each other and found “the belief hypothesis is not well supported.”23 Like the Cinderella Effect, the sex difference in jealousy has been confirmed by other researchers, in different countries, applying various experimental designs and statistical methods to a number of independent datasets.
Conclusion: Cased Dismissed
In his case against Evolutionary Psychology, Buller misses — or skillfully avoids — the big picture. The interesting, though by no means novel, points he makes fit Richard Dawkins’ description of earlier such criticisms as “a catalogue of methodological shortcomings of particular studies.”24
Buller fashions his arguments like a defense attorney in a criminal case. He attempts to sow doubt regarding this or that piece of evidence, or to offer alternative interpretations as to what might have happened. The scientific method, however, is like a civil case, where the standard is not “beyond a reasonable doubt” but rather “the preponderance of evidence.” Moreover, a civil case does not require an either-or verdict of “guilty” or “not guilty;” rather, liability can be apportioned. Likewise, in the behavioral sciences especially, a good theory or hypothesis need not explain everything, but only provide the simplest and most coherent explanation.
Evolutionary psychology satisfies philosopher Imre Lakatos’ criterion that true science is “progressive.” It has proven able “to ‘digest’ (successfully account for) apparent anomalies and generate novel predictions and explanations” and therefore has “the hallmarks of a currently progressive research program capable of providing us with new knowledge of how the mind works.”25 A glance at the recently published Handbook of Evolutionary Psychology26 (edited by David Buss) shows just how vigorous and productive the field is.
Important challenges remain, however. The most important are determining the role of domain-specific versus domain-general processes27 and integrating evolutionary psychology, behavior genetics, neurosciences, and psychometrics.28
The critics notwithstanding, Evolutionary Psychology is here to stay.
- Buller, D. J. 2005. Adapting Minds: Evolutionary Psychology and the Persistent Quest for Human Nature. Cambridge, MA: MIT Press.
- In addition to Buller’s web site see http://www.psych.ucsb.edu/research/cep/buller.htm for the TCS responses by Tooby & Cosmides, Daly & Wilson, and Buss.
- Buss, D. M. 2004. Evolutionary Psychology: The New Science of the Mind. pp. 56–57. NY: Pearson.
- For detailed descriptions of the original studies and citations to them see Daly & Wilson’s web page (http://psych.mcmaster.ca/dalywilson/research.html) that also contains their classic article, “The ‘Cinderella Effect’: Elevated Mistreatment of Stepchildren in Comparison of Those Living with Genetic Parents” as well one of their replies to Buller. Another reply by Daly & Wilson appears in the journal, Trends in Cognitive Sciences in November 2005.
- Daly, M. and M. I. Wilson. 1981. “Abuse and Neglect of Children in Evolutionary Perspective.” In Alexander, R. D. and D. W. Tinkle. (Eds.). Natural Selection and Social Behavior. NY: Chiron Press, pp. 405–416.
- Ibid. p. 408.
- Ibid. p. 409.
- Ibid. p. 405.
- Daly, M. and Wilson, M. 2005. Reply to David Buller. http://psych.mcmaster.ca/dalywilson/research.html, p. 1
- Buller, D. J., J. Fodor, and T. Crume. 2005. “The Emperor is Still Under-Dressed.” Trends in Cognitive Science. (forthcoming), p. 2.
- Buss, D. M. and M. Haselton. 2005. “The Evolution of Jealousy: A Reply to Buller.” Trends in Cognitive Science. November. p. 1. (http://homepage.psy.utexas.edu/homepage/Group/BussLAB/pdffiles/buss_haselton_reply_to_buller.doc)
- Buss, D.M., R. J. Larsen, W. Westen, and J. Semmelroth. 1992. “Sex Difference in Jealousy: Evolution, Physiology, and Psychology.” Psychological Science. Vol. 3 No. 4. p. 251.
- Buss and Haselton, 2005, pp. 1–2.
- Ibid., p. 3.
- Buller, Fodor, and Crume, 2005, p. 1.
- Buss et al., 1992, p. 251.
- Buss D. M., T. K. Shackelford, L. A. Kirkpatrick, J. C. Choe, H. K. Lim, M. Hasegawa, T. Hasegawa, and K. Bennett. 1999. “Jealousy and the Nature of Beliefs about Infidelity: Test of competing Hypotheses about Sex Differences in the United States, Korea, and Japan.” Personal Relationships. Vol. 6 No. 4, pp. 125–126.
- Buss et al., 1992, p. 255.
- Buss et al., 1999, pp. 139–146.
- DeSteno, D. A., and P. Salovey. 1996. “Evolutionary Origins of Sex Differences in Jealousy?” Psychological Science Vol. 7, pp. 367–372. DeSteno, D. A., and P. Salovey. 1996. “Genes, Jealousy, and the Replication of Misspecified Models.” Psychological Science Vol. 7, pp. 376–377.
- Buss et al., 1999, p. 148.
- Dawkins, R. 2005. “Afterword.” In Buss, D. M. The Handbook of Evolutionary Psychology. NY: Wiley, pp. 977–978.
- Ketellar, T., and Ellis, B. J. 2000. “Are Evolutionary Explanations Unfalsifiable? Evolutionary Psychology and the Lakatosian Philosophy of Science.” Psychological Inquiry. Vol. 11. No. 1. p. 2.
- Buss, D. M. 2005. The Handbook of Evolutionary Psychology. NY: Wiley.
- Buss, D. M. 2004, pp. 56–57.
- Bailey, J. M. 1997. “Are Genetically Based Individual Differences Compatible With Species-Wide Adaptations?” In Segal, N. L., G. E. Weisfeld, and C. C. Weisfeld. (Eds.) Uniting Psychology and Biology. Washington, D.C.: American Psychological Association, pp. 81–100. Segal, N. L., and K. B. MacDonald. 1998. “Behavior Genetics and Evolutionary Psychology: A Unified Perspective on Personality Research.” Human Biology. Vol. 70, pp. 159–184.
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