Question

Which one of the following criteria is necessary for natural selection to occur? 

A. Individuals show no variation in fitness levels.B. Individuals have the same adaptations.C. Enough resources exist for individuals to survive and thrive.D. A struggle for existence is apparent.

Answer 1

A struggle for existence is apparent, so only the strongest survive.

Answer 2

D. A struggle for existence is apparent.

If a struggle for existence is apparent, natural selection occurs because all of the weak/unfit/unadapted ones die.