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

NGSSS SC.912.L.15.13 Describe the conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success. (MODERATE)

These observations led Darwin to write a book Charles Darwin Darwin set sail on the H.M.S. Beagle (1831-1836) to survey the south seas (mainly South America and the Galapagos Islands) to collect plants and animals. On the Galapagos Islands, Darwin observed species that lived no where else in the world. These observations led Darwin to write a book

Giant Tortoises of the Galápagos Islands Pinta Tower Pinta Island Intermediate shell Marchena James Fernandina Santa Cruz Isabela Santa Fe Hood Island Saddle-backed shell Floreana Hood Isabela Island Dome-shaped shell

http://www.galapagosislands.com

“On the Origin of Species by Means of Natural Selection” Charles Darwin Wrote in 1859: “On the Origin of Species by Means of Natural Selection” Two main conclusions: Species were not created in their present form, but evolved from ancestral species. Proposed a mechanism for evolution: NATURAL SELECTION

Darwin’s Observations Most species produce more offspring than can be supported by the environment Environmental resources are limited Most populations are stable in size Individuals vary greatly in their characteristics (phenotypes) Variation is heritable (genotypes)

moth (Biston betularia) Natural Selection Individuals with favorable traits are more likely to leave more offspring better suited for their environment Example: English peppered moth (Biston betularia)

Click to view animation. Example of directional selection animation. Click to view animation.

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 Pigeon Traits Selectively Bred Pigeons

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 is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

Natural selection explains how evolution can occur. There are four main principles to the theory of natural selection. variation overproduction adaptation descent with modification DESCENT with MODIFICATION ADAPTATION OVERPRODUCTION VARIATION

Variations: Differences in traits Come about by mutations in genes Random Occur in sex cells Passed on to future generations

Over Production Having many offspring increases the chance of survival but also results in competition for resources

Bird Beak Adaptations:

Adaptations: a certain variation suited to a particular environment that allow organisms to survive Inuit people, who live in the extreme cold of the Arctic, have short, stout bodies that conserve heat.

Masai people, who live in the arid lands of eastern Africa, have tall, lean bodies that disperse heat well.

Descent with modification Heritability of adaptations More individuals will have the trait in every following generation As long as the environmental conditions remain beneficial for the trait

Survival of the Fitness Fitness is the measure of survival ability and ability to produce more offspring. Does not mean the strongest!

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