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EVOLUTION
Darwin’s theory of evolution by natural selection – On
the Origin of Species – 1859
1. Organisms produce more offspring than can
survive (Malthus)
2. Resources are limited
3. Individuals must compete for these resources
4. Variation exists in populations
5. Natural selection – individuals with beneficial traits
(adaptations), more likely to survive, leave more
offspring
“Fitness” - # of fertile offspring produced is the
measure
6. Adaptations passed onto next generation
Mechanisms of Evolution
Macroevolution – large scale, major change
-new trends, new species
Microevolution – changes of gene
frequencies within a population
Genetic variation–raw material for evolution
Gene pool – sum of all alleles of all genes of
all individuals in a population
*A change in gene pool  evolution
Allele Frequencies
What can change them?
1. Mutation
2. Migration – immigration or emigration
3. Genetic drift – in small populations
- random loss of alleles
4. Non random mating –if only certain
individuals mate
5. Selection - artificial (people choose) OR
- natural (environment selects)
*Natural selection is the most powerful –the only
one that  adaptive change
Hardy-Weinberg Principle
-If none of above occurs, allele frequencies will not
change
result is  genetic equilibrium
p2 + 2pq + q2 = 1
p – frequency of one allele
q – frequency of the other
p+q=1
(example on board)
Evidence for Evolution
Microevolution examples:
-peppered moths
-sickle cell anemia + malaria
-the lethal sickle cell allele remains in high frequency
where malaria occurs
-recent changes in finch beaks
-guppies (see graphic)
Macroevolution examples:
-paleontology (fossils)
-comparative anatomy :
homologies, vestigial structures
-embryology
-biogeography – convergent evolution
-biochemistry – similarities in proteins
- nucleotide sequences
Sources of variation in populations
Natural selection acts on variation
1.
2.
Mutation – only sources of new variation (new alleles)
Genetic recombination (sexual reproduction)
-crossing over
-independent assortment
-random gamete joining (fertilization)
3.
Diploidy – 2 copies of each gene
-can have 2 different forms (alleles)
-maintains diversity
4.
Symbiosis
-endosymbiosis, lichen, etc.
The Origin of Species
Speciation, Macroevolution
Species – definition?
Isolation:
-populations become separated (one way
or another)
-gene pools now isolated
-each gene pool changes over time
-each population becomes distinct species
Isolating Mechanisms
Prezygotic (Pre-mating):
1. Geographical – physical separation
2. Ecological – distinct habitat or niches
within region
3. Behavioral
4. Temporal – reproduction occurs at
different times
5. Mechanical – mating is physically impossible
6. Prevention of gamete fusion
-sperm and egg incompatible
Postzygotic:
1. Embryo dies
2. Hybrid weakness
3. Hybrid sterility
Divergent Evolution
1 species  2 or more species
Adaptive radiation:
-1 common ancestor  cluster of closely
related species
eg. Darwin’s finches
Placental mammals
Hybridization and Polyploidy –
can create new species in plants
Types of Selection
Sexual Selection
-when one gender (usually males)
competes to mate with the other gender
-often females choose mates
-selection is for (examples):
-large body
-horns, antlers
-colorful plumage
-certain behaviors
Primate Evolution
Prosimians (40 million years ago):
-grasping fingers and toes
-binocular vision
-lemurs are modern prosimians
Apes, monkeys
-monkeys – even better vision
-opposable thumb
-complex social behavior
-learning (extended parental care)
-large brains
-apes – hominoids (15 million years ago)
Hominids -humans and extinct ancestors
- bipedal, larger brains
(extensive use of tools, language)
-Australopithecus
-Homo habilis
-Homo erectus
-Homo sapiens (500,000 years ago)