Transition mutations, which result in substitution of the alternate purine for the original purine, or the alternate pyrimidine for the original pyrimidine, are common than transversion mutations.

an adaptation is a change or process by which an organism takes to be better suited for its environment. for example; migration is a behavioral adaptation, this is needed because birds are not built to last extremely cold climates. there are different adaptations because there are different species needing to adjust to different things, bears don't migrate; they hibernate.