A) I hope it is clear and unchallenged that behavior with regard to food must be at least as primal as behavior regarding mating, sex, pair-boding or social behavior. It is fairly obvious why, like how a huge part of the evolution of many species is about better acquiring food, from the various beak shapes of birds to the fangs of predators. Agreed?

B) The corollary is that IF, I said: IF human feeding behavior can be demonstrated to be not very instinctive, not very biological, but more cultural, then it is fair to say mating, sex, romance, pair bonding, social behavior is also not biological but more cultural? Because there is no way mating can be more biological than feeding. We have similar genitals to what cats have but very different teeth. We eat different, but mate, at least on the physical level, similarly. So mating is less hardcoded than eating, agreed?

The evidence, part 1:

C) The true "paleo" diet was simply everything: http://hells-ditch.com/2012/08/archaeologists-officially-declare-collective-sigh-over-paleo-diet/ while most animals have and had more or less narrow diets, "cavemen" adapted to whatever they could find.

The evidence, part 2:

D) If you feed both animals and humans hot spicy food, both will get used to it and be okay with consuming it over time, yet animals will never prefer it over plain food, while humans will: http://www.npr.org/blogs/thesalt/2015/01/13/376963730/how-do-we-grow-to-like-the-foods-we-once-hated

Conclusion: humans can and did eat biologically anything, have a biological instinct to eat anything, yet evolve all kinds of cultures that tell people to like this kind of food and dislike that kind of food. Animals don't do this. You can make a dog eat hot spicy chili, but you cannot make him like it. But you can make a human.

Corollary: if food preference is not hardcoded in humans, and we agreed that mating and social behavior must be less hardcoded than food preference, then it follows that mating and social behavior is largey cultural.