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Evidence for Evolution by Natural Selection
Hunting for evolution clues… Elementary, my dear, Darwin!
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Evidence supporting evolution
Fossil record shows change over time Anatomical record comparing body structures homology & vestigial structures embryology & development Molecular record comparing protein & DNA sequences Artificial selection human caused evolution
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1. Fossil record Layers of rock contain fossils
new layers cover older ones creates a record over time fossils show a series of organisms have lived on Earth over a long period of time
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Life on Earth has changed
Fossils tell a story… the Earth is old Life is old Life on Earth has changed
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Evolution of birds Today’s organisms descended from ancestral species
Fossil of Archaeopteryx lived about 150 mya links reptiles & birds The avian nature of the brain and inner ear of Archaeopteryx (Alonso et al. 2004) - Archaeopteryx, the earliest known flying bird from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. Alonso et al. (2004) investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. A reconstruction of the braincase and endocasts of the brain and inner ear suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. Alonso et al. (2004) concluded that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability.
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We found the fossil — no joke!
Land Mammal ? Complete series of transitional fossils ? Where are the intermediate fossils? ? ? There are innumerable intermediate & transitional forms Whales as land creatures returning to the water…. Where are the intermediate forms of whale ancestors? Cartoon making fun of this idea. The cartoons disappeared years ago when this fossil was found. Ambilocetic natans = “Walking whale who likes to swim” 4-5 intermediate forms all found in last 2 decades Indus River valley in between India & Pakistan. Someone’s idea of a joke! Ocean Mammal But the joke’s on them!!
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Evolution from sea to land
2006 fossil discovery of early tetrapod 4 limbs Missing link from sea to land animals
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3. Anatomical record Animals with different structures on the surface
But when you look under the skin… It tells an evolutionary story of common ancestors
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How could these very different animals have the same bones?
Compare the bones The same bones under the skin limbs that perform different functions are built from the same bones How could these very different animals have the same bones?
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Homologous structures
Structures that come from the same origin homo- = same -logous = information Forelimbs of human, cats, whales, & bats same structure on the inside same development in embryo different functions on the outside evidence of common ancestor
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But don’t be fooled by these…
Analogous structures look similar on the outside same function different structure & development on the inside different origin no evolutionary relationship How is a bird like a bug? Solving a similar problem with a similar solution
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Analogous structures Dolphins: aquatic mammal Fish: aquatic vertebrate
both adapted to life in the sea not closely related Watch the tail!
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They just came up with the same answer!
Flight evolved 3 separate times — evolving similar solutions to similar “problems” Convergent evolution 3 groups with wings Does this mean they have a recent common ancestor? They just came up with the same answer! NO!
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Convergent evolution led to mimicry
Why do these pairs look so similar? Monarch male poisonous Viceroy male edible Which is the moth vs. the bee? Which is the fly vs. the bee? fly bee moth bee
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Because they used to walk on land!
Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures? Because they used to walk on land!
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Comparative embryology
Development of embryo tells an evolutionary story similar structures during development all vertebrate embryos have a “gill pouch” at one stage of development
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3. Molecular record Comparing DNA & protein structure
everyone uses the same genetic code! DNA 10 20 30 40 50 60 70 80 90 100 110 120 Lamprey Frog Bird Dog Macaque Human 32 8 45 67 125 compare common genes compare common proteins number of amino acids different from human hemoglobin
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Building “family” trees
Closely related species are branches on the tree — coming from a common ancestor
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“descendants” of wild mustard
4. Artificial selection How do we know natural selection can change a population? we can recreate a similar process “evolution by human selection” “descendants” of wild mustard
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“descendants” of the wolf
Selective Breeding Humans create the change over time “descendants” of the wolf
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I liked breeding pigeons!
Artificial Selection …and the examples keep coming! I liked breeding pigeons!
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Artificial Selection gone bad!
Unexpected consequences of artificial selection Pesticide resistance Antibiotic resistance
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Insecticide resistance
Spray the field, but… insecticide didn’t kill all individuals variation resistant survivors reproduce resistance is inherited insecticide becomes less & less effective The evolution of resistance to insecticides in hundreds of insect species is a classic example of natural selection in action. The results of application of new insecticide are typically encouraging, killing 99% of the insects. However, the effectiveness of the insecticide becomes less effective in subsequent applications. The few survivors from the early applications of the insecticide are those insects with genes that enable them to resist the chemical attack. Only these resistant individuals reproduce, passing on their resistance to their offspring. In each generation the % of insecticide-resistant individuals increases.
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Any Questions??
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Natural Selection of Strawfish
How does natural selection affect genes? How do genes affect evolution?
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1. No Predator Preferences
FISH ALLELES blue green yellow Gen. 1 25% 50% Gen. 4 27% 55% 18% 45% No selection force in one specific direction. No clear pattern of change.
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2. Predator Prefers BLUE 25% 50% 13% 37% 38% 62%
FISH ALLELES blue green yellow Gen. 1 25% 50% Gen. 4 13% 37% 38% 62% Selection against blue. Fewer blue fish and fewer blue alleles.
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3. Predator Prefers GREEN
FISH ALLELES blue green yellow Gen. 1 25% 50% Gen. 4 36% 28% Selection against green. Fewer green fish but same variation in alleles.
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4. GREEN is Camouflaged 25% 50% 20% 60%
FISH ALLELES blue green yellow Gen. 1 25% 50% Gen. 4 20% 60% Selection against blue & yellow. More green fish but same variation in alleles.
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Australian Marsupials
Parallel Evolution Niche Placental Mammals Australian Marsupials Burrower Mole Anteater Mouse Lemur Flying squirrel Ocelot Wolf Tasmanian “wolf” Tasmanian cat Sugar glider Spotted cuscus Numbat Marsupial mole Marsupial mouse Nocturnal insectivore Climber Glider Stalking predator Chasing not closely related marsupial mammal placental filling similar roles in nature, so have similar adaptations
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Vestigial organs Structures on modern animals that have no function
remains of structures that were functional in ancestors evidence of change over time some snakes & whales have pelvis bones & leg bones of walking ancestors eyes on blind cave fish human tail bone
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