Trees need water so they can make their own food. Trees take in water using their roots.
If a drought occurred reducing the amount of available water, some trees, such as those with deep roots that can reach the water table, would be naturally selected over other trees. If the drought continued for an extended period of time, the trees would likely evolve until most of the trees possessed drought-resistant characteristics.
Which of the following allows natural selection and evolution to occur?

A. using other plant parts instead of roots to absorb water

B. differences in the characteristics of individual trees

C. having an identical genetic make-up

D. increasing the height of the water table

Evolution refers to the changes certain species of organisms experience over a long time that is mainly prompted by natural selection which occurs as changes in the environment or conditions make certain traits to prevail over time and others to disappear. This occurs in the case presented as drought makes trees with deep roots prevail over time while other trees disappear. This implies,s the factor that allows natural selection and evolution to occurs is the differences in the characteristics of individual trees or that some of the trees have deep roots that prevail while others with superficial roots tend to disappear.