The Theory of Evolution does not say this. In fact, the Theory is predicated on the existence of randomness and adaptation. What you're suggesting is that every behavior has a reason for existence, which is almost the opposite of the Theory of Evolution.

Where else would a behavior come from if it weren't purely molecular? The reason for a behavior might be that it is from a random mutation that even survived by random chance.

Maybe you just evolved to think that.

I wish I weren't a logician!

Your wish has been granted.

I certainly believe that I have!

Then we can never convince each other of anything! But, since we know people convince each other of things routinely, the original premise P is a contradiction, therefore not P.

I'm glad we agree, let's go for drinks.