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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
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)
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
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)
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
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.