THEORY OF EVOLUTIONChapter 15

Evolution • Development of new organisms from pre-existing ones• Heritable change in the characteristics within a

population from one generation to the next• Charles Darwin published “On the Origin of the Species”

in 1859• descent with modification (DwM)

Descent with modification (DwM)• Every species must have

descended by reproduction from preexisting species

• Species must be able to change over time

Natural selection• Mechanism for DwM• Four main parts of Darwin’s reasoning

1. Overproduction: more offspring produced than can survive

2. Genetic variation: individual within a population have different traits

3. Struggle to survive: individuals compete• Some variations improve chance for survival and reproduction• Adaptation: trait that makes an individual successful in its

environment

Natural selection

4. Differential reproduction: organisms with best adaptations are most likely to survive and reproduce• Through inheritance, adaptations become more frequent

in a population• This leads to change in a population• Fitness: measure of an individual’s heredity contribution

to the next generation• More than survival• Must reproduce offspring that will reproduce in turn

Notebook assignment: See page 300

Contributors to Darwin• Before Darwin’s time, most

scientist thought the earth and it’s organisms were permanent and unchanging

• Earth was thought to only be thousands of years old• How old is it actually?• About 4.5 Billion years old

• Geologists started to identify the actual age of the earth by looking at the rock strata: rock layers

• Oldest layers on bottom

Contributors • French anatomist Georges Cuvier

• Reconstructed fossils• Some organisms in the past differed greatly form any living

species• “sudden changes” result of CATASTROPHISM >> caused

extinction

• English geologist Charles Lyell• UNIFORMITARIANISM

• the theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes

• French biologist Jean Baptiste Lamarck• INHERITANCE OF ACQUIRED CHARACTERISTICS

• is the idea that an organism can pass on characteristics that it acquired during its lifetime to its offspring

Inheritance of Acquired Characteristics

Fossil record• Fossil: remains or

traces of past life• Fossils show that

different organisms have appeared at different times and places on Earth

• Superposition: oldest rocks on the bottom

How old is it?• Relative vs absolute age• Which is older: A fossil at A or F?• If a radioactive isotope has a half-life

of 50 years, how much is left after 250 years if the original amount was 5,000 mg? Half-lifes Mass

remaining

0 5000 mg

1 (50 years) 2500 mg

2 (100 years

1250 mg

3 (150 years)

625 mg

4 (200 years)

312.5 mg

5 (250 years)

156.25 mg

Transitional species• Intermediate species between ancestral species and later

descendants• Page 304

Biogeography • Studies why living things are found where they are• Unrelated organisms with similar features

Comparative anatomy• Homologous structures: found in related species that

share a common ancestor• May have different functions but similar structure• Analogous structures: related functions, but different

structure

Vestigial structures• Structures with no current function• May have been functional in ancestral species

Evolution in action• Evolution is continuous and

ongoing• Scientists can study

evolutionary patterns today• Case study: anole lizards

• Page 308

Convergent evolution• Process by which different species evolve similar traits

Divergence and radiation• Divergent evolution: process in which descendants of a

single ancestor diversify into species that each fit into different parts of their environment

Adaptive radiation• Many species evolve from a single ancestral species

Artificial selection• Selective breeding of

organisms for specific traits• DONE BY HUMANS!!!• This is in contrast to natural

selection in which the environment places pressure on certain traits

Coevolution

• When two or more species have evolved adaptations to each other’s influence

• Why are flowers different colors?• Why do they have different scents?• Why are flowers shaped differently?• Why do we keep having to develop new antibiotics?• Methicillin Resistant Staphylococcus aureus• MRSA