7.1 Introduction to Natural Selection

Describe the causes of natural selection.

• Natural selection is a major mechanism of evolution.
• According to Darwin’s theory of natural selection, competition for limited resources results in differential survival. Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing on those favorable traits to subsequent generations.

Explain how natural selection affects populations.

• Evolutionary fitness is measured by reproductive success.
• Biotic and abiotic environments can fluctuate, affecting the rate and direction of evolution. Different genetic variations can be selected in each generation.