Animals adapt to new environments. New species develop from survivors. There is variation among individuals within a species. Insecticides may cause genetic mutations.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Five hundred flies of one species were sprayed with a new insecticide. Twenty-four hours later, nearly all the flies were dead. However, a few survived. Which principle best explains why some flies survived?
Possibilities:
- Animals adapt to new environments.
- New species develop from survivors.
- There is variation among individuals within a species.
- Insecticides may cause genetic mutations.

There is variation among individuals within a species.