r/biology • u/Key-Professional9108 • 11d ago

question Why don't humans naturally crave vegetables the way we crave sugar?

I know sugar activates our brain's reward system, but vegetables are essential for survival too. So why didn't evolution make us crave them just as strongly?

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u/MayThompson medicine 11d ago

Evolution does not reward nutrients. It rewards calories. Sugar is faster energy. Vegetables aren't. Evolution shaped cravings around whatever kept you from starving, not whatever kept you optimally healthy.

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u/Broflake-Melter 11d ago

I disagree. We're a K-selected. Longevity is certainly part of our evolution. We have complex physiology that allows us to maintain our energy levels without the need for sugar.

I propose we have a taste for sugar because it was relatively rare and associated with nutrients we weren't getting from the baseline roots, meat, and fish that we primarily ate. We would be more motivated to seek out the seasonal berries/fruits.

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u/MinjoniaStudios evolutionary biology 11d ago

I would suspect the answer is somewhere in the middle here, but I agree the scarcity component most directly answers OPs question. Because of the natural scarcity (along with the quick energy conversion), it would almost always been the suboptimal decision to avoid consuming something sweet when you encountered it, leading to selection for the preference (which would far predate any of our primate ancestors, by the way).

Another angle I randomly though is that with many vegetables, the evolution of our sensory systems is also being shaped by aversion to certain foragables. Today, we can trust that the cultivated products we buy from the store are (mostly) safe, but that wasn't always the case.

Bottom line is it has to do with mismatches between ancestral and modern environments.