Evolutionary Psychology and, increasingly, behavioral economics spin a lot of intriguing stories explaining foibles and otherwise mysterious behaviors as the byproduct of various tricks nature utilizes to get us to do her bidding.  I am on record in this blog as being a fan of this methodology.  But I also maintain a healthy skepticism and not just at the tendency to concoct “just-so” stories that often ask us to reformulate our theories of huge chunks of evolutionary history just to explain some nano-economic peculiarity.

Instead, when evaluating some theory of how emotions have evolved to induce us to behave in certain ways, skepticism should be aimed squarely at the basic premise.  The theory must come with a convincing explanation why nature would rely on a blunt instrument like emotions as opposed to all of the other tools at her disposal.  These questions seemed especially pressing when I read the following article about depression as a tool to blunt ambitions:

Dr Nesse’s hypothesis is that, as pain stops you doing damaging physical things, so low mood stops you doing damaging mental ones—in particular, pursuing unreachable goals. Pursuing such goals is a waste of energy and resources. Therefore, he argues, there is likely to be an evolved mechanism that identifies certain goals as unattainable and inhibits their pursuit—and he believes that low mood is at least part of that mechanism.

Why not a simpler mechanism:  just have us figure out that the goal is unattainable and (happily) go do something else? Don’t answer by saying that this emotional incentive mechanism evolved before our brains were advanced enough to do the calculation because the existence of an emotional response indicating the right course of action presupposes that this calculation is being made somewhere in the system.

Even granting that nature finds it convenient to do the calculation sub-(or un-)consciously and then communicate only the results to us, why using emotions?  Plants respond to incentives in the environment and they don’t need emotions to do it, presumably they are just programmed to change their “behavior” when conditions dictate.  Why would nature bother with such a messy, noisy, and indirect system of incentives rather than just give us neutral impulses?

Finally, you could try answering with the argument that evolution does not find optimal solutions, just solutions that work.  But that argument by itself can be made into a defense of everything and we are back to just-so stories.