So... eating meat makes us soft and tame?

Apparently, tryptophan increases serotonin level, which in turn makes us more happy and agreeable, and eases depression if we had one. Tryptophan is mostly found in protein-based food, such as dairy products and meat. But in order to eat meat we have to harm an animal, and to have milk and egg we need to make animals our slave/friend/domestic companion. Wait a minute. I guess this is a regulation measure by nature?

So I have to eat more meat if I want to be more cheerful.

P.S.: Actually, soybeans work too. I'll go drink more soy milk.