Saturday, June 25, 2011

Love, Sex, Babies, and Neural Correlates

A possible solution to the mystery of why postpartum disfigurement has persisted as a trait detrimental to sexual desirability, despite correlating with fertility, is this: once human pair bonding has occurred, visual assessment of attractiveness of one's partner (or other members of a partner's sex) ceases to be an important motivator.

What would really nail this theory home, for me, is if fMRI studies demonstrated some kind of reduction in processing the physical sexual attractiveness of one's partner and others during the postpartum, pair-bonded state.

Analogously, analysis of what we polys term "New Relationship Energy," which mortals call "being in love," indicates that this phenomenon is associated with deactivation of neural areas associated with critical social judgment of others. Once the "decision" to be in love has been made (by your body, not by "you"), the brain ceases evaluation of the love object in social terms. (See, e.g., Andreas Bartels and Semir Zeki, "The neural correlates of maternal and romantic love." NeuroImage 21 (2004) 1155–1166.)

This is what Héloïse d’Argenteuil is making concrete in what is still the most righteous expression of romantic love I have yet encountered, from her first letter:
God is my witness that if Augustus, emperor of the whole world, thought fit to honor me with marriage and conferred all the earth on me for ever it would be sweeter and more honorable to me to be, not his empress, but your whore.

Its elevation above the self-interested social congress of the world is at the heart of the righteousness of romantic love.

I refer to this only by analogy. NRE is not at all the same phenomenon as the postpartum pair-bonded state that I have in mind. The early stage of love, as we polys remind ourselves with our terminology, lasts no longer than a year, maybe two, if you're lucky. (See, e.g., Enzo Emanuele et al, "Raised plasma nerve growth factor levels associated with early-stage romantic love." Psychoneuroendocrinology Vol. 31 Issue 3 (2006) 288-294.) The state of mind that must support monogamous love and continued investment despite postpartum disfigurement occurs after, and lasts much longer.

I don't imagine a woman who has gestated a baby would be eager to see the brain scan of her lover while he looks at her naked body. Nonetheless, it's hard to deny that this is important information for people considering whether to have a baby.

6 comments:

  1. Such an fMRI study should include female-female couples. There are (close to) natural controls out there in the form of homosexual relationships that get underutilized in this area of science. And, of course, homosexual relationships are worth studying in and of themselves.

    Also, with regard to how long the "early stages of love" last, the Emanuele study reports summary statistics that reach consistently into the first moment, inconsistently into the second moment, and never into the third or higher moments. Anecdotal evidence from my own relationships and those of intimate friends suggests that there may be a pretty wide spread, or if not a large second moment, a lot of rightward skew. To be fair, a share of the relationships contributing to the rightward skew are relationships that had a long-distance phase relatively early in their history. Also, relationships where the initial energy fizzles quickly often don't have enough time to establish themselves, and thus would get excluded from the study.

    (For the sake of any who happen not to be conversant with these statistical terms, "second moment" basically means "standard deviation", or how spread out the data is. "Skew", the third moment, means the extent to which the data has bigger tails in one direction rather than the other.)

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  2. JasonSL, I know what statisticians mean by 'moments', but your use of them is non-standard. How can summary statistics reach into moments?

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  3. neq1,

    My understanding, not as a statistician but as a biophysicist, is that "summary statistics" are statistics used to summarize a distribution. They typically include some measure of central tendency, most commonly the mean, and some measure of dispersion, most commonly the standard deviation or variance. The mean of the data is the first moment; the variance is the second moment (about the mean).

    The third moment about the mean is the skew, which is a measure of the asymmetry of the data, and the fourth moment about the mean is the kurtosis, which is a measure of how "pointy" the data is. Distributions with high kurtosis are pointy in the center and have relatively fat tails, which means that dispersion in the data comes relatively more from a few outlying data points than from a larger number of closer-in data points.

    So if you report the mean and the standard deviation of your data as the only statistics, then your summary statistics include the first and second moments of the data but do not "reach into" higher moments. I think my use of the terms is pretty standard.

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    * The "conventional" moments are the ones discussed here. There are other definitions of the moments in, for example, L-statistics. The second L-moment is not the variance but rather the mean absolute deviation. So qualitatively speaking, second moments relate to dispersion, third moments relate to asymmetry, and fourth moments relate to the extent to which the dispersion owes to a large number of points close to the center or to a small number of points far from the center.

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  4. "the mystery of why postpartum disfigurement has persisted as a trait detrimental to sexual desirability"

    Natural selection can't do everything. The slogan is that evolution is a satisficer, not an optimizer.

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  5. JasonSL,

    Now I understand. You're just saying that they usually didn't report statistics that summarize higher order moments.

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  6. neq1,

    Yup, and that getting the story right might depend on the entire distribution of the data, which higher-order moments would help describe.


    Mitchell,

    Well, maybe it *can* do any given thing, but there are tons of things that it doesn't get around to.

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