Monday, October 10, 2011

The Truth About Evolution

It might not be quite the same in other places, but in Australia - anecdotally - it seems like the level of scientific literacy is high enough that the vast majority of young people say they believe in evolution. The problem is, many of them profess belief, and maybe have a vague idea of how it works - but don’t actually understand it well enough to apply it properly in arguments.

This is why you get people attributing powers to evolution that it doesn’t have. You get people who insist that they don’t want medical staff anywhere near them when they give birth because it’s “natural”. You get people who argue points based on what nature “intended” us to do. Basically, you get a lot of people who label it evolution but talk about it like Intelligent Design.

I didn’t do a lot of biology in high school, so I don’t know how well evolution is taught there - and in any case, if you really want to understand evolution you should probably read a book instead of a blog post. But it seems like most people get their ideas about evolution from pop culture, so I want to try to clear up people’s perception of it.

The first thing you need to know about evolution is that it’s inherently reactionary. The process of natural selection goes like this: there is a random mutation. If it’s a really bad one, it’ll kill the organism and it won’t be passed on to the next generation. If it’s a good or fairly neutral one, or if it’s bad but the organism can compensate long enough to reproduce, it will get passed on. If it is really good - and things are deemed “good” only with respect to how well they allow that specific organism in that specific environment to live until it reproduces - it will eventually become common, through the purely statistical fact that organisms with that mutation are more likely to survive and reproduce than those without it.

That’s it. There is no evolution fairy that sits there and says “Hey, I know it’s not much good now, but that gene has a lot of potential! I’d better hang onto it for later.” There is no foresight, there is no intent. It’s the simple maths of what works in the here and now. It can’t plan ahead; it only reacts to what worked last time. Sure - things that were once useful stick around past their use-by date, and occasionally those things get used for a different purpose. For example, land-specific limbs get repurposed as flippers on dolphins, feathers that were used to regulate body temperature get used to help birds fly, etc. But all of that is just accident; evolution is not some process of gradual improvement or refinement. It’s a series of accidents, with the least-shitty examples being perpetuated.

This game really illustrates the point well. It uses evolutionary algorithms to build cars; the longer the randomly-generated design goes without grinding to a halt, the more likely its template will be incorporated with the next generation (the attributes of the cars are blended between rounds to simulate breeding). So a car that goes a long way will be better-represented in the next generation than a car that crashes early, and so on until you breed in good adaptations and breed out bad ones. But try this - sit there for five minutes, cheering on certain designs because you, as an intelligent observer, can see that they have potential. Watch as, over and over, a design that would be by far the best - if it weren’t for one tiny flaw - gets out-competed by cars that are competent now but won’t ever be fantastic. After five minutes of that you will understand just how slap-bang and capricious evolution really is.

People often talk about natural selection in awed tones, saying what remarkable products it has wrought. And sure - I’m down with that. It is fascinating, and given that we arose from completely random processes we are pretty marvellous - and the last thing I want to do is to make nihilism seem like the logical progression from evolution. But at the same time it’s important to be realistic about it.

Because the second thing is, evolution is ongoing; we are still evolving. And it pays to remember that the mechanism by which evolution works is by killing what doesn’t work - so every creature that failed nature’s test was just as much of a remarkable product of evolution as we are. We are not immune from this process, by any means, so what nature provides us is absolutely not guaranteed to be enough.

A particularly good illustration of this is cancer. Cancer is basically as evolutionarily fit as you can get - cancer cells contain mutations that allow them to reproduce much more quickly than normal cells, and have figured out how to reroute resources from your body to do so. They are so fit, in fact, that they eventually completely take over their host body and kill it. This is how evolution works - it can’t see ahead to say “Woah, that rate of growth is unsustainable, we’d better put the kybosh on that!” All evolution sees is that it’s working now, and it does not care in the slightest if it eventually kills you.

Evolution gave us the eye. But it gave us an eye with an optic nerve poking through the retina at the worst possible spot, giving us a blind spot right in the centre of our field of vision. It gave us the ability to walk upright and use our hands more freely…but at the expense of knees that are poorly suited to our posture, a spine that wasn’t really built for it either, and a change in our pelvises that makes childbirth much more hazardous than it was before (the text of that article is the important bit, but beware that there are videos of births at the bottom). It gave us a useless appendix that is prone to inflammation, it gave us a jaw too small for our teeth, it gave us reproductive organs that don’t work properly inside the body and so have to hang out the front in a sack.

We are not efficient, perfectly-designed machines. We are the epitome of “near enough is good enough” - the product of a few billion years of being just good enough to scrape by…for now. Remember this next time you talk about what nature intended.

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