"Individual organisms are best thought of as adaptation-executers rather than as fitness-maximizers."—John Tooby and Leda Cosmides, The Psychological Foundations of Culture
If we regarded human taste buds as trying to maximize fitness, we might expect that, say, humans fed a diet too high in calories and too low in micronutrients, would begin to find lettuce delicious, and cheeseburgers distasteful. But it is better to regard taste buds as an executing adaptation - they are adapted to an ancestral environment in which calories, not micronutrients, were the limiting factor. And now they are simply executing that adaptation - evolution operates on too slow a timescale to re-adapt to such a recent condition.
Evolution is ultimately just a historical-statistical macrofact about which ancestors did in fact reproduce. These genes then execute again, as they did previously. And so the behavior of the organism is often better interpreted in terms of what worked in the past, rather than what should work in the future. The organism's genes are, in fact, the causal result of what worked in the past, and certainly not a causal result of the future.