Question

What would happed if the back bone is only made up of single bone

Answer 1

It would not be flexible like it's is right now we would not be able to bend or do other kind of activities how we are doing a single long bone cannot bend down or back wards so we would be sitting straight if we would have a long straight bone

Answer 2

It would not be flexible. You would be like a Giraffe's neck. Rigid.