Evolving locomotion

This is another “What I love about the web” moment.
I was reading Pharyngula (as I do so often), and his piece “Evolutionists get all the fun” led me to Mark’s ruthless debunking of yet another piece of creationist rubbish by Granville Sewell, who seems to be holding up the left-hand end of the bell curve of IQ in math professors. But that’s not what this all about. At the top of PZ’s post was a picture:
breve image
And I recognized this picture: it looked as if it came from a video clip that Dan Dennett had shown to us in class last spring. Clicking through the link in Mark’s piece took me to the breve home page:

What is breve?
breve is a free, open-source software package which makes it easy to build 3D simulations of decentralized systems and artificial life. Users define the behaviors of agents in a 3D world and observe how they interact. breve includes physical simulation and collision detection so you can simulate realistic creatures, and an OpenGL display engine so you can visualize your simulated worlds.
breve is available for Mac OS X, Linux and Windows in the download section.

Wonderful – but life is hectic right now, I don’t have time to play with this. Not to worry: if you’re running on a Mac, there’s a breveCreatures screensaver which repeatedly runs 20 trials and evolves the most successful “creatures”. In this case the fitness function is “distance travelled from origin”. So now I can go about my day, checking in occasionally to see how evolution is going.
I have to say, though, that PZ falls into a classic trap in his posting. He writes:

One thing I noted right away in the simplest demo (“Walker.tz”) is that there’s no symmetry imposed on the systems, so the poor creatures are afflicted with four limbs that may each have completely different properties, making them particularly thrashworthy. There really ought to be something in the code to require the two upper forelimbs, for instance, to have identical controls, with some kind of central regulatory circuitry that could impose phase differences. Are there no structuralists and developmental biologists among the coders at breve?

No, no, no, PZ! Symmetry is a consequence of evolution, not a constraint. Suppose the most efficient walker turns out to be asymmetrical?! I’m reminded of Dawkins’ “The Extended Phenotype”, where in Chapter One he quotes Fisher: “No practical biologist interested in sexual reproduction would be led to work out the detailed consequences experienced by organisms having three or more sexes; yet what else should he do if he wishes to understand why the sexes are, in fact, always two?”
Anyway, all Mac users are encouraged to grab breve and indulge in a little desktop evolution.