sentence: Organisms become adapted to the environments they live in.
sentences_before: Darwin thought that most extinctions occurred because some organisms became more effective, and replaced their less advanced competitors. No doubt that does occur, but the view now is that environmental change is  more important.
sentences_after: The environment certainly does change, and sometimes quite dramatically. When it does, some organisms can adapt to the changes, and some cannot. The ones that cannot become extinct.
concept_name: organism
headings: Extinction Reasons
categories: Evolutionary biology Extinction events