On Saturday, I gave a talk to the Minnesota Atheists on a bit of the evidence for evolutionary history. In one part of the talk, I gave an analogy for what biologists do, and I thought I'd expand on it a little bit here.

A theory is a powerful thing, a tool for interpreting observations and experiments, and the way to assess the utility of a theory is to examine how well it explains the available facts, whether it suggests new experiments and leads to new insights, and whether it contradicts any of the evidence. What we do with a theory like evolution is use it to interpret and assemble what we see into a coherent whole. The process is like assembling a jigsaw puzzle.

This, for instance, would be a single datum; an observation, like the discovery of a fossil hominid, or an experiment, such as a genetic perturbation of a Hox gene. It's the building block of our work. On a day to day basis, what scientists do is gather these little pieces of the puzzle; to a point, this can be done without any reference to a unifying theory. In isolation, they are often cryptic and esoteric, and honestly, the lay public has reason to be baffled about why we poke around with such odd things. Certain creationists of limited imagination, like Phil Skell, try to argue that the fact that a scientist can run a gel or dig up a bone without giving evolution a thought means that evolution is superfluous.

Think about what you do with a single puzzle piece, though: the next step is to go looking for a second piece, one that fits with it. In a typical jigsaw puzzle, you make inferences that you test. For instance, you may assume that it's a landscape, so blue pieces will be part of the sky, green pieces might be part of the trees or grass, etc., and we test those hypotheses by searching for pieces that correspond in color or texture to our first. The final test, of course, is to see whether two pieces actually fit together.

We repeat this process over and over. After a fair amount of progress, you usually have a general idea of what you're putting together. The way everything fits together, the general rules we see working (such as pieces that fit together well, and that we see sensible patterns emerging as assembly progresses) represent the theory. If none of the pieces fit, we'd have to announce that our theory of the jigsaw-puzzleness of the pieces was false. If there was no similarity in the texture or color of adjacent pieces, we say the theory of landscapeness was false. If we get to the point where our puzzle looks like this…

…we'd feel very comfortable with the idea that these assorted strangely shaped pieces of cardboard were part of a puzzle, and that once they are put together we'll have a photograph of some part of the world. It's nowhere near complete, but the big picture is coming into focus nicely. We keep plugging away at it, and we continue to make progress, so the theory is satisfying and unchallenged.

Of course, this analogy isn't perfect. We'd need a much more complicated puzzle, one that my daughter would balk at putting together, and it would also have to be unbounded. Evolution is one of the biggest, most complex puzzles humanity has ever faced.

Where do creationists come into this story? They're kibitzers. They're the annoying people who stand around and claim that there's no way this puzzle can be finished. Who reach in and pluck out random pieces and try to hammer them together. Who ignore the completed work and point to the gaps and tell you what goes there (and it has nothing at all to do with the developing theme of the image). They are unproductive nuisances.

Intelligent Design creationists are particularly aggravating. They pick up isolated pieces and declare that it doesn't fit anywhere in the puzzle—that it is anomalous and doesn't relate to any other piece. The scientist's response, of course, is to snatch it back and rummage around and find another piece with which it interlocks, but that doesn't stop the IDist. He just picks up another piece and repeats his assertion. They don't bother to explain where they think their purportedly anomalous piece belongs, either…it's enough that they declare without cause that it doesn't belong.

Without the theory to tie disparate pieces together, this is all we have:

That's biology without the theory of evolution: the facts are all there, but they are fractured and disorganized. We reject that, not just because it is esthetically unsatisfactory, but because it requires that we consciously neglect unambiguous connections—it demands a willful blindness. That's a trait common in creationists, but it is the antithesis of scientific thinking, where insight and the ability to find connections are valued.

(Thanks to Skatje for the puzzle construction!)