In Practice: Madonna-Whore: Not Complex

By Peter D. Kramer in In Practice :

If you want to pass on your genes, you might hold out for a quality mate and raise your offspring with care. On the other hand, you might just enjoy promiscuous sex and let the pups fend for themselves.

What determines which strategy you’ll choose? Your mother — or rather, the early life experience she provides. That, and how your genes fold. At least it’s that way for rodents.

At the annual meeting of the American Psychiatric Association, Michael Meany, a psychobiologist at McGill, presented the results of years of work on mothering, genes, and behavior in rats.
If a rat mother is nurturant (she tends to lick and groom her pups, making her “high LG”), her offspring will be less anxious, better at facing stress, and good at parenting their own broods. Low LG mothers produce does who encounter puberty early, show greater sexual receptivity, enjoy an increased pregnancy rate, and neglect their young. Subsequent generations of female offspring will do the same — unless a lucky pup is “cross-nurtured” by a mother who licks and grooms, in which case the cosseted rat will grow up to be be calm and picky.

These responses typify two Darwinian strategies. If the early message is that life is

nasty, you pass your genes on any which way. If you begin with a quality environment, you choose a more patient strategy.

The personality variants result from the way the brain handles the usual suspects: stress-responsive hormones, serotonin, and oxytocin. But in Meany’s rat model, at the base of the difference is an extremely simple difference in epigenetics.

Remember epigenetics? It refers to changes in the configuration of chromosomes that maintain the same gene sequences. Here, neglectful rearing results in the methylation of single base, a cytosine, found in a “non-coding” region of DNA that turns out to influence the production of receptors for stress hormones, via a “glucocorticoid receptor promoter.” It's not your genes, it's how they're folded, a geometry that encodes the trouble you've seen.

A “histone deacetylase (HDAC) inhibitor” that helps reverse the methylation and refold the gene will make the low-LG offspring more resilient in face of stress. Absent this chemical re-parenting, once the methylation occurs — as it invariably does in the offspring of low LG mothers — it persists for a lifetime, muting the production of stress modulators even in flush intervals. The pattern will continue for generations, in a sort of rat family “culture of poverty.”

In human terms, if you, as a woman, get knocked up young and neglect your child in favor of more hot hookups, it may be a single methylated cytosine that’s to blame — or to praise, if that strategy works for you and yours. And if, as a man on the prowl, you think that the complaisant babe you’re ogling learned life’s lessons in the school of hard knocks, you’re probably right.

For more detail, you can download the first paper listed in this bibliography of Michael Meany's work. The essay concludes: “The quality of the environment influences the behavior of the parent, which in turn is the critical factor in determining whether development proceeds along an optimistic versus a pessimistic pattern of development. In mammals, . . . parental signals serve as a ‘forecast’ of the level of adversity that lies ahead. . . . various levels of environmental demand require different traits in the offspring. This is a simple, even obvious message, with significant social implications.” It’s also one that may be encoded reasonably simply in the mammalian brain, via DNA that’s responded to the way of the world.

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