Why in the animal world are the males always the ones trying to impress the feamles?

Question: Why in the animal world are the males always the ones trying to impress the feamles?
- Keywords:
  female,
  gender,
  male,
  sexual selection
Asked by rachel1197 to Charlotte, Jo, Kevin, Louise, Valeria on 18 Jun 2012. This question was also asked by michelletherezien.
- Joanna Cruden answered on 18 Jun 2012:
  
  The males can mate with many females, all they want to do is pass on their genes, but females usually can only mate with one male so she has to be more selective. She wants to mate with the male that will give her offspring the best chance to survive so males compete to prove that they have the skills to pass on to their offspring.

Question: Why in the animal world are the males always the ones trying to impress the feamles?