17. Which of the following examples of an ecological effect leading to an evolutionary effect is most correct? A) When seeds are not plentiful, trees produce more seeds. B) A few organisms of a larger population survive a drought, and then these survivors emigrate to less arid environments. C) A few individuals with denser fur survive the coldest days of an ice age, and the reproducing survivors of the ice age all have dense fur. D) Fish that swim the fastest in running water catch the most prey and more easily escape predation. E) The insects that spend the most time exposed to sunlight have the most mutations.

Evolution refers to the gradual development of living organisms from earlier forms to the forms that exist today. One of the principal factors that lead to evolution is the ability of an organism to adapt to adverse changes in its environment. Organisms that are able to survive adverse changes in their environments usually go on to produce offspring that possess their parents' ability to survive. A good example of this is given in option C, where individuals with denser fur were able to survive from severe cold and then give birth to young ones that inherit their parents' ability to survive severe cold.