Types of Natural Selection

Today scientists see three types of natural selection working on populations as environmental changes occur. One example occurs as a trait moves toward an extreme expression. This is known as DIRECTIONAL SELECTION.

An example of this has been the increase in giraffe's necks over the last several million years. Darwin would say: In the giraffe population that produces more offspring than can survive variations in neck length exist. When the times get tough, such as dry seasons in Africa, giraffes struggle to get enough food. Those with longer necks are more likely to survive because they reach the leaves.