Chapter 10

Principles of Evolution

10.1 Early Ideas About Evolution

• Buffon – proposed that species shared ancestors instead of arising separately.

• Hutton (geologist) gradualism

• Lamarck – inheritance of acquired characteristics. Giraffes developed long necks by stretching to leaves from trees.

• Lyell (geologist) uniformitarianism

• Wallace and Darwin propose theory of natural selection

10.2 Darwin’s Observations

• Darwin observed differences among island species (finches and tortoises). These differences are called variations.

• Darwin realized that species may be able to adapt to their surroundings.

• Adaptations are features that help organisms better survive in their environments.

10.2

• Darwin observed fossil and geologic evidence supporting an ancient Earth.

• He observed that the fossil of the ancient armadillo resembled living species. He concluded that modern animals may be related to fossilized organisms.

• Fossils of marine organisms high in the Andes Mountains led Darwin to conclude that great change can happen over time.

10.3 Natural Selection

• Artificial selection is the process by which humans change a species by breeding it for certain traits.

• In natural selection the selective agent is the environment.

• Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

10.3• Thomas Malthus (economist) proposed that

resources (food, water, and shelter) were natural limits to population growth. Darwin’s struggle for survival.

• A population is all the individuals of a species that live in an area.

• Fitness is a measure of the ability to survive and produce more offspring relative to other members of the population in a given environment.

• Natural selection acts on phenotypes, or physical traits, rather than on genetic material itself.

10.3

• Four main principles to the theory of natural selection:

1. Variation

2. Overproduction

3. Adaptation

4. Descent with modification

10.4 Evidence of Evolution

• Fossil – a trace of an organism that existed in the past.

• Biogeography – the study of the distribution of organisms around the world.

• Embryology – the similarity of early embryos of different species of vertebrates suggests evolution from a distant common ancestor

10.4 Evidence continued• Comparative Anatomy

1. Homologous structures have features that have different functions, but similar structure

2. Vestigial structures are remnants of organs that had a function in an early ancestor.

Example – wings of an ostrich

3. Analogous structures are structures that perform a similar function but are not similar in origin.

10.5 Evolutionary Biology Today• Molecular and genetic evidence support

fossil and anatomical evidence

- Two organisms that are closely related would have very similar DNA sequences.

- Protein sequences in one organism that resemble those of another suggest a shared ancestry.

• Evolution unites all fields of biology.

Chapter 11

The Evolution of Populations

11.1 Genetic variation in a population increases the chance

that some individuals will survive.• Natural selection acts on phenotypes in a

population.• Genetic variation is stored in a population’s

gene pool (all alleles of all of the individuals in a population)

• Allele frequency is a measure of how common a certain allele is in the population.

Genetic variation comes from several sources

• Mutation is a random change in the DNA of a gene. Introduces new alleles to a gene pool.

• Recombination occurs during meiosis when new allele combinations form.

11.2 Natural selection acts on distributions of traits

• Normal distribution - frequency is highest near the mean value and decreases toward each extreme

Natural selection can change the distribution of a trait in one

of three ways• Directional selection

favors phenotypes at one extreme of a trait’s range. P. 331

• Stabilizing selection favors the intermediate phenotype. P. 332

• Disruptive selection favors both extreme phenotypes. P. 333

11.3 Other Mechanisms of Evolution P. 342

• Gene flow is the movement of alleles between populations.

• Genetic drift is a change in allele frequencies due to chance. (Small populations)Bottleneck effect is a genetic drift that occurs after an event greatly reduces the size of a population

Founder Effect p. 337

• Founder effect is genetic drift that occurs after a small number of individuals colonize a new area.

Sexual selection occurs when certain traits increase mating

success. P. 342

• Intrasexual selection involves competition among males, such as the head-butting of bighorn sheep.

• Intersexual selection occurs when males display certain traits that attract the female, such as peacocks fanning out their tails.

Hardy-Weinberg equilibrium: describes populations that are notevolving.

Why is it important: It gives a framework for testing the factors that can lead to evolution.

Five Conditions Required to be in Equilibrium PAGE 3401. Very large population. No genetic drift can occur.2. No emigration or immigration. No gene flow can occur.3. No mutations. No new alleles can be added to the gene pool.4. Random mating. No sexual selection can occur.5. No natural selection. All traits must equally aid in survival.

Hardy-Weinberg equation: p2 + 2pq + q2 = 1

What it means: frequency of AA (p2) plus the frequency of Aa (2pq) plus the frequency of aa (q2) = 100% of the population.How it is used: It is used to determine if a population is evolving.

There are five factors that can lead to evolution P. 343

1. Genetic drift. Allele frequencies can change due to chance alone.

2. Gene flow. The movement of alleles from one population to another changes the allele frequencies in each population.

3. Mutation. New alleles can form through mutation. Create genetic variation.

4. Sexual selection. Traits improve mating success. These alleles increase in frequency.

5. Natural selection. Certain traits may be an advantage for survival. They increase in frequency.

11.5 Speciation Through Isolation

• Reproductive isolation occurs when members of different populations can no longer mate successfully with one another.

• Reproductive isolation is the final stage of Speciation.

• Speciation is the rise of two or more species from one existing species.

• Speciation can be caused by (1) behavioral isolation (2) geographic isolation (3) temporal isolation

11.6 Patterns in Evolution

• Convergent Evolution - evolution toward similar characteristics in unrelated species,resulting from adaptations to similar environments. Example - analogous structures such as wings on birds and insects.

• Divergent Evolution - evolution of one or more closely related species into different species; resulting from adaptations to different environments. Example - Darwin’s finches.

More Patterns

• Coevolution is the process in which two or more species evolve in response to changes in each other.

Beneficial relationships: acacia plant (provides food and housing) and stinging ant (protects from herbivores)

Evolutionary arms race: crab and snail (as snail’s shell gets harder, crab’s claws get bigger and stronger)

Extinction: elimination of a species from Earth

• Background extinction: occur continuously but at a very low rate.

• Mass Extinction: are rare and usually occur as a result of a catastrophic event. Earth has had five known mass extinctions.

Speciation often occurs in patterns.

• Punctuated equilibrium (1972) bursts of evolutionary activity are followed by long period of stability.

• Darwin believed in gradualism (new species arise through gradual transformations of ancestral species.)

• Adaptive radiation is the diversification of one ancestral species into many descendent species.

Chapter 12 The History of Life

Era Period End date

Cenozoic Quaternary Present

Tertiary 1.8

Mesozoic Cretaceous 65

Jurassic 145

Triassic 208

Paleozoic Permian 245Carboniferous 290

Devonian 363

Silurian 410

Ordovician 440

Cambrian 505

Precambrian Vendian 544

Geologic Time Line

Questions

1. How many geologic Eras are shown on the time line?

2. How many geologic period? Which period is the earliest?

3. How many years did the Devonian period last?

Miller-Urey Experiment

1. What do the electrodes simulate?

2. What is the purpose of combining the water vapor and the mixture of gases?

3. What conclusions can be drawn from the mixture that was collected in the container on the bottom?

12.3 Origin of Life

• Several sets of hypotheses propose how life began on Earth

1. Organic Molecule Hypothesis - Miller-Urey Experiment. Early atmosphere contained methane, ammonia, hydrogen and water vapor. Spark produced amino acids.

2. Meteorite hypothesis

3. RNA as Early Genetic Material - discovery of Ribozymes supports this hypothesis (Figure 12.11)

12.4

• Eukaryotic cells may have evolved through endosymbiosis - large prokaryotes took up smaller simple prokaryotes that became mitochondria and chloroplasts

• The evolution of sexual reproduction led to increased diversity.

1st prokaryotes and eukaryotes produced asexually (offspring had same genes as parent)

Sexual reproduction allows new combinations of genes to come together creating greater genetic variation

12.5 Radiation of Multicellular Life

• Life moved onto land during the Paleozoic era

Cambrian period - huge diversity of animal

species evolved - Cambrian explosion

Carboniferous period - coal formed

Era ended with a mass extinction.

• Reptiles radiated during the Mesozoic era

Triassic ended in a mass extinction.

Jurassic had the radiation of dinosaurs.

Cretaceous ended with the mass extinction of dinosaurs.

Mammals radiated during the Cenozoic era

• Tertiary period - primates evolved. Dramatic radiation of mammals.

• Quaternary period – Homo sapiens appeared about 100,000 years ago

• Figure 12.18 Evolutionary Relationships of Primates

• Figure 12.20 Examples of Hominid Skulls