Evolution

Definition of Evolution • A change in species of

organisms over time.• A process by which

modern organisms have descended from ancient organisms.

• The Theory of Evolution is credited to Charles Darwin.

• Actually many scientists developed theories about evolution and contributed to the modern theory.

Early Scientists

1. Lamarck (1800)

Major points to his ideas:

A desire to change:

Use & disuse:

Inheritance of acquired traits:

2. Darwin Overproduction:

Struggle for Existence:

Variation:

Survival of the Fittest:

Evolution of a Population:

Lamarck & Darwin Compared

Lamarck Populations of organisms

all the same (no variations).

Changes occur in the environment.

Organisms can change in response to environment.

All organisms survive.

Darwin Populations of organisms

with individual differences (variations).

Changes occur in the environment.

Environment “selects” for or against certain variations.

Not all organisms survive.

Darwin’s Evidence• In 1831, Darwin was hired as a

naturalist (person who studies nature) aboard the HMS Beagle.

• The voyage would last 5 years and travel around the world.

• At each stop Darwin collected specimens of plants, animals, rocks and fossils. He also kept detailed observations about the specimens and the environment.

• Darwin also studied 3 books – 1) written by his grandfather about differences in individuals, 2) Lyell’s book about geological events, 3) written by Malthus about human population outgrowing the environment.

• When Darwin returned to England he studied how farmers used selective breeding to improve livestock herds and crop plants.

• It took Darwin almost 30 years after his return to write his book The Origin of Species by Natural Selection.

Adaptation

• Process by which populations of organisms become better “fit” (suited to their environment).

• Organisms that are “fit” live longer and produce more offspring (pass on their genetics).

• Darwin used the term “adaptation” to describe any inherited characteristic that increases an organisms ability to survive.

Modern Evidence in Support of Darwin’s Theory

1. Fossil Record• From fossils, scientists

have put together a geologic time scale (earth history).

• Relative dating – determining the age of a rock by comparing it to other fossils in rock layers above or below.

• Absolute dating – using the rate of decay (half-life) of radioactive elements (Carbon-14, Uranium-235, etc.) to determine the age of a fossil.

2. Comparative Embryology

• Comparing the similarities and differences between embryos of different species at early stages of development.

• The more closely related species differences do not appear until very late stages of development.

• The less closely related species are the earlier differences appear.

Fish Chicken Pig Human

3. Comparative Anatomy

• Anatomy = body structure.

• Homologous structures – are similar in structure & function.

• The greater the similarities the more closely related 2 species are.

• Vestigial organs – organs that have no known function (Ex: ?).

4. Comparative Biochemistry

• Chemical makeup of compounds.

• Typical compounds used are DNA, ATP, Hemoglobin, and other proteins.

• More similarities in chemical composition the more closely related 2 species are.

Conclusions • The types of organisms present at a given period of the earth’s history have changed.

• Some organisms are no longer living on earth (extinct).

• As the number of similarities between species increases the more closely related the two species.

Problems of the Fossil Record1. Not Complete – fossils

occur by chance when organisms do not decay (trapped in sediments, tar or tree sap), most organisms decay without forming a fossil.

2. Quality – preservation varies – only part of body, footprints or impression may be fossilized.

3. Age – determining the age of a fossil is not exact – ages are usually approximates and not absolute.

Recent Evidence of Evolution1. Peppered Moths Before

the Industrial Revolution in England peppered moths were mostly light brown but a few were dark. During daylight moths rested on tree trunks which were light colored. During the I.R. soot from burning coal coated trees. How did the population of moths change?

• Frequency of light colored moths in the population decreased.

• Frequency of dark moths decreased.

2. Antibiotic Resistant Bacteria

• Has occurred in the last 80 years.

• Misuse & overuse of antibiotics have contributed to the problem.

• Are several strains of bacteria that have become resistant.

• Examples: include bacteria that cause gonorrhea, TB, and Staph infections. Staph infection

(Flesh-eating Bacteria)

3. Insect Resistance to Pesticides

• Resistant genetics is present in a small number of insects in a population.

• When pesticides are not rotated, the percentage of resistant insects in a population increases.

4. Weed Resistance to Herbicides

• Herbicide are not known to directly cause the genetic change that allow resistance.

• Resistance is present in the population.

• When the same herbicides are used over several seasons, the resistant weeds survive and a greater percentage of the population are resistant.

Sources of Variation in Populations1. Genetic Recombination • Organisms that

reproduce sexually inherit ½ of their genes from each parent, this increases variation in individuals (individual differences).

2. Mutations • Changes in DNA or

chromosomes create variation in individuals.

Important Points to Remember:

1. Changes occur in populations – not in individual organisms.

2. Adaptations only occur if individual differences can be passed on to offspring (inherited).

3. Evolution is any change in the relative frequency of a gene pool of a population.

4. Evolutionary changes only occur in response to changes in the environment.

Important Terms:

1. Evolutionary Fitness success organism has in passing it’s genes on to the next generation.

2. Adaptation any genetically controlled characteristic of an organism that increases it’s fitness.

3. Species group of organisms that interbreed in nature and produce fertile offspring.

Speciation = development of a new species.

• Occurs when 2 populations are isolated (separated) & cannot interbreed. • 2 populations undergo different changes based on the variations in each

population.• After long term separation the 2 populations may develop reproductive

barriers (reproductive isolation).• Once reproductive isolation has occurred the 2 populations are considered

separate species.

Reproductive barriers:

1. Different breeding seasons.

2. Different courtship rituals.

3. Habitat isolation.

4. Offspring not viable (do not live).

5. Offspring sterile.

6. Gametes will not fuse. Fertilized egg not viable (will not develop).

Geographic barriers isolate populations.

1. Rivers2. Mountains3. Oceans4. Canyons5. Roads6. Housing additions

Modifications to Darwin’s Theory

Unchanged Gene Pools

• Some gene pools remain relatively unchanged for long periods of time. Requires:

1. No major changes in the environment.

2. Species is well adapted.

3. No competition by invading species.

Genetic Drift

• A random change in the frequency of a gene in a gene pool.

• Occurs when there is a random environmental event (eruption of a volcano).

• Implies that not all characteristics contribute to fitness.

Punctuated Equilibrium

• Long periods in which there is not change in a population followed by short periods of rapid change. (Ex: peppered moths)

• Is still a controversial theory.• May result from dramatic changes in climate.