KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

Several key insights led to Darwin’s idea for natural selection. Darwin noticed a lot of variation in domesticated plants and animals. Artificial selection is the process by which humans select traits through breeding. neck feathers crop tail feathers

Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals. Heritability is the ability of a trait to be passed down. There is a struggle for survival due to overpopulation and limited resources. Darwin proposed that adaptations arose over many generations.

Natural selection explains how evolution can occur. There are four main principles to the theory of natural selection. variation overproduction adaptation descent with modification Fitness is the measure of survival ability and ability to produce more offspring. DESCENT with MODIFICATION ADAPTATION OVERPRODUCTION VARIATION

Natural selection acts on existing variation. Natural selection can act only on traits that already exist. Structures take on new functions in addition to their original function. wrist bone five digits

Formative Assessment What did Darwin hope to learna bout artificial selection by studying pigeons? What are the four principles of natural selection? Why must there be variation in the population in order for natural selection to occur? Explain why the phrase “survival of the fittest” does not accurately reflect Darwin’s concept of evolutionary fitness Why is it said that natural selection acts on phenotypes rather than genotypes? How can you explain that a species has remained the same for millions of years?