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Evolution & History of Life- Chapters: 22-26

Chapter 22: Darwinian View of Evolution

Chapter 23: Microevolution &Allele frequency changes in Populations

Chapter 24: Macroevolution (Speciation)

Chapter 25 & 26: Mapping out the History of Life through systematics & Phylogenic relationships.

Chapter 22: Darwinian Evolution (The Beginning)

Charles Darwin:-Born in England

-Medical School

-Clergyman

-Naturalist (botany)

-Explorer (HMS Beagle)

http://www.pbs.org/wgbh/nova/id/program.html

Introductory Questions #11) Why is evolution such a controversial subject?2) Name the key founders (original people) for the idea

evolution.3) Name four major pieces of evidence that Darwin

considered in formulating his theory of natural selection. 4) Name three people that influenced Darwin’s thinking as

he developed his theory.5) Name the four key observations Darwin made.6) Why is fossil evidence considered the “most direct”

evidence for evolution? Approximately, how many fossil species have been discovered?

7) What are the three methods for generating a date of a fossil?

Descent with Modification (Evolution)

Evolution: the change over time of the genetic composition of populations

Natural selection:populations of organisms can change over the generations if individuals having certain heritable traits leave more offspring than others (differential reproductive success)

Evolutionary adaptations:a prevalence of inherited characteristics that enhance organisms’ survival and reproduction

November 24, 1859

Introductory Questions #11) Why is evolution such a controversial subject?2) Name the key founders (original people) for the idea

evolution.3) Name four major pieces of evidence that Darwin

considered in formulating his theory of natural selection. 4) Name three people that influenced Darwin’s thinking as

he developed his theory.5) Name the four key observations Darwin made.6) Why is fossil evidence considered the “most direct”

evidence for evolution? Approximately, how many fossil species have been discovered?

7) What are the three methods for generating a date of a fossil?

Major Issues & Questions about Evolution• Our Concept of time is obscure: putting into

perspective and grasping the significance of long periods of time such as 100 yrs? 1000yrs? 10,000yrs? Or even a million years.

• The most difficult concept that Darwin proposed was that all living things are related by a common ancestor.

• How would respond to this question?– When studying life do you include man with all

living things or do you separate man?

Evolutionary History• Linnaeus: taxonomy (binomial Nomenclature)• Hutton: gradualism• Lamarck: Use & disuse (acquired Charact)• Malthus: populations & resources• Cuvier: Paleontology (fossils)

• Lyell: uniformitarianism

• Darwin: Natural selection

• Mendel: inheritance

• Wallace: natural selection

Historical Perspectives on Evolution

• Aristotle Species are “fixed” & unchanging• Linnaeus Founder of taxonomy (binomial nomenclature)• Cuvier Began the study of fossils (Paleontology)

Catastrophism• Charles Lyell Uniformitarianism-same process occur today• Hutton Gradualism• Erasmus Darwin Environment changes causes life to evolve• Lamarck Law of use & disuse, inheritance of acquired

characteristics• Henslow Darwin’s mentor at Cambridge (Botanist)• FitzRoy Captain of HMS Beagle• Malthus Populations struggle for resources

(competition)• Wallace formulated same theory of natural selection

• Lyell (Geologist)Lyell (Geologist)

– Earth was ancient & ever-Earth was ancient & ever-changingchanging

Influences on Darwin’s TheoryInfluences on Darwin’s Theory

• Malthus Malthus (Economist)(Economist)

–““Survival of the Survival of the Fittest”Fittest”

• Political & Political & Philosophical Philosophical RenaissanceRenaissance

Influences on Darwin’s TheoryInfluences on Darwin’s Theory

Video Clip

Observations made by Darwin• Variations exist in the population (heritable)• Reproduce Exponentially (if all are successful) • Populations tend to be stable• Resources are (become) limited• Differential Reproductive success (selection)• Artificial selection (breeding) modifies adaptations

• Noted subtle differences in Noted subtle differences in finches & tortoises, by island & finches & tortoises, by island & compared to mainlandcompared to mainland

Galapagos IslandsGalapagos Islands

Adaptions to Environment

Phylogenetic Tree of Darwin’s Finches

Common Ground Finch

Examples of Descent with Modification

Based on Fossil Evidence

Major pieces of Evidence for Evolution

• Biogeographical Distribution• Comparative Anatomy (homologous structures & vestigial

organs)

• Comparative Embryology• Fossils

Post Darwin: “Neo Darwinism” also called synthetic theory• Molecular Genetics: DNA/Amino acid Sequencing• Chromosomal Changes• Mutations

Evolution evidence: Biogeography

• Geographical distribution of species

• Examples:Islands vs. Mainland

Australia

Continents

These organisms evolved independently of each other in similar environments

Evolution Evidence: Comparative Anatomy

• Homologous structures (homology)

• Descent from a common ancestor

• Vestigial organs Ex: whale/snake hindlimbs; wings on flightless birds

• Convergent EvolutionConvergent Evolution due to similar due to similar niches-same niches-same structures form w/same purposesstructures form w/same purposes

Similar characteristics formed from similar environments with different original structures.

Structures are used for a similar function

**Similar structure different origin

Evolution Evidence: Comparative Embryology

• Pharyngeal pouches, ‘tails’ as embryos

Fossil Evidence

Fossils: remains and traces left behind by organisms-most direct evidence for evolution-provides a record of ancient organisms that have existed-able to generate a timeline-observe the presence of vestigial structures-ancestral descent and lineages can be generated-more aquatic fossils vs. terrestrial have been found

Types of Fossils: imprints, hair, nails, tissue, and other remains

Locations: sedimentary rock, ice, amber, tar, quicksand, petrification

Evolution Evidence: The Fossil Record

• Succession of forms over time

• Transitional links• Vertebrate descent

Dating Fossils

• Location within the rock strata (use index fossil)

• Radioactive isotopes (half-life)– K40 half life is 1.3 billion years argon– U235 half life is 704 million years → lead – U238 half life is 4.5 billion → lead – C14 half life is 5730 years nitrogen

Extinct Whale w/ small hind limbs

Evolution of the Horse

Issues/Arguments with Fossil Evidence

• Record is Incomplete• Transitional fossils are lacking• Dating techniques are not very accurate (wide ranges)• Fossils are difficult to find

– Conditions must be perfect to form & remain intact

• Provides evidence of species that existed but are now extinct (ex. dinosaurs)

• What if fossils were never found?

Evolution Evidence of Today & Molecular Biology

• Similarities in DNA, proteins, genes, and gene products

• Common genetic code

Human Chromosome #2Human & Chimp Comparison of Chromosome #2http://www.teachersdomain.org/special/evol07-ex/

Molecular evidence for common Ancestry

Introductory Questions #31) What is meant by homoplastic features?2) Organisms that are from separate ancestries adapt to their

environments similarly from similar structures. This is an example of .

3) How many vestigial structures have been observed in humans. Name three of them.

4) Why is biogeography (distribution of species) important evidence for evolution?

5) Why is the chimpanzee considered to be the closest living relative of humans?

6) How is a phylogenetic tree generated and what sort of information does it provide?

Key Points to Remember

• A population evolves, not an individual organism• Natural Selection occurs through interactions between individuals• Variations in a population are heritable that are not “acquired in

their lifetime” • Natural selection is the “mechanism” of evolution• The accumulation of small gradual changes over long periods of

time results in larger changes (adaptations)• A new species emerges with slightly different characteristics usually

because of being isolated. (Galapagos Islands)• How and why organisms are able to transmit heritable traits to the

next generation was not explained by Darwin.• Evolution can only modify existing structures.

Final words…...

• “Absence of evidence is not evidence of absence.”

Chapter 23-Microevolution

Population genetics• Population:

a localized group of individuals belonging to the same species

• Species: a group of populations whose

individuals have the potential to interbreed and produce fertile offspring

• Gene pool: the total aggregate of genes in a

population at any one time• Population genetics:

the study of genetic changes in populations

• Modern synthesis/neo-Darwinism• “Individuals are selected, but populations

evolve.”

Hardy-Weinberg Principle• Model proposed in 1908• Represents an ideal situation• Seldom occurs in nature• Mathematical model is used to compare populations• Allows biologists to calculate allele frequencies in a

population• Serves as a model for the genetic structure of a non-evolving population (equilibrium)Represents “genetic equilibrium”If the allele frequencies deviate from the predicted values of HW then

the population is said to be evolving.

Hardy-Weinberg Theorem

5 conditions for Equilibrium

-Very large population size

- No migration

- No net mutations

- Random mating

- No natural selection

**when all these are met then a population is not evolving

Hardy-Weinberg Equation

• p=frequency of one allele (A); q=frequency of the other allele (a)

• p+q=1.0

• (p=1-q & q=1-p)

• P2=frequency of AA genotype

• 2pq=frequency of Aa

• q2=frequency of aa genotype;

p2 + 2pq + q2 = 1.0

Solving & Analyzing HW Principle• Problem: If you had 90 individuals that possessed the recessive

condition in a population of 1000 individuals, determine the frequency of dominant and recessive alleles present in the population as well as the genotypic and phenotypic frequencies.

(1) Always start with the # of homozygous recessive alleles - aa = 90 and q2 = 90/1000 which is 0.09 - a = square root of 0.09 which is 0.3 - A = (1 – 0.3) which is 0.7 - AA = (0.7) 2 which is 0.49

- Aa = ???

**Remember that p2 + 2pq + q2 = 1 (AA) (Aa) (aa)

Microevolution

• Involves small or minor changes in the allele frequencies within a population

• Five processes have been identified:– Nonrandom mating (inbreeding & assortative mating)– Gene flow (migration between populations) – Genetic drift (bottleneck effect)– Mutations (unpredictable change in DNA)– Natural selection (differential reproduction)

**certain alleles are favored over others in nature

Microevolution

A change in the gene pool of a population over a succession of generations

Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability)

Molecular Clock-Pg 385• Used to estimate the time of divergence between two

closely related groups when their common ancestor could have been present.

• Mutations tend to occur at a steady uniform rate over millions of years for closely related species.

• These alterations in the DNA sequence used with geological data

• Allows scientists to reconstruct the evolutionary history of a group and describe its phylogeny

• A single molecular clock for all genes and all species cannot be established. (Why?)