Wednesday, January 16, 2008


Hey, that was a pretty clever title, wasn't it? I bet I'm only the twenty-four thousand, two hundred and sixty-eighth person to come up with it and use it to title a blog post.

Anyway: let's talk about evolution, okay? We need to have a chat.

I've been noticing a few things in common parlance which, as an ad hoc evolutionary biologist, make me cringe. The first is group selection, which was supposed to have been done away with by no less than Darwin himself, not to mention countless successors, but still somehow persists in the popular lexicon. What am I talking about? Well, let me explain it with a little bit more clarity. I don't ever want to hear any one of you say again, ever, any of the following things:

"For the good of the species"
"Survival of the species"
"Groups that had [trait] survived better"

...unless you're being very specific and advancing some fairly complex evolutionary biological ideas. Let's just go ahead and get this straight, on the (surely small!) chance that you haven't followed that link to my senior thesis and committed it all to memory: the unit of natural selection is the individual; more specifically, the benefit is always, always to the ability of the individual to pass on its genes. It is not, now or ever, under any circumstances, the group. (There are apparent exceptions to this rule, such as eusocial insects [Hymenopterans, e.g. ants, and bees] and certain populations of things such as elephants which appear to be group selected, but it just doesn't hold up under scrutiny. We can discuss this more later.) When a trait is beneficial, it is beneficial to the individual and makes the individual more likely to survive. When it is also beneficial to a larger group, it is, without fail, because that is beneficial to the individual. Monkeys groom one another because it allows them to get themselves groomed. Bees sacrifice their own reproduction because it furthers the reproduction of the queen, with whom they share on average 75% of their genes. (For this last, it is important to note that genes are just information, which makes no distinction between which copy of a gene is passed on. Effectively, all copies of a gene are the same.)

The short of it is, natural selection always selects on the individual, because it is the individual who lives or dies. Kin groups have closely allied genomes, which means that it benefits an individuals genes, in certain cases, to care for kin, and even the whole species. See Richard Dawkins' The Selfish Gene for an excellent work on this topic, perhaps even the pre-eminent work. Don't worry; it's good science, from before he turned into an evangelical atheist. I don't have time or space to explain the whole concept here, but suffice it to say that genes are, in fact, selfish, and always act to benefit their own continuation and that of the individual who carries them.

Okay, next!

Not everything is selected. By this I mean the following: life is a complicated thing, and many epiphenomena emerge from the crucible of natural selection which are not, themselves, directly selected for. Everything is evolved, but not everything has a direct purpose.

This one comes into play a lot in behavior. People see an animal (yes, often humans) act a certain way, and so they create a weird hypothesis about why that behavior evolved. Sometimes, they're right; sometimes, they're wrong, and it evolved for a different reason. Sometimes, though, it just happened as an accidental side-effect of other behaviors which were beneficial. This seems to be the case, for example, for many of people's learned behaviors which don't provide any apparent survival benefit. The ability to learn complex things was greatly beneficial; what we learn seems to just happen.

The message here is this, I guess: if you see a trait of life, feel free to create hypotheses about why it is how it is, but include among those hypotheses the idea that maybe it arose as a side-effect of something else, perhaps something entirely unrelated to your previous line of thinking.

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