Evolutionary psychology questions answered, Part 1

Back on December 13th I asked readers to submit questions and promised to answer at least the top five (by votes). I am impressed with the great questions that have been posted since and I will try to do them justice. I will take the first in this post, and only the first because it’s a very broad question.

What are the most notable confirmed and disconfirmed hypotheses from the field of EP, and which of these do you consider most representative of the field operating properly as a scientific endeavour? 7 votes, submitted by Damion Reinhardt.

“Notable” is somewhat subjective, and I will remind readers that “confirmed” is here used in the scientific sense that there is adequate evidence from multiple studies and replications to reasonably take as correct. Biologist Jerry Coyne, known for the Why Evoltuion is True (book and website), makes a fairly good list and I agree to most of these:

Incest avoidance, especially in those societies that haven’t made a connection between incest and birth defects. Also, the proximate cues for avoiding incest, as in the failure of children raised in a kibbutz to marry.

Humans’ innate fear of harmful creatures or features, as in spiders and heights, and the lack of innate fears of more modern dangers.

The variance in offspring number between males and females in various societies, and the differential “pickiness” of males and females when choosing mates

The evolution of concealed ovulation in humans as opposed to other primates.

The use of odors and immune-system matching (i.e., MHC genes) as cues for mates.

The cause of sexual dimorphisms (e.g., size differences between males and females).

The cause of physical and physiological differences between human ethnic groups (was it sexual selection, drift, or something else?)

Gene-culture coevolution, as in the evolution of lactose tolerance.

The evolution or morality using comparative studies with other primates.

Parent-offspring conflict, and cases in which kin are favored over nonkin

Why we like food that is bad for us (e.g. fats and sweets), and why we feel disgust at certain foods or odors

Let me expound on a few of these for the unfamiliar. Research shows that a fear of snakes is common across humanity and in many primates. People who grew up in the inner city and have never seen a snake “in the wild” are nonetheless afraid of them. The same humans are not afraid of automobiles, despite them being far more likely to hurt or kill them and despite many having experienced this or know friends who did. This is substantial evidence that some fears are not learned. Experimenters have noted this in labs as well, wherein monkeys raised in said labs are afraid of snake-shaped tubes having never seen a snake in their lives.

Kin selection is an hypothesis that people favor apparent blood relatives over non-blood relatives in a wide variety of ways. This hypothesis has an incredible volume of statistical data in support. Affinity, affection, and the likelihood of bestowing favors are attenuated by apparent genetic relatedness. On the negative side, murder directed at blood kin is quite rare compared to such acts between non-kin.

Evolutionary psychologist Rob Kurzban produced a list of studies he believes Coyne may have been referring to. Here is Rob’s list for further reading (I would also encourage readers to check out his excellent EP blog):

Incest Avoidance

Fessler, D. M., & Navarrete, C. D. (2004). Third-party attitudes toward sibling incest: Evidence for Westermarck’s hypotheses. Evolution and Human Behavior, 25(5), 277-294.

Lieberman, D. (2009). Rethinking the Taiwanese minor marriage data: evidence the mind uses multiple kinship cues to regulate inbreeding avoidance. Evolution and Human Behavior, 30(3), 153-160.

Lieberman, D., & Symons, D. (1998). Sibling incest avoidance: from Westermarck to Wolf. Quarterly Review of Biology, 463-466.

Lieberman, D., Tooby, J., & Cosmides, L. (2003). Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest. Proceedings of the Royal Society of London. Series B: Biological Sciences, 270(1517), 819-826.

Lieberman, D., Tooby, J., & Cosmides, L. (2007). The architecture of human kin detection. Nature, 445(7129), 727-731.

Fear of Spiders etc.

Gerdes, A., Uhl, G., & Alpers, G. W. (2009). Spiders are special: fear and disgust evoked by pictures of arthropods. Evolution and Human Behavior, 30(1), 66-73.

Nesse, R. M. (1994). Fear and fitness: An evolutionary analysis of anxiety disorders. Ethology and Sociobiology, 15(5), 247-261.

Öhman, A. (1986). Face the beast and fear the face: Animal and social fears as prototypes for evolutionary analyses of emotion. Psychophysiology, 23(2), 123-145.

I will add a couple here (-Ed)

D.H. Rakison, J. Derringer (2008). Do infants possess an evolved spider-detection mechanism?

Cognition, 107 (2008), pp. 381–393

M. Cook, S. Mineka. (1990). Selective associations in the observational conditioning of fear in rhesus monkeys. Journal of Experimental Psychology: Animal Behavior Processes, 16, 372–389.

MHC genes and mating

Herz, R. S., & Inzlicht, M. (2002). Sex differences in response to physical and social factors involved in human mate selection: The importance of smell for women. Evolution and Human Behavior, 23(5), 359-364.

Penn, D. J., & Potts, W. K. (1999). The evolution of mating preferences and major histocompatibility complex genes. The American Naturalist, 153(2), 145-164.

Roberts, S. C., Little, A. C., Gosling, L. M., Perrett, D. I., Carter, V., Jones, B. C., … & Petrie, M. (2005). MHC-heterozygosity and human facial attractiveness. Evolution and Human Behavior, 26(3), 213-226.

Sexual Dimorphism

Penton-Voak, I. S., Little, A. C., Jones, B. C., Burt, D. M., Tiddeman, B. P., & Perrett, D.I.(2003). Female condition influences preferences for sexual dimorphism in faces of male humans (Homo sapiens). Journal of Comparative Psychology, 117(3), 264.

Puts, D. A., Gaulin, S. J., & Verdolini, K. (2006). Dominance and the evolution of sexual dimorphism in human voice pitch. Evolution and Human Behavior, 27(4), 283-296.

Thornhill, R., & Gangestad, S. W. (2006). Facial sexual dimorphism, developmental stability, and susceptibility to disease in men and women. Evolution and Human Behavior, 27(2), 131-144

Parent-offspring conflict

Buunk, A. P., Park, J. H., & Dubbs, S. L. (2008). Parent-offspring conflict in mate preferences. Review of General Psychology, 12(1), 47.

Rohde, P. A., Atzwanger, K., Butovskaya, M., Lampert, A., Mysterud, I., Sanchez-Andres, A., & Sulloway, F. J. (2003). Perceived parental favoritism, closeness to kin, and the rebel of the family: The effects of birth order and sex. Evolution and Human Behavior, 24(4), 261-276.

I would add to these Life History Theory and Social Contract Theory. Both require essays of their own to properly explain but I will give them a very brief summary.

Life History Theory (LHT) is a biology theory about how organisms allocate their resources over their complete lifespan. A central idea is the timeline for reproduction based on environmental conditions: is it better to reproduce early, or to shore up bodily resources to do so later? LHT originated in the study of animal behavior, but has tremendous import for humans and human society. It is hypothesized that environmental cues to instability and unpredictability change human behavior such that investment in immediate reproduction becomes a more urgent priority and self-investment such as education or insurance, less so. The logic of this is very simple: why save up for later if you aren’t sure there is going to be a later? This is one of many examples of how tightly integrated the understanding and effects of culture are to evolutionary psychology theory. In recent years, LHT as it applies to evolutionary psychology has been best articulated and developed by AJ Figueredo. Here are two papers on the subject:

Figueredo et al., 2006 Consilience and life history theory: From genes to brain to reproductive strategy. Developmental Review, 26 (2006), pp. 243–275

Figueredo et al., 2005 The K-Factor: Individual differences in life history strategy

Personality and Individual Differences, 39 (8) (2005), pp. 1349–1360 Link

Social Contract Theory

A part of a cognitive program for successfully navigating a social landscape among others we must both cooperate with and compete with, we should have specializations for social interactions that prevent our exploitation and secure fair outcomes. This is SCT in a nutshell. SCT has every virtue that I think an evolutionary psychology theory could have:

It is grounded in a venerable body of literature about the evolution of cooperation and altruism, see George Williams & game theory

It is a clear theoretical model, well defined and easily parsed

The implications of the model have been tested, both among Americans and non-western cultures

Several alternative explanations for the above results have been tested and ruled out

A locus (or rather two locii) in the brain itself has been located that, when damaged, severely impairs SC ability, while leaving almost all other cognitive abilities intact. This points to likely physical locations of the SC module in the brain

See a full discussion extensive citations in chapter 3 of The Adapted Mind by Jerome Barkow, Leda Cosmides and John Tooby.

Disconfirmed hypotheses?

Most failed hypotheses die a quiet death of attrition because failure to show an effect or failure to replicate usually means a study is not publishable. This is known as the file drawer effect. I can only think of one “notable” such hypothesis. In the late 90’s the notion that homosexuality, particularly among men, might be explained in terms of kin selection if said males invest substantially in their close genetic relatives versus straight males. However, studies failed to find evidence that such a disparity exists. See:

David Bobrow, J.Michael Bailey. 2001. Is male homosexuality maintained via kin selection? Evolution and Human Behavior 22-5. 361–368.

The hypothesis has been overshadowed by more promising research. For example, check out the current Quarterly Review of Biology which contains a paper about the epigenetic developmental theory of homosexuality. I believe it is freely viewable. Here’s the citation:

William R. Rice, Urban Friberg and Sergey Gavrilets. 2012. Homosexuality as a Consequence of Epigenetically Canalized Sexual Development. The Quarterly Review of Biology . 87-4, 343-368.

Although not “notable” it is worth mentioning that the casting out of evolutionary psychology hypotheses is something that I see all the time. Usually, this happens in early stages, such as when a colleague is proposing a research plan (or when I have) and a cohort either points to contradictory research or finds a flaw in their theoretical approach. Sometimes it happens after data has been collected in an initial “test the waters” study, and the data do not support the hypothesis. Note that all of these are examples of peer and evidence-based rejection before formal peer review comes into play (which only happens after submission to a journal for publication). The popular notion among inexperienced critics that any “just so story” passes muster is an absurd fantasy.