it's real easy to look at a behavior that doesn't seem to make sense otherwise and say "oh, duh, signalling". The key is that the behavior doesn't make sense otherwise: it's costly, and that's an indication that, if people are doing it, there's a benefit you're not seeing.

People do all sorts of insane things for reasons other than signaling, though. Like because their parents did it, or because the behavior was rewarded at some point.

Of course, signaling behavior is often rewarded, due to it being successful signaling... which means it might be more accurate to say that people do things because they've been rewarded at some point for doing them, and it just so happens that signaling behavior is often rewarded.

(Which is just the sort of detail we would want to see from a good theory of signaling -- or anything else about human behavior.)

Unfortunately, the search for a Big Idea in human behavior is kind of dangerous. Not just because a big-enough idea gets close to being tautological, but also because it's a bad idea to assume that people are sane or do things for sane reasons!

If you view people as stupid robots that latch onto and imitate the first patterns they see that produce some sort of reward (as well as freezing out anything that produces pain early on) and then stubbornly refusing to change despite all reason, then that's definitely a Big Idea enough to explain nearly everything important about human behavior.

We just don't like that idea because it's not beautiful and elegant, the way Big Ideas like evolution and relativity are.

(It's also not the sort of idea we're looking for, because we want Big Ideas about psychology to help us bypass any need to understand individual human beings and their tortured histories, or even look at what their current programming is. Unfortunately, this is like expecting a Theory of Computing to let us equally predict obscure problems in Vista and OS X, without ever looking at their source code or development history of either one.)