Questions that might at first blush seem banal may have illuminating answers from an evolutionary perspective. Why do we have a utility function, for example? Perhaps because it permits a plastic response by an individual to circumstances that are unusual or even novel in our evolutionary history. Think of Mother Nature as a principal, a puppeteer, who knows the fitness consequences of various outcomes, say. Nature wishes to enhance the evolutionary success of the individual, the agent, the puppet, where this individual also has some local information. This local information might be about the probabilities with which these outcomes occur in various gambles, say. An evolutionary strategy that fixes an appropriate hedonic scoring system for the outcomes within the agent and then devolves autonomy onto the agent permits the agent to blend together the two components–outcomes and probabilities. In the end, the agent chooses the optimal gamble in a flexible and optimal way, endowed with free will, but bound in an hedonic straitjacket.
To ask: Why do we value food, warmth, even of the intelligent and well-educated is to invite incredulity. “What are you, stupid? If we lack those, we will die and have no offspring. Aren’t you into biology?” But if utility is the solution to this principal-agent problem, and we credit ourselves with the requisite intelligence, then why would the optimal utility not simply be offspring? Why wouldn’t the optimal evolutionary strategy not set offspring as utility and then leave it to the intelligent and autonomous agent to figure out that it would be a good idea to eat to further this goal. Sex would seem messy and awkward, but it would have to be endured too. For the kids.
Again the reason why utility has as arguments goods that are intermediate to the production of offspring, as clearly it must in reality, might be that Nature has information that the individual lacks. Although there are, in principle, be other ways of conveying this information, as a matter perhaps of historical accident, Nature has come to whisper in your ear “Don’t think about it, just eat that cheesecake, bask in the sun, smile at that pretty girl…”