Natural Selection

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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-C
harles_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 populations 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 cant
• 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 Darwins 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, Ill hurt you!
• Camouflage enables species to blend in

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lh3.google.ca/abramsv
www.nature.com/.../n7023/images/433205a-f1
farm1.static.flickr.com/144/383488615_b937af4
Photo Credit AZ Herpetological
Associationhttp//www.sloanmonster.com/images/cor
al.jpg
Photo Credit Dan Hipeshttp//www.outdooralabama.
com/watchable2Dwildlife/what/Reptiles/Snakes/scar
let.cfm
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• Can you think of an example for camouflage?
• Ill show you some

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Physiological adaptations

• Can happen very quickly
• Changes in an organisms metabolic processes
• Antibiotic-resistance bacteria
• Penicillin not as effective now
• Insects weeds resistant to pesticides

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Articles on -Antibiotic resistance
-Crop pest evolution MRSA podcast
Strains of drug-resistant TB
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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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Indirect evidence for evolution

• Anatomy (p. 401 fig. 15.6)
• Homologous structures
• Structural features with common evolutionary
  origin

http//evolution.berkeley.edu/evosite/lines/IIhomo
logies.shtml
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Anatomy cont.
http//evolution.berkeley.edu/evolibrary/article//
evo_31

• 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

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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