This is an example of disruptive selection, where the extremes of a trait are favored over the average. In this case, the smaller black bears are favored during warmer periods, while the larger black bears are favored during ice ages.
As the earth moved out of an ice age and into a warmer period, the distribution curve of black bear size would shift towards the smaller end of the spectrum. The percentage of small black bears would increase, while the percentage of large black bears would decrease. Over time, the average size of black bears would decrease as the smaller individuals have a higher chance of survival and reproduction.
Paleontologists observed changes in the sizes of black bears as their environment changed. 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 bears size change as earth moved out of ice age?
1 answer