"According to most philosophers, we reason ourselves towards a moral position," says Dutch primatologist Frans de Waal. "Even if we do not invoke God, it is still a top-down process of us formulating the principles and then imposing those on human conduct. But would it be realistic to ask people to be considerate of others if we had not already a natural inclination to be so? Would it make sense to appeal to fairness and justice in the absence of powerful reactions to their absence? Imagine the cognitive burden if every decision we took needed to be vetted against handed-down principles. Instead, I am a firm believer in the Humean position that reason is the slave of the passions."