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: individuals that have inherited beneficial adaptations produce more offspring on average than others. 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 There are four main principles to the theory of natural selection. –variation Natural selection explains how evolution can occur. – overproduction – adaptation – descent with modification VARIATION OVERPRODUCTION ADAPTATION Fitness is the measure of survival ability and ability to produce more offspring.

10.3 Theory of Natural Selection Which rabbit is best adapted?

10.3 Theory of Natural Selection Which rabbit is best adapted?

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

10.3 Theory of Natural Selection Natural and artificial selection are not the only factors in evolution. We’ve learned about natural selection and artificial selection, but what about sexual selection? –Mating can have an important effect on the evolution of a population.

10.3 Theory of Natural Selection Sexual selection occurs when certain traits increase mating success. Sexual selection occurs due to higher cost of reproduction for females. –males produce many sperm continuously –females are more limited in potential offspring each cycle

10.3 Theory of Natural Selection There are two types of sexual selection. –intrasexual selection: competition among males –intersexual selection: males display certain traits to females

10.3 Theory of Natural Selection The Peppered Moth Mini-Lab Before the industrial revolution, the trees in the forest around Manchester, England were a light grey/green due to the color of lichens (fungus) on their trunks. Peppered moths, or Biston betularia, which lived in the area, were mostly lightly colored with dark spots. However, there was some color variation between the moths. The most common moth color was light with dark spots and the least common were dark with light spots. Because there were not enough resources to support the entire population, the members of this species had to compete for survival. Their coloring, when against a similar background, served as camouflage against predators such as birds and lizards, thus increasing chances of survival. As the Industrial Revolution progressed, the trees became covered with sulfur dioxide, turning the trunks dark.

10.3 Theory of Natural Selection