A scientist has observed animals in a particular habitat for some time. She notices that in a population of birds those with either short or long beaks can find more food than those with average sized beaks. Over time, she notices a higher proportion of birds in the population have either short or long beaks. She is observing:
A - Disruptive selection
B - Heterozygote advantage
C - Balanced polymorphism
D - Directional selection
Answer: A - Disruptive selection
DISRUPTIVE SELECTION is a type of natural selection in which individuals at either end of a phenotypic spectrum are most fit.