WHAT DOES THE WORD EVOLUTION MEAN?

The Theory of Natural Selection consists of the following four major points:

1. There is variation among organisms. 2. Organisms struggle to survive. 3. Organisms overproduce. 4. Natural Selection is always taking place.

Early thoughts on evolved traits…

Jean Baptiste Lamarck believed that evolution occurs as structures develop through use or disappear because of disuse.

CHARLES DARWIN

Darwin observed that the plants and animals on the Galapagos resembled those on the South American coast.

Charles Darwin referred to evolution as “descent with modification.”

Malthus stated that human populations have the potential to increase faster than the available food supply.

Darwin made a key association between his observations and Malthus’ observation: “Individuals that possess superior physical or behavioral attributes are more likely to survive than those that are not so well endowed.”

Natural Selection

Darwin waited 15 years before publishing his ideas on evolution because of the intense criticism of the idea by the government and the church.

Many people were deeply disturbed by parts of Darwin’s book.

Scientists now know that genes are responsible for inherited traits Scientists now know that genes are responsible for inherited traits. Therefore, certain traits become more common in a population because more individuals in the population carry the genes for those traits.

Fossils provide some of the most significant evidence for evolution. Transitional fossils Derived traits Ancestral traits

Comparative Anatomy homologous structures: similar structures in different organisms - Vertebrate limb structure vestigial structures: structures in an organism that are reduced in size or function – human appendix, eyes on a blind rat analogous structures: similar structures in unrelated organisms – bat vs. butterfly wings

Comparative Biochemistry *amino acids *DNA * The fewer differences in two organisms DNA or amino acid sequences, the more closely related they are.

Other evidence Comparative embryology – many related organisms have similar embryonic development Biogeography – how organisms are distributed on earth – provides evidence that similar environments lead to similar organisms

The changing of a species that results in its being better suited to its environment is called an adaptation.

Examples of Adaptations Fitness - # of offspring with one trait as compared to the # of offspring without the trait Camouflage – allows an organism to blend in with its surroundings Mimicry – allows an organism to look like another species Antibiotic resistance – bacteria become resistant to the drugs that once treated them

The Hardy-Weinberg Principle The frequency of alleles in populations does not change unless the frequencies are acted on by some factor that causes change Genetic equilibrium – when the frequency of alleles remains the same Only if – large population, no movement, random mating, no mutation, no natural selection

Factors affecting genetic equilibrium Genetic drift Gene flow Genetic mutation

Punctuated equilibrium Gradualism vs. Punctuated equilibrium For a long time, scientists thought that evolution was a continuous, gradual process. Many now think that there are long periods of no change, alternating with period of rapid change.