An Introduction to Evolution(Main Source: University of California Museum

of Paleontology Website)

• The Definition:Biological evolution, simply put, is descent with modification (Darwinian evolution).

• Evolution is currently defined as a change in the gene frequencies of a population through generations. Evolution occurs when population composition changes.

• Macroevolution and Microevolution

An Introduction to Evolution

• Biological evolution is not simply a matter of change over time

An Introduction to Evolution

• The central idea of biological evolution is that all life on Earth shares a common ancestor

The History of Life:Looking at the Patterns

• The central ideas of evolution are that life has a history—it has changed over time—and that different species share common ancestors.

The Family Tree

Descent with Modification 1. Beetles on a diet

Imagine a year or two of drought in which there are few plants that these beetles can eat. All the beetles have the same chances of survival and reproduction, but because of food restrictions, the beetles in the population are a little smaller than the preceding generation of beetles.

Descent with Modification2. Beetles of a different

colorMost of the beetles in the population (say 90%) have the genes for bright green coloration and a few of them (10%) have a gene that makes them more brown. Some number of generations later, things have changed: brown beetles are more common than they used to be and make up 70% of the population.

Which one is an example of evolution?

Mechanisms: The Processes of Evolution

• Mutation • Natural selection • Genetic Variation

as the main factor for Evolution to happen!

• “Founders’ effect”• Mutations are

random.

Natural Selection

• Imagine a population of beetles:

1. There is variation in traits.

2. There is differential reproduction.

3. There is heredity.

Natural Selection

• End result:

Natural Selection at Work

Role of Fitness in Evolution

Sexual Selection and Fitness

• Sexual Selection Process (most of the time in animals): any structural, morphological, behavioral display of MALES to attract FEMALES.

Male Competition and Female Choice!

Lines of Evidence: the Science of Evolution

• James Hutton & Gradualism

• Georges Cuvier & Catastrophism

• Charles Lyell & Uniformitarianism

Fossil Record

Transitional Forms (1 of 2)

Transitional Fossils (2of 2)

Homologies and Analogies

• Homology: similarity in characteristics resulting from a shared ancestry

• Analogy: similarity of structure between two species that are not closely related; attributable to convergent evolution

Anatomy (1 of 2)

Anatomy (2 of 2)

Comparative Anatomy

• Modification of tetrapod skeleton

Developmental Biology (1 of 2)

• Snakes have legged ancestors

• Cretaceous snake Pachyrhachis

problematicus

Developmental Biology (2 of 2)

• Baleen whales have teeth in the early fetal stage and lose them before birth

Cellular/Molecular Evidence

Artificial Selection, Ecology, Experiments, Nested Hierarchies

1. What happened to the two kingdoms I learned about last year?

2. What’s the big deal about homologies?

3. Someone told me that Linnaeus’ classification system isn’t accurate. Why is that?

4. I forgot what a clade is?

5. Why did you say birds are tetrapods when they only have two legs?

6. I have 3 first cousins and 2 second cousins. How can chimpanzees be my cousins too?

7. Should I be taking notes?

8. Would you explain the difference between “homologous” and “analogous” again?