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Chapter 15 Evolution. 15-1 Darwin’s Theory of Natural Selection. Charles Darwin 1809-1882. As a boy liked nature study Flunked out of med school Theology degree from Christ College, Cambridge Became minister Church of England 1831 job as naturalist on HMS Beagle

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Chapter 15 evolution

Chapter 15 Evolution

15-1 Darwin’s Theory of Natural Selection

Charles darwin 1809 1882
Charles Darwin1809-1882

  • As a boy liked nature study

  • Flunked out of med school

  • Theology degree from Christ College, Cambridge

  • Became minister Church of England

  • 1831 job as naturalist on HMS Beagle

  • 5 year world voyage to chart coasts

Unique galapagos islands
Unique Galapagos Islands

  • 1000 km off west coast of South America

  • Unique species animals, similar to S.A. but not exact

  • Unique species animals on each island, similar to S.A. and each other but not exact

Darwin s finches
Darwin’s Finches

  • Especially interesting is the number and variety of these birds

  • Each island had own variety dependent on the food source

Darwin s influenced by
Darwin’s Influenced by:

  • Thomas Malthus: human species grows faster than food supply; competition for food, space, mates, shelter; struggle to survive

  • Pigeon breeding: found individual variation, could breed desirable traits into a population (artificial selection)

  • His 13 children: found individual variation

  • 22 years of study after HMS Beagle to formulate his ideas

Natural selection
Natural Selection

  • Is a mechanism for change in a population

  • Groups NOT INDIVIDUALS evolve

  • Occurs when organisms with certain variations survive, reproduce, and pass their variations onto the next generation

Theory of natural selection old

Individuals in a population have variations

D. Overtime, individuals with helpful variations make up more and more of the population

Organisms produce more offspring than can survive

Individuals with certain helpful variations survive in their environment, reproduce, and pass helpful variation on to offspring

Theory of Natural Selection (old)

15.1 Darwin’s Theory of Natural Selection

Natural Selection (NEW)

  • Individuals in a population show variations.

  • Variations can be inherited.

  • Organisms have more offspring than can survive on available resources.

  • Variations that increase reproductive success will have a greater chance of being passed on.

Origin of species by means of natural selection

Origin of Species by Means of Natural Selection

By Charles Darwin

Published in 1859

Other s ideas on evolution
Other’s Ideas on Evolution

  • Alfred Wallace: had same ideas about natural selection as Darwin, but Darwin published first (both presented their ideas in 1858 at a scientific meeting)

  • Genetics has changed ideas about evolution; now we measure frequency of allele in gene pool

  • Gene pool: all the genes of a population

Chapter 15 evolution1

Chapter 15 Evolution

15-2 Evidence of Evolution

Evolution and natural selection
Evolution and Natural Selection

  • Darwin’s theory of natural selection is not synonymous with evolution.

  • It is a means of explaining how evolution works.

  • The theory of evolution states that all organisms on Earth are related; share a common ancestor.

Evidence for evolution
Evidence for Evolution

  • Fossils

  • Anatomy

  • Embryology

  • Biochemistry

  • Geographic Distribution

  • Adaptations

1 fossils
1. Fossils

  • Record of early life

  • Ancestors of whales were dog sized land animals

  • Record is incomplete

2 anatomy
2. Anatomy

  • Homologous structures: similar arrangement or function or both

    Evidence that organisms evolved from a common ancestor

    (Analogous structures: body parts do not have common evolutionary origin but have similar function)

2 anatomy1
2. Anatomy

B. Vestigial structures: body part that has no function today but probably did in ancestor

eyes of blind mole rat

eyes of blind cave fish

wings of flightless birds

human appendix, little toe, muscles to move ears…

3 embryology
3. Embryology

  • Embryo: earliest stage of growth and development

  • Similarities for all vertebrates

    • Tail

    • Gill slits

      Suggest a common ancestor

Gill slits


4 biochemistry
4. Biochemistry

  • Comparison of DNA, RNA, and/or proteins

  • Newest RNA evidence is that there are three types (Domains) of organisms













Ancestral Prokaryote

5 geographic distribution
5. Geographic Distribution

  • The distribution of plants and animals that Darwin saw first suggested evolution to Darwin.



5 geographic distribution1
5. Geographic Distribution

  • Patterns of migration were critical to Darwin when he was developing his theory.

  • Evolution is intimately linked with climate and geological forces.

  • Biogeography is the branch of science that studies the world distribution of organisms.

6 adaptations
6. Adaptations

Any variation that helps an organisms’ chance for survival

  • Structural Adaptations: can take millions of years

    mimicry: enables one species to resemble another species;

    harmless look like harmful

    all harmful look alike

6 adaptations1
6. Adaptations

  • Structural Adaptations

    camouflage: enables species to blend in with surroundings so that they are not easily found by predators

6 adaptations2
6. Adaptations

B. Physiological adaptations: takes shorter time

Changes in organisms metabolic processes (function)

antibiotic resistant bacteria

pesticide resistant insects (head lice)

herbicide resistant weeds

6 adaptations3
6. Adaptations

  • Not all features of an organisms are necessarily adaptive.

  • Example: helplessness of human babies.

  • Human babies are born at a much earlier stage of development than other mammals. This is probably not an adaptation but a consequence of the larger brains and upright posture of humans.

Chapter 15 evolution2

Chapter 15 Evolution

15-3 Shaping Evolutionary Theory

Population genetics and evolution
Population Genetics and Evolution

  • Darwin knew NOTHING about genes, never read the work of Mendel even though they lived about the same time

  • Darwin: 1809-1882

  • Mendel: 1822-1884

Populations not individuals evolve
Populations NOT individuals evolve

  • Individuals can’t change their genes, can’t change their genotypes and can’t change their phenotypes or trait

  • Individuals can only respond to their environments as their genes allow

Natural selection acts on phenotypes
Natural Selection acts on Phenotypes

  • If an individual has a phenotype that is poorly suited to their environment, the individual organism may not survive

  • and/or may not reproduce to pass their genes on to the next generation

Natural selection acts on phenotypes1
Natural Selection acts on Phenotypes

  • Each member of a population has the genes that characterize the traits of the species

  • All the genes (and alleles) of individuals make up the gene pool of the population

  • Evolution occurs as a population’s genes and their frequencies change over time

Allelic frequency
Allelic Frequency

  • Allelic frequency: % of any specific allele

    • = Number of specific allele

      Total number of alleles

  • Can change over time or stay the same

  • Hardy weinberg principle
    Hardy-Weinberg Principle

    • Hardy-Weinberg principlestates that when allelic frequencies remain constant, a population is in genetic equilibrium.

    Hardy weinberg principle1
    Hardy-Weinberg Principle

    • Equation: p2 + 2pq + q2 = 1

      and p + q = 1

    • This equation allows us to determine the equilibrium frequency of each genotype in the population.

    • Homozygous dominant (p2)

    • Heterozygous (2pq)

    • Homozygous recessive (q2)

    Genetic equilibrium
    Genetic Equilibrium

    • Frequency of alleles stays the same over many generations

    • Not evolving

    • Phenotypes remain the same too

    Changes in genetic equilibrium
    Changes in Genetic Equilibrium

    • Mutations

    • Genetic Drift

    • Gene Flow

    • Nonrandom mating

    • Natural Selection

    1 mutations
    1. Mutations

    • Caused by environmental factors like radiation and chemicals

    • Caused by random chance

    • Some mutations are lethal and quickly eliminated

    • Some mutations are helpful (useful) and new allele or gene becomes part of the population’s gene pool

    2 genetic drift
    2. Genetic Drift

    • Alteration of allelic frequency by chance events

    • Small populations that become isolated by natural events can evolve differently

    • Bottleneck effect: disasters such as earthquakes, floods kill victims unselectively

    • Founder effect: few individuals colonize an isolated area (Darwin’s finches)

    3 gene flow
    3. Gene Flow

    • Movement of individuals into or out of a population

    • When individuals immigrate or emigrate their genes go with them

    • Example: westward expansion in the US

    4 nonrandom mating
    4. Nonrandom mating

    • Usually organism mate with those in close proximity. (May result in inbreeding).

    • Usually organisms mate with those of the same or similar phenotype.

    5 natural selection
    5. Natural Selection

    • Acts on variation

    • Some variations increase or decrease an organism’s chance for survival

    • Variation can be inherited and are controlled by alleles

    5 natural selection1
    5. Natural Selection

    • Four Types of Natural Selection that act on variation

      • Stabilizing Selection

      • Directional Selection

      • Disruptive Selection

      • Sexual Selection

    Stabilizing selection
    Stabilizing Selection

    • Favors average

    • Reduces variation

    • Example: Large spiders easy to see and be eaten while small spiders have a hard time getting food

    Directional selection
    Directional Selection

    • Favors one extreme

    • Can lead to rapid evolution

    • Example: Over time there were more and more darker colored Peppered Moths in the industrial area of England in the 1800’s

    Disruptive selection
    Disruptive Selection

    • Both extremes are favored

    • Average (mean) disfavored

    • Leads to the evolution of two species

    • Example: Light yellow butterfly overtime becomes either nearly white or orange

    Sexual selection
    Sexual Selection

    • Sexual selection operates in populations where males and females differ significantly in appearance.

    • Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival.

    • Example: tail of mail peacocks, while beautiful, makes the organism a greater target for predators.

    The evolution of species
    The Evolution of Species

    • Species: group of organisms that look alike and can breed to produce fertile offspring

    • Speciation: process of evolution of new species

      • occurs when members of similar populations no longer interbreed to produce fertile offspring in their natural environment

    Reproductive isolation
    Reproductive Isolation

    • Prezygotic isolation mechanisms make fertilization unlikely.

    • Can’t mate to produce fertile offspring

    • Genetic differences: genetic material too different so no fertilization results

    • Behavioral differences: mate at different times of day or at different season; different “courting” rituals

    Reproductive isolation1
    Reproductive Isolation

    • Postzygotic isolation occurs when fertilization has occurred but a hybrid offspring cannot develop or reproduce.

    • Prevents offspring survival or reproduction.

    Fertilization is possible between a tiger and a lion but the offspring is sterile.


    • In allopatric speciation a physical barrier divides one population into two or more populations; geographic isolation.

    Geographic isolation
    Geographic Isolation

    • Islands, lava flows, rock slides, rivers changing course

    • Populations become physically separated

    • Over time each small population adapt differently to environments and have different gene pool

    • When gene pool becomes too different then two species exist


    • In sympatric speciation a species evolves into a new species without a physical barrier.

    Patterns of evolution
    Patterns of Evolution

    • Divergent Evolution (adaptive radiation): become different

    • Convergent Evolution: become the same

    • Coevolution: the evolution of one species effects the evolution of another species

    Divergent evolution
    Divergent Evolution

    • Adaptative radiation:: one ancestral species evolves into many species to fit diverse habitats

    Convergent evolution
    Convergent Evolution

    • Distantly related organisms evolve similar traits

    • Occurs when unrelated species occupy similar environments in different parts of the world

    • African and American cactus


    • The relationship between two species might be so close that the evolution of one species affects the evolution of the other species.

    • Example: specialized mouth parts

    Two theories of speciation
    Two Theories of Speciation

    • Gradualism: species originate through gradual, slow change

      • Evolution of the horse

    Two theories of speciation1
    Two Theories of Speciation

    • Punctuated Equilibrium: speciation relatively quickly (10, 000 years) with long periods of no evolution (genetic equilibrium)

    • High environmental change

      • Evolution of elephants