You focus, Steve, on what is still the most baffling question for me in all of psychology: How do we learn from the environment? Why in some cases does learning catch like a wildfire, but in other cases why do the sparks just fall on wet kindling and snuff out? Why is the environment so potent in some cases and in other cases so anemic?
I started my professional life in the 1960s as a learning theorist in the hope of finding out. I soon hit my head against four problems, each of which told me that all the usual explanations failed. The first was learned helplessness, and the problem was how could we learn so easily about the two simultaneous conditional probabilities that make up noncontingency when associations are only about simple pairings? The second was the functional autonomy of motives, and the problem was how do some acquired motivations, like fetishes and phobias, come to have such enormous strength after only minimal experience? The third was taste aversions, and the problem was by what mechanism is taste-illness learned so easily, but taste-shock not learned at all? The fourth was the problem you have wrestled with so well: How is something as complex as language so easily and universally acquired by children?
To this day, not only are these problems unsolved, but also new ones have arisen: the Flynn effect (why has the average IQ risen by 15 points over two generations in every rich country?), the insignificance of shared environment (why are adopted sibs so very different from their non-adopted sibs even though they are reared the same way?), and the irrelevance of childhood experience to adult personality (why in twin studies does adult depression have so little to do with childhood misfortunes?). I suspect that these are all pieces of the same puzzle.
But to say that these are "prepared," "evolutionarily predisposed," "contra-prepared," "tipping points," "catastrophic," "kindling," "chance," or "modular," does not give us a mechanism, it only renames our ignorance. Psychology is desperately in need of a new "learning theory" that takes genetics seriously.
Authentic Happiness hints at one solution: unfolding versus flourishing. Much of the stuff that is heritable (e.g., anxiety, language, taste-aversion, prejudice) is tied to survival selection. It makes sense that the zero-sum-game of life or death should depend on relatively unmodifiable mechanisms that unfold across life and are triggered by stereotyped threats. These make up the underside of living, the foci of negative emotion. Flourishing, if Bob Wright and I are correct, is, in contrast, about positive-sum-games, growing new structures ("Look, I made a hat where there never was a hat before"). Human happiness, not usually measured in twin studies and as yet untested by the nurture assumption, may be much more buildable by parents, by culture, and by mentors. Our parenting works, not because of a shared negative environment (we watched the awful events of 9/11 on CNN together), but because of an unshared positive parenting environment (Nikki does ballet, Darryl does karate, and Lara writes). That which makes life worth living—positive emotion, strength, talent, purpose, and virtue—may be just the place where the environment works and where the blanker slate reigns.
So, with this confession of ignorance, our conversation on Slate ends. I would not have it finish, however, without a point of personal privilege. The Cambridge mathematician G.H. Hardy said that when he was with tedious people he would console himself by thinking, "At least I was at one time able to collaborate with Ramanujan at almost his level." The same goes for me: I think I will always take pride in imagining that for a few brief days I was able to converse with Steve Pinker and Bob Wright at almost their level.