1. Natural Selection
evolution.berkeley.edu/evosite/misconceps

2. *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

3. **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

4. 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

5. 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

6. Stabilizing selection - favors average phenotypes
Spiders- larger spiders
eaten by predators
-Smaller spiders can’t
catch enough food
-Favors average size

7. 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

8. 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

9. 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

10. 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

11. 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

12. *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

13. farm1.static.flickr.com/144/383488615_b937af4
lh3.google.ca/abramsv
farm1.static.flickr.com/144/ _b937af4
Photo Credit: AZ Herpetological Association
Photo Credit: Dan Hipes

14. Can you think of an example for camouflage?
I’ll show you some

15. *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

16. -Antibiotic resistance -Crop pest evolution MRSA podcast
Articles on:
-Antibiotic resistance
-Crop pest evolution
MRSA podcast
Strains of drug-resistant TB

17. *Indirect evidence for evolution
Fossils
Assembling a puzzle without all the pieces
What percentage of “Lucy” did they find?

18. *Indirect evidence for evolution
Anatomy (p. 401 fig. 15.6)
Homologous structures
Structural features with common evolutionary origin

19. *Anatomy cont. Analogous structures Vestigial structures
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

20. *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