Population Variance

Trying to put down why I think other animals are not as cultural as humans, I think it's important to go off on a little tangent about the importance of variation in traits within populations... It'll take me a little while to get to stuff I consider less appreciated (and therefore more interesting), so please bear with me.

Darwin formulated his theory of evolution while ignorant of genetics. Rather than the atomic inheritance model developed by Mendel and others, Darwin believed in blending inheritance - offspring would tend to be about halfway between each of their parents in any trait. I know R. A. Fisher pointed out that it is very difficult to reconcile blending inheritance with evolution (though I don't believe he was the first to make the point), because blending inheritance naturally reduces the variance of a trait in a population from generation to generation. In fact, I believe variance is supposed to be halved in each generation, when each child is thought to be the mathematical average of the parents. The existence of wide variation in nature, when coupled with blending inheritance, implied an impossible amount of adaptively more-or-less neutral mutation.

Hardy and Weinberg showed that this is not the case for Mendelian inheritance - for each generation reproducing by mixture of atomic genes, in a large enough population, with no selective advantage between genetic variants, and with a couple of other constraints, there will be no change in population variance in genes, or in the traits expressed by these genes. This equilibrium is actually a pretty strong force in a large number of species - in other words, the current gene pool has a lot of inertia, and evolutionary forces will generally act very slowly.

Let's take an example: Peter and Rosemary Grant were able to observe evolution occurring in Darwin's finches through two severe ecological changes - in one case, a drought, and in the other, a flood - and watched the distribution of beak sizes in the population change in response to both events - in the one case, the beaks became shorter and wider to crack open the tougher seeds during the drought, and then longer and narrower after the flood to more efficiently access the softer, smaller seeds that then became abundant. To give a sense of what may be happening evolutionarily, I'll construct a deliberately simplistic genetic model of beak shape: say there are four genes, each with two alleles, that determine the beak shape of a finch. For each gene, one of the alleles will cause the beak to be more stout, and the other will cause the beak to be more lean. We'll call the "stout" allele 0, and the "lean" allele 1, and overall beak shape is determined by how many "stout" and (by definition) "lean" alleles the organism possesses. Any individual in this population will then have K stout alleles, and 4-K lean alleles.

I've set this up to deliberately produce a binomial distribution of beak shapes (though there are complications even here - I note these complications in order to ignore them). In our model, we'll say that after the drought individuals with 3 stout alleles and 1 lean allele will have the optimal beak shape; after the flood, individuals with 3 lean alleles and 1 stout allele will have optimal beak morphology. In neither case should any allele be completely eliminated from the population, which means that there will always be the potential to adapt to the flood after a drought, and to the drought after the flood.

This leads directly to what I think is the core of why culture is not nearly so intensely used in non-human animals as it is in humans: cultural evolution includes a lot of blending of received information, blending inheritance reduces population variance, and reduced variance lowers the ability to respond to ecological change. I may unpack this more later...

Evolution of institutions

One of the themes from the post on religion below is that institutions can profitably be regarded as evolved entities in their own right. This echoes group selection theory, but I don't really intend it that way. An evolutionary theory to account for modern human behavior needs to include the concept that individual humans are (or can be) members of several communities at once, which may have conflicting hierarchies. It is not clear to me that the usual formulations of group selection consider humans in this way. Besides which, the success of an institution is not necessarily linked to its ability to create copies of itself - often, stability over a long time period is intuitively a better measure of an institution's success. The generally declining marginal contribution of additional group members to group success (which is an assumption frequently made in economics to describe why firms eventually stop growing or shrinking) suggests that group selection theory must ultimately favor the creation of new groups. This is not necessarily true of institutions.

Institutions, to me, can be described more or less as basins of attraction. I say this with some reservation, because I'm not well enough versed in the mathematics to be precise. I understand a basin of attraction as a concept in dynamical systems, used to describe more-or-less regular trajectories through the space under consideration. For example, the trajectory of astronomical bodies (planets, stars, etc.) are well described by differential equations - astral body acceleration at any instant depends on the body's position and mass, and the position and mass of any other astral bodies nearby. Without getting too deep into it, this dependence of acceleration on the positions of several mobile bodies makes modeling the motion of the planets actually quite a bit more complex than one might naïvely expect (see the N-body problem for details). The orbits of the planets within the solar system are regular to the extent that they are caught within the solar system's basin of attraction. (I'm happy to be corrected on this.) Incidentally, "adaptive peaks" on Sewall Wright's "fitness landscape" are themselves essentially basins of attraction... As are other evolutionary scenarios, such as rock-paper-scissors games described by Maynard-Smith (in which an individual is committed to a strategy at birth - in this case, there is no ESS. nevertheless, the path through time is quite regular: scissors is replaced by rock is replaced by paper is replaced by scissors. I've wondered if this scenario perhaps accounts for nuptial-gift patterns in insects, which I may expand on later).

This sounds excessively complicated, it probably is excessively complicated. But that doesn't mean that this sort of thinking isn't useful. Ecology in general is considered by those who study it as a very complicated dynamic system. Adaptation is considered to follow a trajectory on a fitness landscape defined by the entities in the ecosphere, which is a very complicated beast. Studies of biological adaptation, however, greatly simplify this picture by considering a denuded subset of the ecosphere, and model but a few variables of interest.

What I am trying to get at can be expressed much more simply: a successful institution will select for (that is, recruit and/or develop) the individual or individuals best suited to carry out a role in that institution. The method of selection is a property of the institution, and of the available "talent pool", and will also reflect interactions with other institutions in the cultural web. Understanding the evolution of institutions is a question of how these institutions' mechanisms for selecting or cultivating new individuals in different roles change over time, and understanding the adaptations of institutions will mean describing the circumstances under which different forms of selection or cultivation tend to be more or less successful.

It's probably hubris, but I suspect that research following such a program would do better describing behavior on a global scale than any approach which treats institutions as mere epiphenomena.

I hope to unpack some of this discussion later.