The taste of the brain

On Neuroanthropology, dlende talks about the De Araujo paper where mice without the ability to identify sweet tastes still consume more sweet things because their mesolimbic dopamine system is stimulated. He then talks about the "common assumption that what we eat relies on conditioned preference" and how this underlies the theory that our dietary preferences evolved in a sugar- and fat-limited Pleistocene and lead us to obesity and heart disease in modern Western times of plenty. The paper shows that pure calorific content, as well as the mouthfeel of fats and the sweetness of sugar, can drive our consumption. In other words, taste isn't just on the tongue. Um, well, yeah. Of course. I didn't know we didn't know that. Surely no-one seriously thought that the tongue was the only feedback on dietary quality we have? Food preference can't explain pregnancy cravings, or cannibalism under duress, or the sugar rush - and was hunger thought to exist only in the stomach and satiety in the stomach walls? Why assume a highly evolved and billennially robust system has no redundancy? Perception of sweetness is as a proxy for highly bioavailable carbohydrate and the mouse experiments also show that a simple knockout can remove sweetness perception - if that (or learned preferences) was the only way to determine what food is the best fuel for sprinting after game or from tigers then we'd be extinct long before we invented gene knockouts.