On the "Moral Instinct"
You only *think* Pinker sometimes annoys you, Amanda. Just try to imagine how an evolutionary biologist feels about his slapdash theorizing.
Looking at the list:
harm, fairness, community (or group loyalty), authority and purityfrom the POV of an Actual Evolutionary Biologist™, I find myself singing one of these things is not like the others. Harm, fairness, loyalty, & authority can all be described in ways that make sense for any social animal.
For instance, baboons (as in the book I recently reviewed) respect authority, in that they take careful account of status in their dominance hierarchy. Baboons also show loyalty, by forming matrilineal family alliances that rise or fall together.
But purity is different. It is not a moral principle that comes out of our natural social life, I don't see any continuity between "purity" and animal behavior. Tellingly, only situation #5 above involves people "acting like animals" -- because animals show no equivalent of this moral category alone, even though they can be fair, obedient, loyal, and reluctant to harm.
So I think the liberal moral philosophers & psychologists who don't include "purity" as a moral principle are not being arbitrary or capricious. Purity *isn't* a moral principle in the same way as the others are, it's a different category of thing.
I would imagine (at least some) animals do display a concern for “purity” in that sense by keeping their waste away from their food, yes?
Some do -- but the ones I know offhand who do are rodents (e.g. prairie dogs, but I've seen it in mice, too). Primates are natural slobs and humans haven't had permanent "nest sites" all that long by evolutionary standards, so no, I wouldn't expect "purity" to be "programmed into us" the way loyalty or compassion may be.
My biologist's spidey-sense suspects that "purity", as an obsession, may be a function of language and/or conceptualization -- that it's related to the way we create conceptual categories, "A not B". Not enough is yet known about animals' mental categories to say what the continuities are, but certainly it's not obvious in our closest relatives.
I should add that the reason many rodents are neat housekeepers is when they live all their lives in one set of tunnels or other restricted spaces, spend most of their time inside, and store food in their “houses”. Such rodents will have separate rooms for evacuation, for food storage, and for babies.
I once found that mice had been living in the back of my china cupboard, where they had very neatly been using the tea light holders for toilets, while they had filled the small vases with seeds. Freudian analysis of the mouse psyche would be fascinating.