Arat becomes a long tailed rat and a short tailed rat over 1 years. what is this called ?

Evolution

Explanation:

Evolution can be described as the changes which occur in a population over a period of time. Over a period of time, organisms tend to evolve those characteristics which make them better adapted to live in an environment. Such changes which occur over a long period of time are termed as evolution. Charles Darwin was the scientist to bring forward the theory of evolution.

The change in the tail length of a rat over a course of many years is an example of evolution.

that scientist would be robert hooke