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EVOLUTION
Date:
CH 13: How Populations Evolve (p.256)
Darwinism
 Evolution: inherited Δ in organisms over time
 Theory: well-supported, well-tested explanation for natural phenomena
 On the Origin of Species (1859) revealed Darwin’s theory of natural selection as the mechanism for evolution
o Conflicted w/ hypothesis of Jean-Baptiste Lamarck that said use & disuse leads to acquired
characteristics that can be inherited by offspring
o Observations:
 there is variation in nature, much of which is heritable (genetic)
 the size of a pop. tends to remain stable
 Resources become limited as pop. density ↑’s
o Inferences:
 There is a struggle for existence among members of a pop.
 Survival depends on inherited characteristics called adaptations that ↑ fitness (the ability to
survive & reproduce) in a SPECIFIC env
 Adaptations will become more common over time
Date:
Natural Selection (survival of the fittest) – individuals better suited to their env. survive & reproduce most
successfully
o Dependent on genetic variation & specific env./habitat
o Can only edit existing characteristics; does not create new ones
 Ex: wings evolved from appendages that were not used for flying; our knees & backs were
derived from 4-legged animals, & this partly explains why people frequently have knee & back
problems
o Does not lead to “perfect” individuals
o It is situational
 Adaptations in 1 env. may be useless or harmful in another env.
o Populations evolve, not individuals
 Species (spp): group of individuals (pop.) that interbreed & produce fertile offspring
Date:
Evidence of Evolution (p.260)
A. Fossils: preserved remains of ancient organisms
o The Fossil Record is incomplete b/c most organisms do not form fossils & they are hard to find
o Age is determined by:
 Relative dating - compare placement w/ fossils in other rock layers
 Radiometric dating - use of isotope half-lives to determine absolute age of rocks
B. Biogeography
o Spp tend to be more closely related to other spp from the same area than to spp in dif areas
w/similar conditions
 Ex: Darwin noticed similarities b/w organisms on the Galapagos & S. America that were
dif from organisms living in similar climates on other continents
C. Comparative Anatomy: shows evolution is a remodeling process that alters existing structures
o Homologous structures: have dif. fxns but similar structure
 Evidence that spp share a common ancestor
o Analogous structures: same fxn & form; evolved independently from dif ancestors
 Shows that adaptations develop in certain env.
Vestigial structures: functioned in ancestors but not in modern spp
 Unaffected by NS because they do not HARM the organism
 Ex: whale fossils w/ pelvic bones
o Comparative embryology
 Embryos look very similar & start to differ as they develop
 Suggests spp descended from a common ancestor
D. Molecular Biology
o Universal genetic code (DNA)
o Certain genes are conserved across dif spp
 Ex: developmental genes, hemoglobin in vertebrates
o More differences in DNA or AA sequence of protein indicates more distantly related spp
E. Observational Evidence
o Shifts in frequency of finch beak sizes in response to drought
o Antibiotic resistance in bacteria
o Insecticide resistance in insects
o Herbicides resistance in plants
o
Date:
Microevolution (p.268)
 Gene pool: total # of genes in a pop.
 Microevolution: Δ w/in a spp that lead to Δ’s in allele frequencies
o Greater variation ↑’s chances of some members of a spp surviving Δ’s in the env
 Macroevolution: Δ that occurs as new spp evolve
o Results from the accumulation of small Δ’s over time in separate pop.
 Hardy-Weinberg equilibrium predicts the gene pool of a pop that is NOT evolving
o 5 standards of HW:
1. Infinite pop size
2. Mating is random
3. No mutation
4. No migration in or out
5. No selection (all genotypes confer equal fitness)
o HW equilibrium rarely occurs in nature but can be used to predict allele frequencies in a pop & analyze
the causes of evolution
o HW equations:
 p+q=1
 p2 + 2pq + q2 = 1
- p = frequency of dominant allele
- q = frequency of recessive allele
- p2 = frequency of homozygous dominant
- 2pq = frequency of heterozygous
- q2 = frequency of homozygous recessive
Date:
Causes of Microevolution (p.270)
A. Natural selection
B. Genetic drift: Δ in allele frequencies due to chance – can lead to ↓ in genetic variation
o More of 1 allele might be inherited than another
o Bottleneck effect: genetic drift from a drastic ↓ in pop size due to an environmental event
o Founder effect: genetic drift from a small # of ind. colonizing a new area
C. Gene Flow: migration of ind. or gametes b/w pop.
o May ↓ genetic differences in populations
D. Mutation: random Δ in DNA produces a new allele
o
Rare b/c most mutations have no effect (silent) or are harmful/lethal (deleterious)
Date:
Types of Selection (p.276)
 Stabilizing selection favors avg. ind.
o Occurs in stable environments
o ↓’s variation
o Ex: human birth weight
 Directional selection favors 1 phenotypic extreme
o Most common during environmental Δ’s or when spp migrate to a new habitat
o Ex: selection of longer horns in Texas longhorns
 Disruptive/diversifying selection favors both phenotypic extremes
o Common in variable env.
o Ex: beak size in finches
 Sexual selection: mates are chosen based on phenotype
o May lead to sexual dimorphism: males & females look dif
 Traits often indicate high fitness
- Ex: peacock w/ big, colorful feathers that survives predators despite attracting them
 Artificial Selection: selective breeding of plants & animals by humans
Date:
Speciation (p.284)
 Formation of new spp is dependent on reproductive isolation: 2 pops stop interbreeding
 May result from:
o Temporal isolation – 2 pop breed at dif times
o Habitat isolation – geographic barriers separate 2 pop
o Behavioral isolation – 2 pop have dif reproductive strategies
 Ex: mating behaviors