What does Dichotomy mean

Dichotomy is a division of organisms into two groups, typically based on a characteristic present in one group and absent in the other group.

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.