Don't ask why

My mother has always told me never to ask "why" questions. They often lead to confusion, like this:

Lawyer
Why did you rob the bank?

Defendant
Because that's where the money is.

The reason I bring this up is that a similar (but different) thing occurred on Friday in my new tutorial group. We weren't discussing robbing banks - we were discussing the electrical activity of the heart. There was all-round bafflement, until Yours Truly applied my phenomenal powers of anal-retentiveness and solved the problem.

New Tutor
Why is heart conduction delayed at the atrioventricular node?

Studious Colleague
Because the cell membrane at the node has different properties that cause the action potential to have a slower depolarization.

New Tutor
Yes... but why is there a delay?

Studious Colleague
(think: didn't I just answer that question???)

Other Less Studious Colleagues
(thinks: didn't he just answer that question???)

PTR
Are you are asking what is the cause of the delay, or are you asking what is the functional usefulness of the delay?

New Tutor
Ah. Yes, perhaps I phrased that question badly. I meant to ask what is the purpose of the delay.

Studious Colleague
It means that the ventricles beat after the atria do.

This really annoyed me, since one of my pet peeves is teleological explanations in science. Saying that the purpose of the AV node is so that the ventricles contract after the atria is like saying that the purpose of the sun is to warm the surface of the earth. Or the purpose of falling over is to break your leg. Or the purpose of this post is to make you think I'm a pompous git. There's a big difference between purpose, and cause and effect.

Purpose is something that belongs to the shady penumbral world of conciousness. Having purpose involves mental states and prediction of future events and preferences and choices. It has nothing to do with evolution, biology, and all those good things.

What really spun me out was that my tutor would express himself in this way. He's a teacher of anatomy for heaven's sake! I would have thought that this sort of thinking would have been beaten out of him years ago. Evidently not - so we gave him a damn good thrashing and made him say sorry.