Paleontologists observed changes in the sizes of black bears as their environment changed

Question

During warmer periods between ice ages, most black bears were small. During ice ages, most black bears were large. Which type of selection is this, and how would a graph of the distribution curve of black bear size change as Earth moved out of an ice age? (1 point)
• disruptive; the curve would break into two peaks with a dip in the middle
• directional; the curve would shift to the right
• directional; the curve would shift to the left
stabilizing; the curve would become taller in the middle and shorter on each side

Answer 1

The correct answer is: directional; the curve would shift to the left.

This is because during ice ages, when the environment is colder and resources are limited, larger black bears are more likely to survive and reproduce, passing on their genes for larger size to future generations. As the Earth moves out of an ice age and temperatures become warmer, smaller black bears are favored because they are more energy-efficient. Therefore, the average size of black bears would decrease, causing the distribution curve to shift to the left.