An elk herd is observed over many generations. most of the full-grown bull elk have antlers of nearly the same size, although a few have antlers that are significantly larger or smaller than this average size. the average antler size remains constant over the generations. which of the following effects probably accounts for this situation? a. directional selectionb. stabilizing selectionc. a bottleneck effect that resulted in low genetic diversityd. a high rate of gene flow

B. Stabilizing selection

Explanation:

When natural selection acts against the extreme phenotypes but favors intermediate variants, it is called stabilizing selection. Stabilizing selection is mostly operative in the population s that are well adapted to the prevailing environmental conditions. Individuals with average or intermediate phenotypes are favored by stabilizing selection.

In the given example, the elk population maintains the antler size over generations. Most of the elks have intermediate-sized antlers while only a few have larger or smaller antlers. Since the average antler size (the intermediate phenotype) is favored over the extreme ones (larger or smaller sized antlers), the population is experiencing stabilizing selection.

the answer is :

he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?