Natural selection the mechanism behind evolution.
Natural selection is Darwin’s mechanism for evolution: heritable traits that suit the environment spread because the individuals carrying them reproduce more. Here is the AP Biology definition, the conditions it needs, the types of selection, and the mistakes to avoid.
The short definition
Natural selection is the mechanism Charles Darwin proposed for evolution: individuals whose heritable traits suit their environment tend to survive and reproduce more, so those traits become more common over generations. It is the process that adapts populations to their surroundings.
The natural selection AP Biology definition that earns points is short: differential reproductive success based on heritable variation, which shifts a population’s allele frequencies over time.
The conditions it requires
Natural selection needs all of these to occur.
Types of selection
The same mechanism can push a trait in different directions.
Why it matters in AP Bio
Natural selection is the backbone of the evolution unit and connects to Hardy-Weinberg, speciation, and phylogenetics. Evidence comes from the fossil record, shared anatomy, DNA comparisons, and observed cases like antibiotic-resistant bacteria and the Galapagos finches. The AP Biology FRQ often gives you data showing a trait changing and asks you to explain it through selection.
Common mix-ups
The biggest error is saying organisms change because they need to. They do not; variation already exists, and the environment simply favors some variants over others. Remember too that natural selection acts on individuals through their phenotypes, but evolution is the change in the population. Fitness means reproductive success, not strength.
Frequently asked questions
Quick answers — written by humans, not a chatbot.
What is natural selection in simple terms?
Individuals with heritable traits that suit their environment survive and reproduce more, so those traits become more common in the population over time.
What does fitness mean in natural selection?
Reproductive success, measured by how many offspring survive to reproduce, not physical strength or size.
What is the difference between natural selection and evolution?
Natural selection is one mechanism that drives evolution. It acts on individuals through their traits, while evolution is the resulting change in the population’s allele frequencies.