The problem is that now with our advanced society, we also have a lot of manmade substances with extra dopamine in them. We created things that were even more pleasurable than eating or sitting by a warm fire and these things gave us extra hits of dopamine. The brain still has this reward system and it still seeks out dopamine. It still thinks that dopamine is the most important thing. And so I'm going to be motivated to go and find food and eat food because I get dopamine. You have sex and you get dopamine and your brain says, yes, this is important. I am going to go seek out sex so that I get more dopamine.