10 3 Theory of Natural Selection KEY CONCEPT

10. 3 Theory of Natural Selection KEY CONCEPT Darwin proposed natural selection as a mechanism for evolution.

10. 3 Theory of Natural Selection 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

10. 3 Theory of Natural Selection • 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.

10. 3 Theory of Natural Selection Struggle for Survival • Populations would grow geometrically if resources were unlimited. Disease, predation, and limited food supply keep populations smaller. An entire family of small frogs found on the coast of South America is thought to have been wiped out by a deadly amphibian disease. The Darwin's frog and its cousin the Chile Darwin's frog, pictured, have not been spotted for months and scientists believe they are now extinct

10. 3 Theory of Natural Selection Natural selection explains how evolution can occur. • There are four main principles to theory of natural selection. • Fitness is the measure – variation of survival ability and – overproduction ability to produce – adaptation more offspring. – descent with modification ADAPTATION DESCENT VARIATION OVERPRODUCTION with MODIFICATION

10. 3 Theory of Natural Selection Variation • The inherited differences that are the basis for natural selection.

10. 3 Theory of Natural Selection Overproduction • Many offspring increases the chance for survival • But – it results in competition for resources

10. 3 Theory of Natural Selection Adaptation • A variation that allows an individual to survive better than the individuals it competes against.

10. 3 Theory of Natural Selection Descent with Modifications • Heritability of adaptations. • As long as the environmental conditions make a trait beneficial, each following generation will have more individuals with the trait.

10. 3 Theory of Natural Selection 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. five digits wrist bone