Giraffes whose necks are not long enough to reach a good supply
of food will not survive. The giraffes with long necks will survive
and breed and their young will tend to have long necks. Over time
this causes natural selection of giraffes with the most appropriate
The Genus Equus includes horses, donkeys and zebras.
They are mammals, with long heads and necks (with a mane of
hair). They have long, slender legs with a single toe - protected
by a hoof. They are herbivores, that usually feed on fibrous food
such as grass.