objective: understand how the mechanism of natural selection causes evolution
TRANSCRIPT
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Objective:Understand how the mechanism of natural
selection causes evolution.
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Bible: Earth is only a few thousand years old.
Aristotle: organisms don’t change◦ Scala naturae: ladder of
increasing complexity Linnaeus: taxonomy
(naming/classifying organisms) using genus and species
Cuvier: paleontologist discovered the deeper (older) the rock, the less like modern organisms fossils look.◦ Also found extinctions and
speciations.
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Gradualism (slow, continuous change) Hutton: geologic features explained by graddual
erosion and deposition. Lyell: uniformitarianism – same geologic
processes are operating today as in the past, at the same rate.◦ Darwin proposed this also happened with organisms.
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Lamarck (INCORRECT) Use and disuse: body parts used got
bigger/stronger; not used got small/disappeared.
These body parts could be passed on to offspring (inheritance of acquired characteristics).
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Darwin’s Research From 1831-6 Charles Darwin traveled the
world on the HMS Beagle. Earthquakes moved rocks up Andes
mountains exposing sea creature fossils. Finches were unique to islands but also
were found on 2 or more.◦ They came from S. America and diversified
according to food found on the island they were on.
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Published in 1859 stating:1. All organisms come from ancestors2. Mechanism for evolution is natural selection Populations change over generations passing beneficial
heritable traits to offspring.
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Modifications (adaptations) that helped organisms survive and have more offspring with these modifications (descent).
Evolutionary trees could be made showing where fossils fit in with living organisms.
Hyracoidea(Hyraxes)
Sirenia(Manatees
and relatives)
Yea
rs a
goM
illio
ns
of y
ea
rs a
go Deinotherium
Mammut
Stegodon
Mammuthus
Platybelodon
Barytherium
Moeritherium
Elephasmaximus
(Asia)
Loxodontaafricana(Africa)
Loxodontacyclotis(Africa)
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How natural selection works: Struggle for existence. Individuals survive due to heritable
phenotypic differences. These lead to changes in characteristics of
a population over generations.
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Artificial Selection Humans change organisms by choosing
traits and breeding. Led Darwin to believe that natural selection
could work the same over longer periods of time thus produces drastic changes.
Terminalbud
Lateralbuds
Brussels sproutsCabbage
Flowercluster
Leaves
Cauliflower
Flowerandstems
Broccoli Wild mustard Kohlrabi
Stem
Kale
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Summary of Natural Selection Individuals do not change. Only works on heritable traits. The same trait is not always favorable.
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Guppies Size and age differences between
populations Different predators
◦ Killifish: preys on juveniles◦ Pike-cichlid: preys on mature
Result: sexual maturity in pops with killifish decreased.
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Drug Resistant Bacteria◦ Staphylococcus aureus is commonly found on
people◦ Became resistant to:
penicillin in 1945 (2 years after it was 1st widely used) methicillin in 1961 (2years after it was 1st widely used)
◦ Methicillin inhibits a protein in bacteria’s cell walls MRSA uses a different protein and is now pathogenic.
◦ MRSAs are now resistant to many antibiotics12,750,000
2,500,000
2,250,000
2,000,000
1,750,000
1,500,0001,250,000
1,000,000
750,000
500,000
250,000 base pairs
Chromosome map of S. aureus clone USA300
Key to adaptations
Methicillin resistanceAbility to colonize hosts
Increased disease severityIncreased gene exchange(within species) andtoxin production
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Evidence for Evolution• Homology: similarities resulting from common ancestry
– Comparative Anatomy– Homologous: same structure different function– Vestigial: remains of structures that have no current
function– Molecular: same DNA/RNA/amino acids
Human Cat Whale Bat
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Homologies◦ Comparative embryology reveals anatomical
homologies not visible in adult organisms
◦ Homologies form nested patterns in evolutionary trees
◦ Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data
Pharyngealpouches
Post-analtail
Chick embryo (LM) Human embryo
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Convergent Evolution◦ The evolution of similar (analogous) features in
distantly related groups Analogous traits arise when groups independently
adapt to similar environments in similar ways◦ Convergent evolution does not provide
information about ancestry
Sugarglider
Flyingsquirrel
NORTHAMERICA
AUSTRALIA
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The Fossil Record◦ The fossil record provides evidence of the extinction
of species, the origin of new groups, and changes within groups over time
◦ Fossils can document important transitions◦ EX: the transition from land to sea in the ancestors of
cetaceans
Other even-toedungulatesHippopotamuses
†Pakicetus
†Rodhocetus
†Dorudon
Livingcetaceans
Commonancestorof cetaceans
Millions of years ago70 Key60 50 40 30 20 10 0 Pelvis Tibia
Femur Foot
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Biogeography: closely related species are geographically close.◦ Earth’s continents were formerly united in a
single large continent called Pangaea, but have since separated by continental drift
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Study of molecular basis of genes and gene expression
Universality of genetic code
Conservation of amino acid sequences in proteins such as hemoglobin