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Unit 8 Evolution
What is Evolution?
A well-supported scientific theory stating that organisms change over time
Evidence in stone
Preserved remains of a once living organism is called a FOSSIL
Fossil evidence supported that organisms changed gradually
Anatomical Evidence
Comparative Anatomy: study of similarities and differences between organismsHomologous StructuresAnalogous StructuresVestigial Organs
Homologous StructuresAs similar organisms adapted to different environments,
the function of their appendages changed. Result of descent with modification from a common ancestor.
A bird’s arms became wings to flap
A human’s arm is used to pick-up, carry, grasp, etc…
A horse’s arm became a fore-leg to run on
Analogous Structures
Different organisms began living in similar environments - their appendages evolved to perform the same function, although structurally different.
A butterfly has wings to fly that are made from an exoskeleton
A sparrow has wings to fly that have an endoskeleton
BirdButterfly
Vestigial Structures
Structures which remain in organisms but have no obvious function Leg bones in snakes and whales Appendix in humans ** Ear muscles in humans
Comparative Embryology
Examining the embryos of organisms
Organisms with similar embryos are thought to be more closely related
Biochemical Evidence (Molecular Biology)
Comparison of the amino acid sequencesChimp and human hemoglobin are VERY similar
Genetic Evidence
DNA passes on traits When mutations occur the genes and
chromosomes can changeHumans have imposed change
through selective breedingThe higher the percentage of
similarities the closer the relationship between two organisms
Jean Baptiste de Lamark
First to recognize that organisms change
Published his hypotheses in 1809
Theory was disproved!
3 Key Assumptions:Desire to Change: organisms have an
inborn urge to better themselvesLaw of Use and Disuse: body parts
that are used will develop; those not used will become smaller/disappear
Inheritance of Acquired Characteristics: organisms pass on traits acquired during their lifetime
Jean Baptiste de Lamark
Lamark’s Giraffes
Charles Darwin
Credited for the theory of evolutionHMS Beagle sailed in 1831 – Galapagos
IslandsPublished Origin of Species in 1858
Darwin’s Observations
Observed tortoises, iguanas, and finches
The islands had different climates and vegetation
The animals were similar… but had noticeable differences…why?
Species vary globallySpecies vary locallySpecies vary over
time
Darwin’s Theory of Natural Selection
Variations help members of a species to survive in a given environment
The environment selects the beneficial adaptation and over time this trait will become more prevelant
Darwin’s Assumptions Variations
Differences among members of the same speciesOverproduction
More offspring are produced than will surviveStruggle for Existence
Predation and competitionSurvival of the Fittest (Natural
Selection) Individuals best suited for the environment will
survive, reproduce, and pass on traits to their offspring
Descent with ModificationPrinciple that species change but descend from
common ancestors
Darwin’s Finches
Fossil Formation
Dead organisms are buried by layers of sediment, which forms new rock
The preserved remains may later be discovered and studied.
Water carries small rock particles to lakes and seas
Fossil Record
Preserved remains of a once living organism is called a FOSSIL IE: amber, sedimentary rock, tar, and ice
Fossil record is incomplete
Relative Dating
Used to ESTIMATE the age of fossils
Older fossils are in deeper layers of rock
Patterns and Processes of Evolution
Macroevolutionary Patterns Large-scale (more than a single species) Occurs over long periods of time
Microevolution Small-scale (within a single species) Forms variations in populations
22
Speciation – Isolating MechanismSpecies – group of organisms that interbreed to
produce fertile offspring under normal conditions –
share a common gene poolSpeciation – formation of a new species
Requires reproductive isolation – organisms do not interbreed; gene pools become separateBehavioralGeographicTemporal
23
Patterns of Extinction
Background Extinction – “business as usual” extinction – slow and steady
Mass Extinction – many species become extinct over a short period of timeCauses:AsteroidVolcanic eruptionsMoving continentsChanging sea levels
24
Rates of Evolution
Gradualism – change in species is slow and steady
Punctuated Equilibrium – long periods of stability followed by short periods of rapid change
25
Patterns of Macroevolution:
Adaptive RadiationA single species evolves into many speciesOften occurs when a niche opens up
26
Organisms come to resemble one another but evolved differently
Source of analogous structures!
Examples: Dolphins and sharks Marsupials and
mammals
Patterns of Macroevolution:
Convergent Evolution
27
Coevolution
Organisms with close ecological relationships evolve togetherPollinators and flowers
28
The Role of Genes in Evolution
In terms of genetics, evolution is the change in the frequency of alleles in a population’s gene pool
Natural selection leads to that change
29
Genetic DriftRandom change in allele frequency –
changes in the gene pool of a small population due to chance
Types of Genetic Drift: Bottleneck Effect – change in allele
frequency following dramatic reduction in population size
30
Genetic Drift Founder Effect – small group colonizes a
new habitat
31
Molecular Evolution
Molecular Clocks – use mutation rates in DNA to estimate time two species have been evolving independently
32
Molecular Evolution: Hox Genes
33
Genes which control an organism’s basic body plan Anterior/posterior ends Limbs, wings
small sequence changes during embryological development can cause large changes in adults
Ancient Earth
Atmosphere was composed of gases:
CO2, N2, water vapor, CH4, H2S
No O2
Earth formed ~4.6 billion years ago
First Organic Molecules
1950’s Miller & Urey reproduced conditions of ancient Earth
Electric sparks simulated lightning
Amino acids began to form
First Cell
Oxygen Accumulation in Atmosphere
What is a Primate?Binocular VisionDeveloped brainLong fingers & toesRotating shoulders
What makes us Human?
Characteristics of the Hominine Family Bipedal Opposable
Thumbs Larger Brains
Did we evolve from chimps?
Hominine Evolution
Ardipithecus ramedus “Ardi”, 4.4 myaAustralopithecus afarensis “Lucy”, 3.2 myaHomo habilis “handy man”, ≈ 2 mya
Used tools, first of the genus Homo
Homo erectus, “Java Man”, ≈ 1.6 mya 1st to use fire
Homo neanderthalensis ≈ 200,000 years ago
Homo sapien Modern Human ≈ 100,000 years ago
Family Tree or Bush?