EvolutionEvolution

• Darwin’s Theory of EvolutionDarwin’s Theory of Evolution•Evolution of PopulationsEvolution of Populations

•The History of LifeThe History of Life•ClassificationClassification

• Evolution =– “Change over time”– The process by which modern organisms

have descended from ancient organisms– A verb!!! NOT a noun!!!

• Theory =– A well-supported testable explanation of

phenomena that have occurred in the natural world

– Based on measurable observations of the natural world

• Microevolution –– Describes the details of how populations

change from generation to generation– Describes how new species originate

• Macroevolution –– Describes patterns of changes in groups of

related species over broad periods of geologic time

– Determines the phylogeny (evolutionary relationships) among species/groups of species

Darwin’s Theory of Darwin’s Theory of EvolutionEvolution

Voyage of the H.M.S.Voyage of the H.M.S. Beagle Beagle (1831-1836)(1831-1836)

• As Darwin made observations on his journey he wondered about…– Why were many plants and animals well suited to the

habitat in which they were found?– Puzzled by where plants and animals lived and did

not live.– Were fossils related to species still around today?– Darwin was also intrigued by the tortoise diversity on

the Galapagos Islands.

Ideas that shaped Darwin’s Ideas that shaped Darwin’s ThinkingThinking

• Hutton’s theory of Geologic Change (1785) – – Earth is shaped by geological forces that took

place over extremely long periods of time– Earth is millions of years old (not thousands)

• Thomas Malthus (1798) –– Predicted that the human population will grow

faster than the space and food supplies needed to sustain it

Ideas that shaped Darwin’s Ideas that shaped Darwin’s ThinkingThinking

• Jean-Baptiste Lamarck (1809)–– 1st to propose a theory of how organisms change over

time (Use and disuse, Inheritance of acquired traits, tendency toward perfection)

– Incorrect theory an organism’s behavior has no effect on heritable characteristics!!!

• Lyell’s Principles of Geology (1833) –– Processes occurring now have shaped

Earth’s geological features over long periods of time.

On the Origin of Species On the Origin of Species

• Darwin did not rush to publish (waited 25 years!)

• Published his work because of Alfred Wallace (who had similar theories)

• 1859 – On the Origin of Species

• Caused a controversy because the theory radically challenged church doctrine

Evolution by Natural SelectionEvolution by Natural Selection

• Struggle for Existence –– Members of each species compete to obtain food,

living space, and other resources necessary for life

• Survival of the Fittest –– Individuals that are better suited to their environment

survive and reproduce most successfully.– Fitness ability to survive and reproduce– Adaptation any inherited characteristic that

increases an organism’s chance at survival

Evolution by Natural SelectionEvolution by Natural Selection• Descent with Modification –

– Species today look different from their ancestors

– Natural selection produces organisms that have:

• Different structures• Establish different niches• Occupy different habitats

– All living organisms are related to one another

Evidence of EvolutionEvidence of Evolution

• Evidence includes:– The fossil record – Geographic distribution – Homologous and Analogous structures – Similarities in Embryology– Similarities in Biochemistry(review the activities done for each of

these)

Evolution of PopulationsEvolution of Populations

Genetics and the EnvironmentGenetics and the Environment

• The characteristics of organisms not solely determined by inherited genes– Determined by interaction between genes and

the environment– Genes provide a plan for development how

the plan unfolds also depends on the environment

Genes and VariationGenes and Variation

• 2 main sources of genetic variation:– Mutations– Gene shuffling during sexual reproduction

• Gene pool all genes (and alleles) that are present in a population

• Relative frequency # of times an allele occurs in a gene pool (given as a percentage)

• Evolution is any change in the relative frequency of alleles in a population

Natural Selection and EvolutionNatural Selection and Evolution

• Natural Selection never acts directly on genes– Works on the entire organism…can only affect

which individuals survive and reproduce– If an individual dies does not pass on

genes– ALSO…Individuals do not evolve…

Populations evolve as the gene pool changes because of the relative frequency of the alleles changes

Natural Selection and Genetic Natural Selection and Genetic ChangeChange

• Single-Gene traits leads to changes in allele frequencies (thus to evolution)

• Natural Selection on Polygenic Traits leads to changes in the distribution of phenotypes (3 ways):– Directional Selection– Stabilizing Selection– Disruptive Selection

Directional SelectionDirectional Selection

Stabilizing SelectionStabilizing Selection

Disruptive SelectionDisruptive Selection

How do Populations Evolve?How do Populations Evolve?

• Natural Selection in not the only source of evolutionary change

• Genetic drift – Individuals that carry a particular allele may leave

more descendents BY CHANCE.– Over time, a series of chance occurrences can cause

an allele to become common in a population– A new species can result if there is enough of a

genetic difference between the original population and the new population

Evolution vs. Genetic EquilibriumEvolution vs. Genetic Equilibrium

• Hardy-Weinburg Principle allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change– Constant allele frequencies = genetic

equilibrium

Hardy-WeinburgHardy-Weinburg

• In order to maintain genetic equilibrium there are several conditions that must be met:– Random mating– Large population– No movement into or out of the population– No mutations– No Natural Selection

• Refer to the activity for review

The Process of SpeciationThe Process of Speciation

• Formation of a new species (organisms that breed and produce fertile offspring)

• As new species evolve, populations become isolated from one another– Reproductive isolation members of 2

populations can no longer interbreed and produce fertile offspring

Isolating MechanismsIsolating Mechanisms

• Behavioral Isolation differences in courtship or other reproductive strategies that involve behavior

• Geographic Isolation 2 populations are separated by geographic barriers

• Temporal Isolation 2 or more populations reproduce at different times of the year

Case Study: Darwin’s finchesCase Study: Darwin’s finches

• Evolution of Darwin’s finches – Founders arrive– Separation of populations– Changes in the gene pool– Reproductive Isolation– Ecological Competition– Continues Evolution

Patterns of EvolutionPatterns of Evolution

• 4 main patterns – Divergent Evolution: 2 or more species originate from

a common ancestor– Convergent Evolution: 2 unrelated species that share

similar traits (independent adaptation to the environment)

– Parallel evolution: 2 related species (lineages) that have made similar changes after the common ancestor

– Coevolution: evolution of one species in response to new adaptations in another (predator/prey relationship)

Divergent EvolutionDivergent Evolution

Convergent EvolutionConvergent Evolution

Parallel evolutionParallel evolution

CoevolutionCoevolution

MacroevolutionMacroevolution

• 2 distinct theories:– Gradualism

• Evolution occurs by the gradual accumulation of small changes

– Punctuated Equilibrium• Evolutionary history consists of geologically long

periods of stasis with little or no evolution, interrupted by geologically short periods of rapid evolution

GradualismGradualism

Punctuated EquilibriumPunctuated Equilibrium

The Origin of Life: Chemical The Origin of Life: Chemical EvolutionEvolution

• The following is a hypothesized order of events that led to life on Earth:

1. The Earth and its atmosphere formed– Outgassing of the molten interior (CO, CO2, H2,

N2, H2O, S, HCl, HCN)

2. The primordial seas formed

3. Complex molecules were synthesized– Oparin/Haldane and Miller experiments

Life on Earth (continued)Life on Earth (continued)

4. Polymers and self-replicating molecules were synthesized

5. Organic molecules were concentrated and isolated into protobionts

6. Primitive heterotrophic prokaryotes formed

7. Primitive autotrophic prokaryotes were formed

Life on Earth (continued)Life on Earth (continued)

8. Oxygen and the ozone layer formed and abiotic chemical evolution ended

9. Eukaryotes formed (“endosymbiotic theory”)

• Originated from a mutually beneficial association among various kinds of prokaryotes• Mitochondia, chloroplasts possess their own

DNA, reproduce independently of the cell, resembles bacteria and cyanobacteria

Standard ClassificationStandard Classification

• Developed by Carolus Linnaeus in the 18th century

• Organizes organisms into groups and subgroups based on evolutionary relationships

• Often revised when new relationships are discovered (DNA evidence)– Example: Pseudocalanus spp.

Classification levels:Classification levels:

• Kingdom (broad)

• Phylum

• Class

• Order

• Family

• Genus

• Species (specific)