How Many Bones In A Giraffe's Neck?

The question is why are there always 7 bones in the neck of mammals?
The functioning of the neck is so critical to life that if one is born with 6 or 8 cervical bones they will surely not live! Infact, of all the mammals, only the super slow moving slouth can live if they are born with 6 or 8 cervical bones!
