Hi. First of all thanks for the immensely helpful summary of the literature!

Since you have gone through so much of the literature, I was wondering if you have come across any theories about the functional role of happiness?

I'm currently only aware of Kaj Sotala's post some time ago about how happiness regulates risk-taking. I personally think happiness does this because risk-taking is socially advantageous for high status folks. The theory is that happiness is basically a behavioural strategy pursued by those who have high status. As in, happiness is performed, not pursued. Depression and anxiety would be the opposite of happiness. I remember some studies showing how in primates the low status ones exhibit depression-like and anxious behavior.

It may simply be my ignorance of the literature, but it seems strange that all these (otherwise wonderful) empirical investigations into happiness are motivated only by a common folk theory of its function.