Monday, July 7, 2008

The rock wall analogy

Imagine laying a natural rock wall without mortar. Good rock walls minimize the empty space between the rocks. Bad rock walls leave a lot of empty space and tend to fall apart.

To lay a rock wall, you start by setting some rock. Then you appreciate the empty space beside it. Then you look to your rock pile for something that will best fit that empty space. If you're slow and careful you will probably build a pretty good wall.

But imagine building not just a good wall but the best wall possible given the stones available. Could you accomplish this? I don't believe I could.

If you've ever constructed a rock wall, you've likely had the experience of discovering a spot that would be perfect for a rock you've already set. Ugh! Sometimes you'll unpack a little of the wall to get the rock for that space. But the unpacking sometimes creates new spaces that are hard to fill.

It's just too difficult predicting at the outset where each rock should ideally be placed.

Now, imagine you've got a large steel box in the shape of the wall you're building. The box sits on top of a platform that can be made to vibrate. Put all the rocks in your pile into the box and let the thing vibrate a while.

Q: Which wall will have less empty space in it, the human designed wall or the wall that results from vibration?

A: The vibration method will have a better outcome. Here's why:

1. Rocks that share large surface areas will vibrate less than other rocks, thanks to friction.

2. The variation in movement among the rocks allows for a kind of natural selection: rocks that don't move will "pass on" their stability to future rock arrangements while mobile rocks will continue to bounce until they find a snug spot.

Evolution is like an adding machine that can add together all sorts of interacting forces all at once. We find this process hard to understand. As humans, we can only add two numbers together at a time. So we look at evolution and we call it "random" because we can't see all the interacting links. But it isn't random. It's complex.


  1. That's one thing the creationists always overlook. Evolution is not about one mutation at a time, there are several in any given organism, and millions in a population - all interacting, all being selected on their own or in combinations. Then we have sex wich speeds up the mutation spreading process. These are things creationists leave out when saying that there is not enough time for evolution to have caused the diversity that we see.

  2. ok, setup your vibrating wall-maker experiment and let's see your data. science is science. doesn't matter who or what process created it. perhaps physical shaking will move stones, but what kind of sub-molecular shaking causes mutation. Also, to what are you comparing the empty space between the stones? What will happen when you remove the steel box? Hand-laid stones are purposefully placed in intricate patterns so as to benefit from gravity. Your analogy seems to argue for intelligent design. Either way, it's a horrible analogy. sorry = (

  3. Hand-laid stones are purposefully placed in intricate patterns so as to benefit from gravity.

    The challenge is not to build a good wall with a particular set of stones, but to build the best wall possible, the one with the least empty space.

    Can you do it? I believe the task is too complex.

    However, one can set up a situation in which nearly ideal solutions will arise naturally. That's what the vibration is for. Vibration causes things to pack together.

    Google 'genetic algorithm' for another example of natural selection being used to find answers to complex problems.