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EVOLUTION
Date:
evolution: Δ over time
 process by which modern organisms have descended from others
theory: well-supported, testable explanation for natural phenomena
15-3: Darwin presents his case (p.378)
*On the Origin of Species published in 1859
 Darwin observed variation in nature & on farms
o genetic (inherited) variation – differences passed from parents to offspring
o artificial selection – humans breed organisms w/ desired traits (fig.15-10)
* Natural Selection
 struggle for existence – organisms compete to obtain food, living space, other necessities
 fitness – ability to survive & reproduce in a specific env
 results from adaptations – inherited characteristics that ↑ chance of survival
 can be anatomical (structure), physiological (fxn), or behavioral
 survival of the fittest – ind better suited to their env survive & repr. most successfully
 natural selection – results in Δ’s in inherited characteristics of a population, ↑’ing fitness of a
species (spp) in its env  after many generations
 common descent – all spp were derived from common ancestors
Date:
*Evidence of Evolution (p.382)
A. Fossil Record
o Fossils: preserved remains of ancient organisms
B. geographic distribution of spp
C. homologous structures: dif mature forms but develop from the same embryonic tissues (fig 15-15)
o showed common descent of 4-limbed vertebrates
o vestigial organs – serve no useful function
 unaffected by natural selection
D. comparing DNA
E. similarities in embryology (fig 15-17)
o groups of embryonic cells develop in same order & patterns  homologous structures!
Evolution: “the grand unifying theory of the life sciences”
Date:
16-1: Genetic Variation (p.393)
 ↑’s chance that some members of spp survive Δ’s in env.
 studied in populations – group of individuals of same spp
 gene pool: all genes/alleles in a pop.
 relative frequency: # of times an allele occurs in a gene pool compared to other alleles
for same gene (fig 16-2)
 evolution is any Δ in relative frequency of alleles in a pop.
 2 sources:
1. mutations – any Δ in DNA sequence
 result from (a) mistakes in DNA replication or (b) chemicals/radiation
 can be “silent” – do not Δ AA  no effect on phenotype
2. gene shuffling (sexual reproduction)  does NOT affect allele frequencies
Date:
16-2: Evolution as Genetic Change (p.397)
* natural selection NEVER acts directly on genes; only organisms (phenotype not genotype!)
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NS on single-gene traits (fig 16-5)
 can lead to Δ’s in allele frequencies
NS on polygenic traits (controlled by >1 gene)
1. directional selection – occurs when ind. at 1 end of bell curve have higher fitness
than those in middle or other end (fig 16-6)
2. stabilizing selection – ind. near center of curve have highest fitness (fig 16-7)
3. disruptive selection – ind. at upper & lower ends of curve have highest fitness (fig 16-8)
 can cause split into 2 distinct phenotypes
genetic drift – random Δ in allele freq.  can reduce genetic variation (fig
 founder effect – migration of some members of pop.
Date:
16-3: Speciation (p.404)
* speciation: formation of a new spp
 if a genetic Δ in 1 ind. ↑’s fitness, allele will eventually be found in many ind.
 diversity of spp ↑’s chance that some organisms survive major Δ’s in env
* reproductive isolation – occurs when 2 pop. no longer interbreed
 separate gene pools form  speciation
 develops from:
1. behavioral isolation –2 pop. have differences in reproductive strategies
2. geographic isolation – 2 areas are separated by geographic barriers (rivers, mount, lakes, etc)
3. temporal isolation – 2 or more spp reproduce at dif times
Date:
17-1: The Fossil Record (p.417)
Interpreting Fossils
1. relative dating –compare placement w/ fossils in other rock layers
 younger layers are above older layers
 index fossils – easily recognized spp that existed for short time but over wide geographic
range
2. radioactive dating – use of half-lives to determine absolute age of rocks (fig 17-4)
 half-life: length of time for ½ of radioactive atoms in a sample to decay
Geologic Time Scale – organized by age of rock layers where major Δ’s in fossils occurred (fig 17-5)
 time btwn Precambrian & present divided into 3 eras:
1. Paleozoic
2. Mesozoic
3. Cenozoic (most recent)
 Eras are divided into periods
Date:
17-3: Evolution of Multicellular Life
*88% of Earth’s history was during Precambrian
 1st organisms were prokaryotic
 Paleozoic Era
o “Cambrian Explosion” – great diversification of life forms
o Permian mass extinction
 95% of complex ocean life disappeared
 Mesozoic – age of reptiles
o Cretaceous mass extinction (dinosaurs, ½ of all plant & animal groups)
 Cenozoic – age of mammals
Date:
17-4: Patterns of Evolution
*macroevolution: large-scale evolutionary patterns & processes that occur over long periods of time
 extinction
o 99.99% of spp that ever lived are extinct
o mass extinctions opened new habitats & added ecological opportunities  rapid evolution
 adaptive radiation – single spp evolves into diverse forms that live differently
 convergent evolution – unrelated organisms come to resemble one another (fig 17-23)
 coevolution – 2 spp evolve in response to Δ’s in each other
o flowering plants & insects
 genes
o hox genes – guide development of major body structures in animals