Jurassic Park script:

   http://www.imsdb.com/scripts/Jurassic-Park.html
   

ELLIE (off)
          Dr. Grant!  Dr. Grant!

Grant looks up.

DR. ELLIE SATTLER, late 20's, sharp-eyed, tough if she wants to be, runs
like a gazelle across the arid land.  Exuberant, she leaves a trail of
dust behind her.

She zips by A STUDENT guarding the cordoned area.  He tries to stop her.

  1.  What does running like a gazelle have to do with evolutionary
      biology.  The ARMS RACE between predator and prey.

      Essay needed on how the issues of variation of gazelles regards
      the characters that favor speed would mean that those that were
      faster could more likely escape predators, and thus be selected
      more often to pass on their genes.  Thus the prey gets faster
      over the eons.  

      The predators would also vary in speed capability, and the slowest
      of them would be selected against, while the faster ones would be
      more successful at surviving and reproducing and passing on their
      genes.

      The reciprocal nature of this relationship between predator and 
      prey is key here.  Its a WIN/LOSE relationship.

                            STUDENT
          Dr. Sattler!  Dr. Grant is thinking!

Dr. Grant waves her over enthusiastically with his bone and continues.

                            GRANT
          So, what can we stay for sure?  Stress
          fractures in the heel ...

Uncertain students.  Ellie arrives and immediately gets into it.

                            ELLIE
          She jumps.

Grant turns around to her and smiles.  She's got it.  Other students to
- they knew is all along.
            
  2.  She jumps is concluded based on a study of the fossil record.
      Stress fractures in the heel bone area lead to the hypothesis
      that the animal jumped.

                GRANT
          Right as rain, Ellie.  Now, why did she
          jump?

No answer.  Ellie gives it a try.
 
  3.  Why?  Why?  Why did the creature jump?

                            ELLIE
          A defensive posture against a vicious,
          blood-thirsty T-Rex?

                            GRANT
              (nodding)
          Perhaps.  Or maybe to select the smaller,
          more tender leaves in the higher branches
          with which to suckle her young?

Ellie jumps up.

                            ELLIE
          I bet is was a mating ritual.

Students laugh.  One student eyes Grant's self-conscious smile at Ellie.

  4.  It could have been defensive, to escape other predators.
      It could be to get food, and the assumption is this might
      have been a herbivore leaping to reach higher leaves and 
      branches.
      Or Darwin's sexual selection is a possibility too.  Mating ritual
      to establish dominance with other males or to attract a mate.