Sunday, June 12, 2005

Post Hoc Ergo Propter Hoc

Big D. replies:
I encourage my readers to look at this trackback. Once you wade through the huff and the puff, you’ll see that Rosenau’s main point is the second option I consider. As for his remark that we do medical experiments with mammals (i.e., “Why test in mammals? Because humans are mammals. Understanding common descent helps us avoid poisons and ineffective medical treatments. “), this is properly a structuralist argument and works more naturally from a common design vantage. By the way, Paul Lewis developed an effective vaccine against polio in 1908 for monkeys but it took another 50 to develop one for humans. How much did evolution help here? –WmAD
Bzzt, wrong. The fact that he misunderstands is a separate problem. He presented two options, one in which humans mimic evolution, the other in which we strive to counter evolution as it happens. I offered several more options, which he chose to ignore. Then he deleted a trackback comment pointing that out. Ah, gotta love that free and open exchange of ideas.

I offered a third and very different option than his original two. By understanding the process of evolution, we can engage in policies which let us minimize evolution in bacteria and in insect pests. The latter is called Integrated Pest Management, and is a big deal in agricultural circles.

The fact that common descent is useful is yet a fourth option, one he failed to consider, and one which does not derive from "common design." I'm not sure what his claim is about structuralism, and the wikipedia doesn't help. Maybe someone can tell me if he's inventing new usages or if there's a meaning to this usage.

The problem with design is that we can't move past someone shouting "common design." Why did the designer choose to make all mammals with certain biochemical pathways in common, and why are there bizarre and niggling differences? Polio has a different physiological response in chimpanzees, and at least one vaccine worked in people but not in chimps. Weird shit happens, but that makes less sense if you have a designer than if you have random variation and selection.

If I were a petty jerk, I'd title this "Got a problem explaining away evolution? - invoke common design" because that's all that line about common design offers. Why should a common designer make all mammals similar in their response to various drugs, microbes, etc.? Who knows! To answer that, someone would have to say something meaningful about the designer.

Let's expand the point. Why not design a perfect physiological human analog that lacks a soul/consciousness/whatever? Wouldn't that be more compelling than the existence of total eclipses (the evidence offered in Privileged Planet)?

Oh, but to answer such questions requires specifying the Designer and nailing down something about it and its desires, so never mind.

But let's back up. Why is it bad to say that we use the results of evolution? Dembski claims that these two statements are the same:
  • I use models of biological evolution to design better drugs.
  • I use the products of evolution to discover better drugs.
Here's the difference. If I model evolution, one can argue that there is a teleology implied in that. They'd be wrong, but they could say it. At worst, it's a bad analogy to biological evolution, and arguments from analogy are always dubious.

If, instead, I find something useful, no such problem arises. A non-teleological process happens to make something useful. The fact that I use it does not retroactively create teleology or "design." Think of the beginning of 2001: A Space Odyssey. An ape gains intelligence from the monolith and uses a bone as a weapon. The bone wasn't designed as a weapon, but it can be put to that use. No teleology.

Dembski claims that the intelligent use of the products of evolution invalidates a claim against design. I say that design better offer more than explanations after the fact. The fact that we use something for a function afterward doesn't mean it was designed for that purpose.

Post hoc ergo propter hoc.

It's not clear how to distinguish between the two cases in practice. Did Buddha step in and change the fitness landscape to achieve some teleological aim, or did animals evolve according to a normal measure of fitness (eg. the probability of a genetic lineage passing on to the future). Post hoc, how can we determine that?

IDC usually implies something fancier than that. It usually implies that the designer actually designed a structure and made something that couldn't be made otherwise.

The trick to evolution is that the two approaches combine. A structure might begin for no clear reason. An odd change in a protein, a weird bump on a claw, a different jaw articulation, whatever. It turns out that the new protein shape isn't damaged by penicillin, and suddenly, that change has a "purpose." Post hoc we can see "design," although none existed beforehand.

What if it only offers some protection against the drug? The individuals with the mutation will survive longer, those without will die. Maybe there was some natural variation in a second gene beforehand. The first mutation occurred along with allele 1. After some recombination, it winds up alongside allele 2. Those two genes interact in a different way, offering better protection. Again, the individuals with allele 2 and the mutation survive longer. It looks like design, but it's not. After the fact, it looks like design, and the process of natural selection actually is imposing teleology. The mutation lacks purpose, but the selection is purposeful. The purpose is to survive and to make a population that doesn't go extinct.

The tricky thing is that that purpose emerges organically from the population, not extrinsically. The purpose emerges from the population and is what we call an "emergent property."

Thanks also to afarensis for the link to Darwinian Medicine, and to decorabilia for reminding me to point out the TalkOrigins answer, as well as providing his own answer.

Enough talk for now.