Thursday, October 20th 2011
Mate magnet madness: when the range of possible explanations exceeds your own hypothesis
This blog post first appeared on my blog on March 4th, 2011. I’m sharing it with the Scientific American audience today because I’ve assigned this post to my students for next week. Plus, who doesn’t love a good John Tierney takedown?
My daughter will be three in just a few weeks. She loves telling stories. These stories have the same, uncomplicated arc every time: she and her friends Dora, Diego, Boots and Baby Jaguar go on an adventure to rescue Mommy from the giant condor. Or sometimes Mommy and Dora and Diego and Boots and Baby Jaguar are rescuing her. Or sometimes Daddy does the rescuing.
There is almost always a net, then a pair of Rescue Scissors needed to cut the captive free. But the variation in these stories is very small, the framework borrowed heavily from one of the few mythologies known to my little girl: Dora the Explorer.
Evolutionary psychology is often a kind of story-telling, and instead of borrowing from a preschool cartoon they borrow from the concept of anisogamy. Anisogamy is sexual reproduction formed by unequal gametes, in our lineage a big egg made by females and little sperm made by males. This provides the foundation for differential reproductive investment, where females often put in the time and effort of gestation, lactation and care. From here, proponents of EP see essential differences between what men and women want in relationships, and the kinds of relationships that are optimal, and a model this broad makes it possible to shoehorn any behavior into its adaptive framework.
Enter John Tierney, my (not) favorite journalist for the New York Times. This is the man who thinks that sexism is a radical act (I am referring to his charming articles on gender disparities in science). So I suppose I shouldn’t have been surprised when he outed himself as an EP fanboi in his most recent piece, “The Threatening Scent of Fertile Women.”
Tierney covered the work of Jon Maner and others who have studied relationship maintenance – the suite of behaviors that keeps a couple together. In particular, Tierney focuses on the problem of the wandering eye, or rather, the possible mechanisms that prevent it in a monogamous couple. The idea here is that relationship maintenance is evolutionarily adaptive, because when a couple stays together it is easier to raise offspring and increase reproductive success.
The range of explanations
The study that frames Tierney’s column is Miller and Maner (2010). Thirty eight undergraduate men rated the attractiveness of a woman with whom they interact, at several points over her menstrual cycle. The authors found NO relationship between where a woman is in her cycle and how attractive a single man finds her, but a negative relationship between the chance a woman is fertile and how attractive a partnered man finds her.
What do Miller and Maner (2010) discuss, and what is the idea Tierney is so enamored with?
“It’s possible that some of the men in Florida were just trying to look virtuous by downgrading the woman’s attractiveness, the way a husband will instantly dismiss any woman pointed out by his wife. (That Victoria’s Secret model? Ugh! A skeleton with silicone.) But Jon Maner, a co-author of the study, says that’s unlikely because the men filled out their answers in private and didn’t expect the ratings to be seen by anyone except the researchers.
“It seems the men were truly trying to ward off any temptation they felt toward the ovulating woman,” said Dr. Maner, who did the work with Saul Miller, a fellow psychologist at Florida State. “They were trying to convince themselves that she was undesirable. I suspect some men really came to believe what they said. Others might still have felt the undercurrent of their forbidden desire, but I bet just voicing their lack of attraction helped them suppress it.””
This conjecture is unconnected to the study’s methodology and results. Nowhere in that study did they assess the participants’ state of mind or ask them how they felt about this. How do we know they were trying to convince themselves of anything? This finding, while interesting, does not test their hypothesis for an evolutionary framework for relationship maintenance that includes adaptively suppressing attraction to others.
Maner et al (2009) studied the attention people pay to images of attractive people of the opposite sex when first exposed to sexual words like “lust” and “kiss.” They recruited 120 straight undergraduates, thirty six of whom were in committed relationships. Individuals in committed relationships paid far less attention to the attractive images than those not in relationships. Tierney titters,
“The subliminal priming with words related to sex apparently activated some unconscious protective mechanism: Tempt me not! I see nothing! I see nothing!”
I’ve done my own share of human subjects research, and subjects will often tell you or do what they think you want, or they will just not be honest if they don’t want you to know the truth. What if, as originally posed by Tierney himself, the respondents weren’t warding off temptation but wanted to look virtuous? What if, now bear with me because this might seem crazy, the people in these studies were in love with their partners and genuinely uninterested in anyone else? Too often EP wants to provide a single explanation for a behavior, when the range of possible explanations far exceeds their hypothesis.
An anthropological perspective
Jamie Jones, Associate Professor at Stanford and blogger at Monkey’s Uncle describes anthropology like this,
“…[A]nthropology is the science charged with explaining the origin and maintenance of human diversity in all its forms. To achieve this end, anthropology must be unapologetically grand in its scope. How can we explain human diversity without documenting its full extent, through both time and space, and across cultures? … Where does the tapestry of human diversity come from and how is it that we continually manage to resist powerful homogenizing forces and hang on to our diversity? What commonalities transcend local difference to unite all humanity? How is it that civilizations rise and fall? And what is the fate of humanity?”
Jamie beautifully depicts the importance of documenting and understanding diversity even in the face of efforts to simplify human nature. Thus, to me, an anthropological perspective is often at odds with EP explanations for behavior.
An anthropological perspective asks, what happens if you take these basic observations and, instead of deciding on a favorite explanation and applying it to everyone, put them into a model in which you can vary context (age/sex specific mortality rates, distribution of resources, what have you) and see what range of strategies actually give fitness benefits? That is, when you actually throw some variation into the equation, is this still the best strategy for the partnered men with whom Tierney feels simpatico?
Right now we don’t know. Much psychological empiricism rests on undergraduates who participate in studies for course credit. When one wants to make connections to evolutionary adaptedness, they may be a place to start, but not end.
I have a real problem with continuing to use this population to make statements of universality for all humans. Undergraduates usually are trying to avoid pregnancy and build their financial and social capital, so relationship maintenance for the sake of reproductive success rarely exists. Until we can show that relationship maintenance, and the particular behaviors Miller, Maner and others study within that are shown across many populations, and particularly across reproductively-aged folks, their argument for adaptation fails.
Another problem is that most work on relationships in EP tends to be heteronormative, meaning that they think nothing of assuming that either everyone is straight, or the universally best behavioral strategy is to be straight. They also tend to assume that the best strategy is to be monogamous, with occasional sneaky infidelity permitted if one can get better genes or more offspring that way (keep in mind that there is a difference between what might be biologically advantageous in a certain context, and what is culturally appropriate – the argument here is not against the culture of monogamy).
But heterosexual monogamy is only one reproductive strategy of many that humans employ. Depending on how you measure it, monogamy and polygyny (single male, multi female marriage) vie for the most frequent strategy – in fact, polygyny occurs in about 80% of modern human societies (Murdock and White 1969). There are even a few rare populations that practice polyandry, which is the marriage of a single female and multiple males. And, even in those populations where monogamy is practiced, serial monogamy is far more frequent than lifetime monogamy: this means that individuals have a series of monogamous relationships rather than find one mate for life (so no, divorce is not a modern human invention).
When taking an even broader, comparative perspective, monogamy isn’t practiced by our closest relatives at all. Chimpanzees and bonobos, both equally related to us, are promiscuous. This is a scientific term for a reproductive strategy that involves females and males making reproductive decisions to mate with many individuals at each fertile period. Bonobos are also promiscuous, but they also use heterosexual and homosexual sex to reduce stress and aggression, and form bonds among one another. Gorillas, our next closest relative, are polygynous. Orangutans are very solitary, but essentially promiscuous. It’s only once you delve into the lesser apes, the gibbons, that you see any monogamy, and they are far less monogamous than we first thought (Brockelman et al 1998).
Maintaining a heterosexual, monogamous relationship is certainly advantageous at certain times, in certain contexts. But it is not universally adaptive, even within humans. Without anyone studying these behaviors in populations that use different reproductive strategies, and in the absence of comparative data to support these assertions, we are at an impasse.
Conclusion
In the words of a friend, EP is plugged into evolutionary theory with little more than a ratty old extension cord. EP takes some very basic, ancestral conditions, like differential costs of reproduction, and uses it in a sufficiently vague way that any behavior can relate to females generally being the ones to put in all the time and effort into making babies. Yet EP often ignores the three conditions necessary for natural selection, the mechanism for evolution. For natural selection to act on a trait, the trait must be variable, heritable, and produce differential reproductive success. Rarely does EP understand variation in a trait, rarely does it examine whether said trait has a genetic component, and rarely does it test whether their trait confers a reproductive advantage.
Are fertile women a threat to partnered harmony, their scents providing a temptation that noble men must suppress? I can’t rule it out, but I also think it is one of the least likely of many possible explanations.
Unfortunately for readers of the New York Times, Tierney loved this idea more than he loved interrogating it.
Acknowledgements
I’d like to thank Charles Roseman, friend, faculty curmudgeon and Bastard Colleague from Hell, for taking a look at an early draft of this post and providing commentary crucial to its improvement. Any rhetorical or scientific errors are my own.
References
Brockelman, W., Reichard, U., Treesucon, U., & Raemaekers, J. (1998). Dispersal, pair formation and social structure in gibbons ( Hylobates lar ) Behavioral Ecology and Sociobiology, 42 (5), 329-339 DOI:10.1007/s002650050445
MANER, J., GAILLIOT, M., & MILLER, S. (2009). The implicit cognition of relationship maintenance: Inattention to attractive alternatives Journal of Experimental Social Psychology, 45 (1), 174-179 DOI:10.1016/j.jesp.2008.08.002
Miller, S, & Maner, J (2010). Evolution and relationship maintenance: Fertility cues lead committed men to devalue relationship alternatives Journal of Experimental Social Psychology, 46, 1081-1084
Murdock, G., & White, D. (1969). Standard Cross-Cultural Sample Ethnology, 8 (4) DOI: 10.2307/3772907
