Major Objectives

1. Understand the historical context for evolutionary theory, including Darwin's field research that helped frame his view of life

2. Define Darwinism and Darwin's main ideas from the Origin of Species

3. Discuss examples of natural selection and other evidence for evolution

"Nothing in biology makes sense except in the light of

evolution."

Theodosius Dobzhansky

What is Evolution??

Change in gene frequency in a population

over time

Evolution was resisted by Western culture

-Greek philosophers:

Aristole (scala naturae)

-Natural theology (1700's)

Ladder of Life

Lamarkian Evolution

Figure 22.3 Formation of sedimentary rock and deposition of fossils from different time periods

Figure 22.2 Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago

Figure 22.4 Strata of sedimentary rock at the Grand Canyon

Galapagos Island Finches: Beaks Differed According to Food Supply

Darwin's Intellectual Revolution

Millions of DNA Switches That Power Human Genome's Operating System Are

DiscoveredScienceDaily (Sep. 5, 2012) — The locations of millions of DNA

'switches' that dictate how, when, and where in the body different genes turn on and off have been identified by a

research team led by the University of Washington in Seattle. Genes make up only 2 percent of the human genome and were

easy to spot, but the on/off switches controlling those genes were encrypted within the remaining 98 percent of the genome.

In the mid-1990s, researchers were surprised to discover that fruit flies, mice, and humans who were born missing eye structures had defects in the same gene. This

gene, called Pax6 (or eyeless in flies), is required for normal eye development in all animals with bilateral symmetry. Even in eyes that look very different, Pax6 functions

in much the same way. When placed in a fly, the mouse Pax6 gene activates all the genes necessary to form a normal, functional fly eye (not a mouse eye).

http://www.youtube.com/watch?v=UBQ5a7mCpMs

What the Encode project tells us about the human genome and 'junk ENCODE, the Encyclopedia of DNA Elements, is the most ambitious human genetics project to date. It takes the 3 billion letters described by the Human Genome Project in 2000, and tries to explain them. 

http://www.youtube.com/watch?v=Y3V2thsJ1Wc

Darwinism has a dual meaning

-Evolution as the explanation for life's unity and diversity (descent with modification)

-Natural selection as the cause of adaptive evolution

Figure 22.7 Descent with modification

Darwin's main ideas from "The Origin of Species"

Artificial Selection-selecting desired traits

1. Natural selection is differential success in reproduction

Idea of overreproduction influenced by Thomas Malthus (1798)

1. Differential success in reproduction

Not All Organisms Get To Mate

Why is this important?

2. Natural selection occurs through an interaction between the environment and the variability inherent among the individual organisms making up a population

Why is this important?

3. The product of natural selection is the adaptation of populations of organisms to their environment

How does this result in population change?

How does natural

selection work?

Peppered Moths: Real Natural Selection Example

•Original population: white in color, blended into lichens on trees

•During industrial revolution, lichens died & trees covered in soot

•Lighter moths had higher predation rates, darker moths had high survival rates

•Over time, population became dominated by dark moths

Darwin’s Theory of Natural Selection:

Favorable traits that are heritable become more common in successive generations of a population, and unfavorable traits

that are heritable become less common

If phenotypes have a genetic basis, phenotypes will increase or decrease in frequency

Results in change in gene frequency over time

Darwin’s Theory Lacked Satisfactory Theory of Heredity

• Modern Synthesis (1920-1940):

• Unification of Mendel’s theory of heredity and Darwinian evolution

Evidence for Evolution

Evidence for EvolutionFossil Record

Natural selection

Homologous structures

Molecular Biology-DNA

Islands Vestigial Organs Convergent Evolution

Same skeletal elements, different functions

500 endemic species

Vestigial Organs

Convergent Evolution- The independent development

of similarity between species as a result of their

having similar ecological roles and selection

pressures

Major Objectives1. Do populations or organisms evolve?

2. What are the major differences between microevolution and macroevolution?

3. What are the four main factors that can alter genetic diversity?

4. Identify the three main modes of natural selection.

5. Describe the four main reasons why natural selection cannot produce perfection.

Populations Evolve, Natural

Selection Occurs at the Level of Organisms

Types of Evolution*Microevolution-A change in the gene pool of a population from generation to generation

*Macroevolution-Evolutionary change on a grand scale, encompassing the origin of new taxonomic groups, evolutionary trends, adaptive radiation, and mass extinction

Four Main Factors That Can Alter Genetic

Diversity1) Genetic Drift

A change in a population’s genetic diversity due to chance

Why are small populations so vulnerable to extinction?

Extinction Vortex

Disturbance lowers population size

Reduced Genetic Variability

Reduced ability to survive environmental stochasticity

Founder Effect—example for higher risk of breast or ovarian cancer in women

Four Main Factors That Can Alter Genetic

Diversity1) Genetic Drift

2) Natural Selection

Differential success in reproduction

Four Main Factors That Can Alter Genetic

Diversity1) Genetic Drift

2) Natural Selection

3) Gene Flow

Genetic exchange due to the migration of fertile individuals between populations

Four Main Factors That Can Alter Genetic

Diversity1) Genetic Drift

2) Natural Selection

3) Gene Flow

4) MutationAn accidental change in an

organism's DNA

Natural Selection Common Misconceptions:Not Goal-Oriented or Progressive

• Change follows environmental conditions

"Survival of the Fittest"

-Misleading phrase: Does NOT mean competitiveness contest between individuals

-Darwinian Fitness: the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

Natural Selection Common Misconceptions:Is Specific to Environmental Conditions

• Specific phenotype is only adaptive in a specific environment

Natural selection does not produce perfection

1) Evolution is limited by historical constraints

2) Adaptations are often compromises

3) Not all evolution is adaptive

4) Selection can only edit existing variations

All phenotypic variation is NOT heritablePhenotypes are the result of:

1) inherited genotype 2) environmental influences

Reaction Norms: pattern of phenotypic expression of a single

genotype across a range of environments

Si el Norte Fuera el Sur:

A case of squirrel monkey identities

http://www.youtube.com/watch?v=vI7FYM9_EQE

Table 1: Comparison of Saimiri oerstedii Populations

Characteristic La Cusinga/Manuel Antonio Osa Peninsula

Body weight (grams) F 600; M 750 F 650; M 800

Head colorationfemales - blackmales - gray

females - blackmales - black

Body coloration females & males orangevariable, but generally less brilliant than in Manuel Antonio; more of a copper-yellow

Grooming of infants by mothers common never observed

Spatial associations between resident males

remarkably closeclose, but not as tight as in Manuel Antonio

Concept List

Group Number

Assigned Concepts  

Mechanisms of Evolution

Modes of Action of Selection

SpeciationReproductive

Isolation 

One Founder effect  Allopatric speciation

Temporal isolation  

Two   Disruptive SelectionSympatric speciation

Behavioral isolation  

Three Bottleneck effect Stabilizing selection   Mechanical isolation  

Four   Sexual selectionParapatric speciation

Reduced hybrid viability

 

Five Genetic drift Directional selection   Habitat isolation  

Your Assignment:

Working in your assigned group, use the information from the case study to develop a model of evolutionary divergence between these two populations. You may include as many details as you like in your story or scenario, but you must follow some guidelines:

1. Your model should account for at least some of the data supplied in the case study.  2. Your scenario must incorporate the three assigned concepts from the "Concept List" assigned to your group. For each concept you must demonstrate its relevance to your story.  3. Keep in mind that in an evolutionary “story” you will describe events in your monkey population(s) that may have occurred over very long time periods. Current evidence indicates the ancestors of S. oerstedii arrived in Central America from South America some 500,000 years ago, so you could describe plausible geological or climatic events during that time which are relevant to your scenario. In addition, remember the historical range of S. oerstedii was relatively continuous along the Pacific Coast of Costa Rica and western Panama until only 20 years ago. In other words, S. oerstedii was only very recently confined to the small populations of Manuel Antonio and Corcovado.  4. Your group should submit one written summary of the scenario you come up with to explain this speciation event. Rather than writing the “story” in paragraph form, please use an outline format.

5. Be prepared to present a brief summary of your model to the rest of the class! 

Four Main Modes of Genetic Selection

1) Directional Selection

2) Diversifying/Disruptive Selection

3) Stabilizing Selection

4) Sexual Selection

Directional Selection

Diversifying Selection

Stabilizing Selection

Sexual Selection

Three Main Types of Speciation

1) Allopatric Speciation

2) Sympatric Speciation

3) Parapatric Speciation

Elevational parapatry in the I. floralis group (left/top) and the nepos group +I. orpheus (right/bottom).

Hall J P Proc. R. Soc. B 2005;272:2457-2466

Major Objectives

1. Define the biological species concept and its limitations

2. Understand prezygotic and postzygotic barriers that isolate gene pools of biological species.

Biological Species Concept A species is a population or group of populations whose members have the potential to interbreed with each other in nature to produce viable, fertile offspring.

Lynx rufusLynx canadensis

What about limitations? *Difficult to test reproductive isolation of morphologically similar fossils

*Doesn't address species that reproduce asexually (e.g., bacteria)

*Doesn't address hybrids (e.g., plants, zoo animals)

*Difficult to test reproductive isolation of morphologically living species