Final answer:
According to most evolutionary biologists, disruptive and stabilizing selection are the most common forms of selection. However, this does not mean that genetic variability in natural populations is much lower than expected, as option A suggests. Instead, disruptive and stabilizing selection results in genetic variability in natural populations being much greater than expected.
Step-by-step explanation:
According to most evolutionary biologists, disruptive and stabilizing selection are the most common forms of selection. However, this does not mean that genetic variability in natural populations is much lower than expected, as option A suggests. Instead, the correct answer is option D: disruptive and stabilizing selection results in genetic variability in natural populations being much greater than expected. Both disruptive and stabilizing selection can increase genetic variation within a population, with disruptive selection favoring extreme phenotypes and stabilizing selection favoring average phenotypes.