How come some species of animals are much more intelligent than others and some are much more friendly than others?

Question: How come some species of animals are much more intelligent than others and some are much more friendly than others?
- Keywords:
  friendly,
  intelligent,
  playful
Asked by niamhgreene10 to Charlotte, Jo, Kevin, Louise, Valeria on 15 Jun 2012. This question was also asked by marialovesmusic.
- Joanna Cruden answered on 15 Jun 2012:
  
  It is just nature, even within the same species there will be more intelligent and friendlier individuals. It really is what makes this such a fabulous diverse planet to have so many different species, the carnivores are more aggressive because they need to kill to eat and survive and it does not pay to be friendly to other species because they could be your supper!

Question: How come some species of animals are much more intelligent than others and some are much more friendly than others?