7.5 Patterns of Selection
Notes
Natural selection can change the distribution of traits in different ways.
- Directional selection favors one extreme (e.g. darker moths when tree bark is darkened by soot).
- Stabilizing selection favors the average (e.g. human birth weight).
- Disruptive selection favors both extremes over the middle.
- Sexual selection favors traits that help attract mates, like a peacock's tail.
Practice
During the Industrial Revolution, soot darkened trees, and dark peppered moths became more common than light ones. This is:
Selection shifted the population toward one extreme (dark color).
Very small and very large human babies have lower survival rates than medium-sized ones. This is:
The average is favored and extremes are selected against.
Male peacocks with large colorful tails attract more mates, even though the tails make them easier for predators to catch. This is:
The trait increases mating success.
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