First of all, I want to say that this has been really helpful, I don't want to sound ungrateful and it isn't my intention to have a debate on an topic that I don't know that well. Also, what you say about grand narratives is true, but, the point is, that that wasn't my objective. The reason I asked these questions is neither about biology nor it has to do with animals (even if it refers to them), it is purely philosophical. To be more specific, I'm trying to put in a different perspective some key concepts of contractualism, utilitarianism and natural law.