Natural Selection Variations and Generational Evolution

What is stabilizing selection, and what does its graph look like?

Stabilizing selection favors the average traits in a population, reducing extremes. The graph shows a higher peak at the average trait. (Example: Human birth weights—medium-sized babies survive better than very small or very large ones.)

What is directional selection, and what does its graph look like?

Directional selection favors one extreme trait over others, causing the population average to shift. The graph shows a peak moving toward the favored trait. (Example: Giraffes with longer necks survive better.)

What is disruptive selection, and what does its graph look like?

Disruptive selection favors individuals at both extremes over the average. The graph shows two peaks at the extremes. (Example: Birds with very large or very small beaks surviving better than medium-beaked ones.)

Compare and contrast stabilizing, directional, and disruptive selection.

Stabilizing favors averages; directional shifts toward one extreme; disruptive favors both extremes but not the average.

How does the length of a generation affect the speed of evolution?

Shorter generations allow for faster reproduction and more mutations, speeding up evolution. (Example: Bacteria evolve resistance quickly due to short generations.)

Why do humans evolve more slowly compared to bacteria?

Humans have long generations, so fewer evolutionary changes can occur over the same period.