Group vs Individual Selection in Evolution

Last June’s Edge had an interesting essay by Harvard professor Steven Pinker on why the idea of group selection as an extension of natural selection is wrong. His position is to take the baseline definition of evolution by natural selection

The core of natural selection is that when replicators arise and make copies of themselves, (1) their numbers will tend, under ideal conditions, to increase exponentially; (2) they will necessarily compete for finite resources; (3) some will undergo random copying errors (“random” in the sense that they do not anticipate their effects in the current environment); and (4) whichever copying errors happen to increase the rate of replication will accumulate in a lineage and predominate in the population. After many generations of replication, the replicators will show the appearance of design for effective replication, while in reality they have just accumulated the copying errors that had successful replication as their effect.

rewrite this in terms of groups

Natural selection could legitimately apply to groups if they met certain conditions: the groups made copies of themselves by budding or fissioning, the descendant groups faithfully reproduced traits of the parent group (which cannot be reduced to the traits of their individual members), except for mutations that were blind to their costs and benefits to the group; and groups competed with one another for representation in a meta-population of groups.

and show that this is not what is going on (and everyone agrees that it’s not what’s going on) when people talk about group selection

In every case I’ve seen, the three components that make natural selection so indispensable are absent.
(a) The criterion of success is not the number of copies in a finite population (in this case, the meta-population of groups), but some analogue of success like size, influence, wealth, power, longevity, territory, or preeminence….
(b) The mutations are not random. …innovators use their highly nonrandom brains to figure out tactics and institutions and norms and beliefs that are intelligently designed in response to a felt need (for example, to get their group to predominate over their rivals).
(c) The “success” applies to the entity itself, not to an entity at the end of a chain of descendants. It was the Roman Empire that took over most of the ancient world, not a group that splintered off…
On top of these differences, most of the groupwide traits that group selectionists try to explain are cultural rather than genetic.

There are really two different questions here. First, does group selection work in biology? Can a herd of fleet deer be selected for as a fleet herd of deer? Second, can the group selection concept be applied at a societal level? Can group selection tell us something about the Roman Empire? Herewith are some of my (unresearched) thoughts on the questions.

BIOLOGY
What makes evolution difficult to discuss at a meta-level is the fact that the causes and the effects are so widely separated and so conceptually distinct. Evolution acts at the DNA level, but that’s not what it acts on. DNA is a component of genes, and genes produce proteins (DNA also controls how those proteins are expressed, but let’s keep this simple). These proteins change the phenotype of the individual, promoting physical changes in bones that allow an ape-descendent to bang the rocks together, or in the brains that make the ape-descendent wonder what happens if you do.

DNA->gene->protein->individual fitness

So, horses with harder teeth can eat the new grasses and thereby survive and reproduce, but it’s changes in the DNA that is part of the genes for tooth enamel that gives them those hardened teeth.

So, the question is, is there some way that we can add one more step to the chain? Is there some way to conceptualize
DNA->gene->protein->individual->group-fitness

I’d say that any connection is tenuous, but I think you can make a limited case. Take a herd animal. We know you can reproduce flocking/herd behavior with three simple rules (do the wiki on ‘boids‘). The thing about the flocking rules is that they only work in a flock. They are expressed in the individual, but work at the group level. It’s not that you have a herd of fleet deer, or a fleet herd of deer, it’s that you have a herd of deer at all. This is similar to the ‘Baldwin Effect’ where, if evolution has caused you to choose a lifestyle that involves living in herds, the kinds of modifications you will see will involve ones that better prepare you for herd life. In systems terms, you might call flocking behavior an emergent feature of a group, and the conceptual problem is, how do you tie an emergent feature back to the DNA of the individuals in the group.

SOCIOLOGY
The process breaks down when we try to carry it further and talk about societies as evolutionary subjects. At least, it breaks down in technical terms. As Pinker points out, societies don’t reproduce by DNA replication, and the successful societies aren’t distinct entities from their predecessors, but just their predecessors at a later point in time. It was the Roman Empire that was successful, not some mutated clone. This is all true, but it misses the point.

One of the most powerful tools in thinking about nature is the use of metaphor. There is no such thing as “the number line” in nature, but mathematicians become good mathematicians by being able to manipulate that and other mathematical metaphors. Richard Dawkins himself (and he has a comment supportive of Pinker in the essay) coined the term meme as “an idea, behavior or style that spreads from person to person within a culture.” What’s happening here is that the meme is used as a metaphoric gene to let us think in different ways about tough ideas.

Now, memes have many of the characteristics of genes (think about how ideas spread, and compare that with the list at the top of this article), and the sociotypical result emerging from a large collection of memes is what we call a society…metaphorically. To the extent that this metaphor helps sociologists think about a complex topic, I’m all in favor of it. And to the extent that such a memotype->sociotype metaphor captures some emergent property of a society, there is room for a Baldwin Effect and group selection.

The key requirement is this, that this use of metaphor as a tool must throw up testable hypotheses. If sociologists can’t do that, then they fall into the same camp as the post-modernists in literature, as people who have pushed a useful tool (deconstruction) too far and ended up in nonsense land.

UPDATE 2014: Here’s E.O.Wilson, mentioning group selection in a discussion of alien life.

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One Response to “Group vs Individual Selection in Evolution”

  1. Kurt Kremer Says:

    Thanks for responding to Pinker’s piece–I read it recently but haven’t had time to think clearly enough about it to discuss it outside of the dusty corners of my brain. As much as anything, it seemed like Pinker was stressing that absolute models/ephiphanies don’t work absolutely when applied to life. Group behavior is both a response to environmental forces and an influence, at least for social animals. Sociology (used to, at least) fall into two main camps–group behavior (driven by stats) and individual behaviors–driven by story. We’re not ants or bees (and maybe they aren’t, either). But we are influenced by the approval, security, and richer possibilities that comes with groups. We’re also overloaded as individuals by group behavior (the Web being our current extreme)–where extreme and mundane behaviors are rewarded (I wonder if this is similar to what happened when we ventured out of the trees and into the plains…) Okay, I didn’t mean to turn this into a rough start to my response. More anon from my own podium later. Again, thanks.

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