Theory of Evolution

Evolution Evolution is the change in allele frequencies in a population over time. Most fundamental concept in Biology. You cannot understand all the parts of Biology without understanding evolution.

Remember alleles? Alleles are the different variations of a particular genetic trait. Allelic frequency deals with how often a particular allele appears in a population.

12 green alleles and 8 brown alleles in this population Allelic Frequency 12 green alleles and 8 brown alleles in this population

Jean Baptiste Lamarck French Naturalist 1809- published ideas on evolution

Lamarck’s Hypothesis During organism’s lifetime, physical features increase or decrease in size based on use disuse Organisms pass down acquired traits to offspring

Copyright Pearson Prentice Hall Lamarck’s Hypothesis Fiddler Crabs Lamarck proposed that the selective use or disuse of an organ led to a change in that organ that was then passed on to offspring. This proposed mechanism is shown here applied to fiddler crabs. (1) The male crab uses its small front claw to attract mates and ward off predators. (2) Because the front claw has been used repeatedly, it becomes larger. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Lamarck’s Hypothesis Lamarck proposed that the selective use or disuse of an organ led to a change in that organ that was then passed on to offspring. This proposed mechanism is shown here applied to fiddler crabs. (1) The male crab uses its small front claw to attract mates and ward off predators. (2) Because the front claw has been used repeatedly, it becomes larger. Copyright Pearson Prentice Hall

Believed that those parts of the body used extensively would become bigger and stronger and would be passed to offspring.

were not used would disappear Those body parts that were not used would disappear Legless salamanders

Thomas Malthus - 1798 Pop. growth limited by disease, famine, war Human population increasing faster than supply of resources

Charles Lyell Leading geologist of Darwin’s time. Believed the Earth was very old and had changed slowly over long periods of time.

Charles Darwin The theory of evolution proposed by Darwin explains how evolution works. He realized that there is a struggle for existence among individuals.

Voyage on the Beagle Darwin was 22 when he set sail on the HMS Beagle as the ship’s naturalist. Spent 5 yrs observing and collecting specimens from jungles, grasslands, desert, etc.

Galapagos Islands Islands of relatively recent volcanic origin that lie on the equator about 900 km west of the S. American coast.

Darwin noticed…

Darwin observed the various adaptations of plants and animals that inhabited such diverse environments.

Darwin’s Finches Darwin collected 13 types of finches that, although quite similar seemed to be different species. Some were unique to individual islands while others were on two or more islands that were close together.

After the Voyage… Spent 20+ years studying collections Results: variations w/in same species enable some to survive & reproduce, while those w/other variations do NOT survive or reproduce

Also studied… Farmers’ breeding of plants & animals with desirable traits Artificial selection - selective breeding of plants/animals w/desirable traits

Origin of Species In 1859, Darwin published his book, The Origin of Species by means of Natural Selection.

Natural Selection Organisms with favorable variations for a particular environment will survive and reproduce —and pass these variations to offspring. “Survival of fittest” Fitness – ability of an organism to survive & reproduce in its specific environment

For example… If a rabbit lived in an environment where it snowed all the time—what color of fur would be more advantageous? Why?

Environment determines which traits are advantageous

Main points of Darwin’s theory of natural selection: Genetic variations exist in populations Overproduction of offspring– struggle for existence (limited resources) Organisms best adapted will survive, reproduce and pass traits to next generation. Ex: hummingbirds with longer beaks.

CONCEPT REVIEW: True or False Changes in the phenotype of a species over time is called evolution. TRUE

CONCEPT REVIEW: True or False 2) An organism can pass down an acquired trait to its offspring. FALSE

Which of the following does not belong with the others? These are people who shaped Darwin’s Thinking. Charles Lyell Thomas Malthus Gregor Mendel Jean-Baptiste Lamarck

Fill in the missing idea There are more offspring than the environment can support Populations have genetic variations These all describe The main points of Darwin’s theory Organisms w/favorable variations will survive, reproduce and pass traits to offspring Struggle for existence

CONCEPT REVIEW: Multiple Choice A farmer’s use of the best livestock for breeding is an example of Natural selection Artificial selection Common descent Extinction

CONCEPT REVIEW: Multiple Choice A farmer’s use of the best livestock for breeding is an example of Natural selection Artificial selection Common descent Extinction

Use the main points of Darwin’s theory of natural selection to explain

Natural Selection Video

Are You Able to… Explain how natural selection causes populations to change over time?? Describe what determines which traits are advantageous??