why does it take such a long time for a species to evolve?

Question: why does it take such a long time for a species to evolve?
- Keywords:
  animal,
  evolution,
  human,
  species,
  time
Asked by 29905340hw to Katie on 19 Jun 2011.
- Katie Marriott answered on 19 Jun 2011:
  
  Evolution occurs due to tiny mutations, or changes, in DNA. If this change is advantageous to the species the individual is more likely to survive long enough to pass on it’s genes to offspring. It takes a long time for these changes to spread throughout a species.

Question: why does it take such a long time for a species to evolve?