Evolution
1. Darwinian vs. Lamarckian View
a. Darwinian: being born with beneficial
traits allow better survivorship of certain
animals which pass on the traits to next
generation
b. Lamarckian: traits are acquired through
demands of the environment and the
acquired traits are transmitted to next
generation
2. Natural Selection
a. Variation: differences in populations due
to random mutations
b. Competition due to over-production of
offsprings
i. Competition for food, water,
habitat and means of escape from
predators
c. Differential Survival: successful traits
allow better survival rates= adaptations
d. Differential reproduction: successful
adaptations are passed down to next
generations and become more prominent
3. Major Causes of Evolution
a. Gene Flow
i. Migration introduces new traits
into a population
b. Genetic Drift: chance events change
frequency of traits in a population
i. Founder Effect: small group
separates and reproduces to start a
new colony from that limited
gene pool
ii. Bottleneck: random event or
disaster decimates population and
reduces gene pool
c. Mutation: random changes in DNA
sequences cause changes in expressed
traits with variable survivorship
d. Natural Selection: traits are acted upon
i. Predation Selection: act on both
predator and prey
1. Predator: speed and other
means of obtaining prey
2. Prey: defenses such as
mimicry, crypsis and
other means of avoiding
predators
ii. Physiological Selection: act on
body functions
1. Disease resistance
2. Efficiency in obtaining
materials (O2, H2O,
nutrients) and getting rid
of wastes (CO2, etc)
3. Biochemical Versatility:
means of homeostasis
iii. Sexual Selection: act on
reproductive success
1. Attractiveness (indicator
of fitness) to mate
2. Fertility of gametes:
ability for sperm and egg
to unite and successfully
form a zygote
3. Successful rearing of
offspring into
reproductive adults
4. Hardy Weinberg Equilibrium used to determine
whether a population is not or is evolving due to an
external factor (comparison of Hardy Weinbergpredicted frequency to actual sample)
i. Alleles: p + q = 1
1. p= frequency of
dominant allele
2. q= frequency of
recessive allele
ii. Individuals: p2 + 2pq + q2 =1
1. p2= p x p
a. Frequency of
homozygous
dominant
2. 2pq= p x q
a. Frequency of
heterozygote
3. q2= q x q
a. Frequency of
homozygous
recessive
5. Speciation: formation of new species through
isolation and independent (of each other) evolution
a. Allopatric vs. Sympatric
i. Allopatric: geographically
separated
ii. Sympatric: still in same area
b. Pre-reproduction barriers
i. Geographic isolation: living in
separate areas (allopatric)
1. Ex: 2 different species of
squirrels living in 2
opposite sides of canyon
ii. Ecological isolation: living in
same region but occur in different
niches (sympatric)
1. Ex: Lions (grasslands)
and tigers (rainforest)
may actually produce
ligers if they encounter
each other
iii. Temporal isolation: mating
during different times of the day
1. Ex: skunks that breed at
night vs. skunks that
breed during the day
iv. Behavioral isolation: unique
rituals or behaviors differentiate
species
Evolution
1. Ex: courtship and mating
calls of birds
v. Mechanical isolation: sexual
organs do not fit
1. Ex: damsel fly genitalia
vi. Gametic isolation: sperm can’t
fertilize egg because of
biochemical incompatibility
(sperm can’t penetrate egg) or
chemical incompatibility (sperm
can’t survive in female
reproductive tract)
1. Ex: red and purple sea
urchin gametes can’t fuse
c. Post-reproduction barriers: inability to
produce offspring that can develop into
viable, fertile adults
i. Reduced hybrid viability: parent
species’ genes may impair
hybrid’s development
1. Ex: frail salamander
hybrids
ii. Reduced hybrid fertility: sterile
offspring can’t reproduce due to
odd number of chromosomes that
can’t produce normal gametes
1. Ex: donkey (31) + horse
(32) = mule (63)
iii. Hybrid breakdown: hybrids
viable and fertile but produce
feeble or sterile offspring
1. Ex: hybrid rice may
thrive but offsprings are
small and sterile
6. Evidence for Evolution
a. Fossil Evidence: fossil records show
succession of simple to more complicated
organisms or transitional links between 2
groups of organisms
i. Ex: archaeopteryx is transitional
link between birds and reptiles
b. Anatomical Evidence:
i. Homologous structures: same
structures but may differ in
function
1. Similar structure
inherited from common
ancestor
2. Ex: bird, bat, whale cat,
horse & human bones in
extremities (wings vs.
flippers vs. legs vs. arm)
ii. Analogous structures: same
function but different structures
1. Different structures do
not prove common
ancestry
2. Ex: bird wings vs. insect
wings
iii. Vestigial structures: structure
fully developed in one group of
organisms but with reduced or no
function in similar groups
1. Similar vestigial
structures support
common ancestry
2. Ex: bird vs. human
tailbone
c. Biogeographical evidence: distribution of
plants and animals in different places
throughout the world
i. Related forms evolve in one
locale or similar environments
ii. Ex: marsupials in Australia/ both
succulent, spiny angiosperms:
cacti in North American deserts
and euphorbias in African deserts
d. Biochemical evidence: same basic
biochemical molecules (DNA, ATP,
enzymes) in living organisms
i. Ex: similar amino acid sequence
in cytochrome c ( ETC protein) in
organisms
e. Artificial record: artificial breeding to
create varieties
i. Ex: domesticated dog breeds=
descendants of wolves/ lettuce,
Chinese cabbage & Brussels
sprouts= descendants of Brassica
Oleracea
7. Coevolution vs. Parallel vs. Convergent Evolution
a. Coevolution: 2 or more species affect each
other’s evolution
i. Predator-prey & parasite-host
relationship
ii. Mutualism
Ex: pollinators and flowers
b. Parallel Evolution: 2 species from same
recent common ancestor go through same
evolutionary changes as a response to
similar environmental condition
i. Ex: complex plumage patterns
that seem to have evolved
independently in different bird
species
c. Convergent Evolution: “similar solutions
to similar problems”; involve analogous
structures
i. Ex: wings in bats, birds, and
insects for flight/ tails and
flippers in dolphins (aquatic
mammals) and fish (aquatic
vertebrates)