I think masculinity is very subjective. I would not describe it the way you have. Otherwise, I'd be quite masculine, and that's just not true. I am very feminine. If I had a penis, I would immediately be branded sissy. I'm such a girly woman. But the OP asked us to compare human males to other animals, and in doing so, I, and others have taken the qualities of our animal bretheren and transfered them to men. In the animal kingdom, alphas are the ones who put up the best fight when challenged. They then become responsible for all of the things several of us said an man who is an apha male would be responsible for, yourself included. In a word, the alpha is the leader. For humans, this has nothing to do with muscles or penis size.