Question

Sort each example to the type of selection it describes.

a. Large black bears survived periods of extreme cold better than smaller ones and so became more common during glacial periods.
b. A population has individuals with either large beaks or small beaks, but few with intermediate-sized beaks. The intermediate-sized beak appears to be less effective at cracking either the large or small seeds that are common to the habitat.
c. Birth weights of most humans lie in a narrow range because babies who are very large or very small have higher mortality.

1. Directional selection
2. Disruptive selection
3. Stablizing selection

Answer 1

a- directional selection

b- disruptive selection

c- stabilizing selection

Step-by-step explanation:

Three types of natural selection exists namely: directional, disruptive/diversifying and stabilizing selection.

- Directional selection is the natural selection in which environmental factors favors one phenotype over the other. Hence, one of the extremes increases in one direction. This is the case in a population of black bears where large black bears survived periods of extreme cold better than smaller ones and so became more common during glacial periods.

- Disruptive selection is the natural selection in which both extremes are selectively favored over an intermediate phenotype. This is the case of a population where individuals with either large beaks or small beaks are favored over a few with intermediate-sized beaks because the intermediate-sized beak appears to be less effective at cracking either the large or small seeds that are common to the habitat.

- Stabilizing selection is that selection in which the average phenotype in a population is favored over the two extremes. In this case of birth weights, most humans lie in a narrow range because babies who are very large or very small have higher mortality. Hence, populations with a narrow range (intermediate) are favored.