Once Upon a time there lived a tower (group) of giraffes on the African Savannah. In the tower, there were shorter giraffes than we see today. They ate small shrubs and trees.
Taller Giraffes begin to appear more frequently through the tower (variation)
Predators were realizing how slow the short giraffes were. This made them easy targets. These predators began focusing on the species for a food source.
Shubbery begins to dwindle to the point of extinction
For the Giraffes to prevent being hunted to extinction, they began to reproduce at a very fast rate. This increased the amount of small shrubbery being consumed by the short giraffe.
Short Giraffes begin to die off (selection)
A new type of giraffe started to show. This new giraffe was tall enough to eat the tall plants, and tall enough to fight back or flee when predators attacked.
All the new offspring ate all of the small plants! This made the giraffes begin to starve.
The short Giraffes don't have enough food to support their offspring. This makes them begin to die off. The small giraffes couldn't survive in their environment any longer and died off or became their own species.