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. 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 fossilsDerived traitsAncestral 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

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.