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Natural Selection
evolution.berkeley.edu/evosite/misconceps
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*Charles Darwin (1809-1882)
Naturalist aboard HMS Beagle Collected living specimens & fossils Visited Galapagos Islands (p.394, fig. 15.1)
Tortoises Finches Marine iguanas
Bred pigeons – artificial selection
http://nayagam.files.wordpress.com/2006/02/397px-Charles_Darwin_by_G._Richmond.jpg
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**Darwin cont. From collections & observations
Natural selection Mechanism for change in populations Organisms with favorable variations survive,
reproduce, & pass variations on to next generation
Published On the Origin of Species by Means of Natural Selection
http://uk.gizmodo.com/charles_darwin_l.jpg
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Mechanisms of Evolution Populations evolve, NOT individuals Gene pool - all alleles in a population’s genes
together (remember: alleles: alternative forms of a gene)
Allelic frequency - % of any specific allele (p.405 snapdragons)
Genetic equilibrium - frequency of alleles remains same over generations = no evolution
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How does evolution happen? - disrupting genetic equilibrium Mutations - caused by radiation or chemicals Genetic drift - alteration of allelic frequencies by
chance events (random, affects small populations greater)
Gene flow - Migration & Emigration Natural selection - allelic frequencies change
due to nature selecting for advantageous variations Stabilizing, directional, and disruptive
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Stabilizing selection - favors average phenotypes
Spiders- larger spiders
eaten by predators
-Smaller spiders can’t
catch enough food
-Favors average size
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Directional selection - favors one extreme (on graph, selects to left or right)
Woodpeckers-
longer beaks
eat more insects
buried deep in bark
(have more fitness)
Long beaks favored Can lead to
rapid evolution
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Disruptive selection - eliminates intermediate phenotypes
In an environment,
medium-sized seeds
become less common
-Birds with smaller or
larger beaks have easier
time finding food
= higher fitness
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How do changes in gene pool lead to evolution? Speciation - when members of similar populations no
longer interbreed to produce fertile offspring within natural environment
Geographic isolation - physical barrier divides a population Lava from volcanic eruptions, sea-level changes, rivers,
mountains Reproductive isolation - populations no longer mate and
produce fertile offspring Behavorial - different mating calls or seasons Different genetic material Polyploidy - having multiple chromosome sets
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Speciation rates - 2 hypotheses, both supported by fossil record Gradualism - species originate through
gradual change of adaptations; slow & steady
Punctuated equilibrium - species originate quickly, in rapid bursts
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Patterns of evolution Divergent evolution - occurs when populations
change as they adapt to different environmental conditions Adaptive radiation - ancestral species evolves into
many new species to fit various niches Hawaiiian honeycreepers; Darwin’s finches
Convergent evolution - unrelated species evolve similar traits because of similar environmental pressures Different cactus species around the world
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*Adaptations: Evidence for Evolution Structural adaptations
Body parts of an organism that help it survive Ex. Teeth, claws, keen eyes, thorns,
Mimicry – more subtle One harmless species looks a dangerous one
Harmless fly looks like a wasp; scarlet kingsnake looks like coral snake
Two or more harmful species look alike Yellow jackets, honeybees, many wasps use same coloring to
say “Hey, stay away, I’ll hurt you!”
Camouflage – enables species to blend in
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www.nature.com/.../n7023/images/433205a-f1
Photo Credit: Dan Hipes
http://www.outdooralabama.com/watchable%2Dwildlife/what/Reptiles/Snakes/scarlet.cfm
Photo Credit: AZ Herpetological Associationhttp://www.sloanmonster.com/images/coral.jpg
farm1.static.flickr.com/144/383488615_b937af4
lh3.google.ca/abramsv
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Can you think of an example for camouflage?
I’ll show you some
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*Physiological adaptations Can happen very quickly Changes in an organism’s metabolic
processes Antibiotic-resistance bacteria
Penicillin not as effective now Insects & weeds resistant to pesticides
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Strains of drug-resistant TB
Articles on: -Antibiotic resistance -Crop pest evolutionMRSA podcast
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*Indirect evidence for evolution Fossils
Assembling a puzzle without all the pieces What percentage of “Lucy” did they find?
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Anatomy (p. 401 fig. 15.6) Homologous structures
Structural features with common evolutionary origin
*Indirect evidence for evolution
http://evolution.berkeley.edu/evosite/lines/IIhomologies.shtml
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*Anatomy cont. Analogous structures
Body parts have similar function but not common ancestry Bird wing, butterfly wing
Vestigial structures Body part in present-day organism that no longer
serves its original purpose (but was useful at some time)
Our wisdom teeth, appendix, blind cave fish with eyes
http://evolution.berkeley.edu/evolibrary/article//evo_31
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*Indirect Evidence for Evolution Embryology
Embryo – earliest stage of growth & development of plants & animals
Page 402 fig. 15.9: You had a tail and gills?? Biochemistry
Biochemical molecules: RNA, DNA, ATP, and many enzymes Compare amino acid sequences among organisms Enzyme - cytochrome c - involved in cellular respiration
P.403