Evolution The theory that organisms have changed gradually over time.
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Transcript of Evolution The theory that organisms have changed gradually over time.
Evidence to support the Theory of Evolution
• Fossil Record - Law of Superposition• Comparative Anatomy:
– Homologous Structures– Analogous Body Structures– Vestigial Body Structures
• Comparative Embryology• Comparative Biochemistry (genes/proteins) • Direct Observation
Fossil Record
• Evidence of change over time
• Relative age of extinct organisms
• Age of the Earth
Fossil Evidence:• Once living
remains of organisms
• Limited:
1. Type of material preserved (bone, shell, impressions, amber)
2. Incomplete record
3. Easily disrupted
1. Homologous Structures – Parts on different organisms that are similar in structure (and sometimes function) and seem to indicate common origin – common ancestor.
Indicate divergent evolution – things becoming more different.
• 2. Analogous Structures – similar in function and appearance, but not in origin. – Illustrate convergent evolution – things becoming more
similar.
Fly wing
Bird Wing
Comparative Embryology
• shows early developmental stages in embryos of different vertebrate species is very similar
• Inherited same basic body plan from a common ancestor
• Become distinct at later stages
Genetic Evidence
• Each new generation of organisms in a population shows some change or variation as a result of:– Mutations– Meiosis & fertilization
Comparative Biochemistry
Similar organic compounds (proteins, etc.)
Humans and chimp DNA – 98% similar
Humans and other mammals – 80% similar
Direct Observation
Rapid evolution1. Antibiotic resistant bacteria
2. Resistance of insects to pesticides
3. HIV strains
How does evolution occur?Lamarckism vs. Darwinism
• Jean Baptist Lamarck (1744 – 1829)– “Acquired Characteristics” develop and are
passed on to offspring.– Experimentation failed to support Lamarckism
Influences on Darwin
• 1. Worked as naturalist on HMS Beagle for 5 year voyage– Collected fossils and specimens– Noted tremendous biodiversity– Galapagos organisms unique yet similar to
species elsewhere– Formulated his idea of “Descent with
Modification” (changes occur from one group of descendants to the next)
2. Studied Charles Lyell – Geologist who said,
“The present is the key to the past.” The same forces acting on earth in the past are
continuing today.
3. Studied work of Thomas Malthus - 1798
• Human population growing faster than food supply - creates competition• Darwin extended idea to other organisms.
6. Noted Artificial Selection
• Farmers and breeders practice selective breeding to produce preferred offspring.
Adaptations are physical or behavioral traits that make an organism better able to survive
in its environment.
Tartan Hawkfish
Cryptic Frog
Walking Stick
www.howstuffworks.com
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Sea Dragonwww.liverpoolmuseum.org/uk
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“On the Origin of Species by Means of Natural Selection”
published in 1859• Summary of Theory of Natural Selection:
1. Overproduction of Offspring (more produced than can survive)
2. Variation within a population
3. Struggle to survive creating competition
4. Successful reproduction - Individuals with better adaptations pass these on to offspring (survival of the fittest)
Sources of Variation
• S – sexual reproduction
• C – crossing over during meiosis
• A – assortment of alleles during meiosis
• M - mutations
Pepper Moths - England
• Original color – 99% white (white bark on trees)
• Industrial Revolution, 1850s – produced smog
• Environment changes - 1890s - 99% black (dark bark on trees)
Which trait was a better adaptation and so selected for?
How did this affect the frequencies of the different alleles?
Gene Pools
Population Genetics
• Natural Selection acts on individuals, BUT
populations evolve
• An individual’s genotype remains constant
• A population’s gene pool (entire collection of genes in a population) evolves as allele frequencies change due to natural selection
History of Earth
• Earth is @ 4.6 billion years old –
• Early earth – – hostile environment – volcanoes, lightning,
meteorites, UV light
– Primitive atmosphere: CH4, NH3, H2, H2O,
• All elements for life present – but no pure oxygen
Origin of Life
Primordial soup hypothesis: Primitive atmosphere filled with carbon, hydrogen, nitrogen, water vapor - bombarded by lightning and uv radiation, producing organic compounds and precursors to first cells, which ended up in oceans
• Stanley Miller’s Experiment1953 – University of Chicago
• After 1 week simple organic compounds including amino acids were present
Origins of Life: Oceans as Nursery Simple compounds
Complex compounds
Primitive precells
Prokaryotes