2. Descent with Modification
Theme:
• Evolutionary change is based on the
interactions between populations & their
environment which results in adaptations
(inherited characteristics) to increase fitness
Evolution = change over time in the genetic
composition of a population
3. Charles Darwin (1809-1882)
• English naturalist
• 1831: joined the HMS Beagle for
a 5-year research voyage around
the world (stopped at: Galapagos
Islands)
• 1859 – published Origin of
Species
• Influenced by Lamarck, Hutton &
Lyell, Malthus
4. Darwin’s Theory of Natural
Selection:
1. Populations produce more offspring than can
possibly survive.
2. Individuals in a population vary extensively from
each other, mostly due to inheritance.
3. Struggle to survive: individuals whose inherited
characteristics best fit to environment leave more
offspring than less fit.
4. Unequal ability of individuals to survive and
reproduce leads to gradual change in pop, with
favorable characteristics accumulating over
generations.
5. • Populations evolve, not individuals.
• Fitness is determined by the environment.
In summary:
Natural Selection = differential success in
reproduction
Product of natural selection = adaptations of
populations to environment
6. Therefore, if humans can create substantial
change over short time, nature can over
long time.
Natural Selection Artificial Selection
•Nature decides •“Man” decides
•Works on individual •Selective breeding
•Inbreeding occurs
•i.e. beaks •i.e. dalmations
7. Evidence for Evolution
1. Biogeography
▫ Geographic distribution of a species
▫ Geographic, reproductive isolation
2. Fossil Record – transitional forms
3. Comparative Anatomy
1. Homologous structures
2. Vestigial structures
4. Embryonic Development
5. Molecular Biology
▫ DNA, proteins
10. Learning Objective:
To analyze the conditions required for the
“ Hardy Weinberg Equilibrium”
To solve the problems related to the Hardy
Weinberg Equilibrium
• To analyze the conditions required for the “ Hardy Weinberg Equilibrium”
• To solve the problems related to Hardy Weinberg Equilibrium.
11. Population Genetics = Foundation for
studying evolution
• Darwin’s could not explain how inherited
variations are maintained in populations - not
“trait blending”
• A few years after Darwin’s “Origin of Species”,
Gregor Mendel proposed his hypothesis of
inheritance:
Parents pass on discrete heritable units (genes)
that retain their identities in offspring
12. Hardy-Weinberg Theorem:
• Frequencies of alleles & genotypes in a
population’s gene pool remain constant from
generation to generation unless acted upon by
agents other than sexual recombination (gene
shuffling in meiosis)
• Equilibrium = allele and genotype frequencies
remain constant
13. Conditions for Hardy-Weinberg Equilibrium:
1. Extremely large population size (no genetic
drift).
2. No gene flow (isolation from other
populations).
3. No mutations.
4. Random mating (no sexual selection).
5. No natural selection.
14. Hardy-Weinberg Equilibrium
Allele Frequencies:
• Gene with 2 alleles : p, q
p = frequency of allele “A” in a population
q = frequency of allele “a” in a population
p + q = 1
Note:
1 – p = q
1 – q = p
19. Learning Objective:
To analyze the causes of Microevolution.
• To analyze the conditions required for the “ Hardy Weinberg Equilibrium”
• To solve the problems related to Hardy Weinberg Equilibrium.
20. • If any of the Hardy-Weinberg conditions are not
met microevolution occurs
• Microevolution = generation to generation
change in a population’s allele frequencies
21. Main Causes of Microevolution
1. Mutations – changes in DNA
Point mutations
Gene duplication
Mutation will
alter or create
new alleles in a
population.
22. Main Causes of Microevolution
2. Sexual Recombination
▫ Rearrange alleles into fresh combinations every
generation
23. Main Causes of Microevolution
3. Natural selection
Douglas fir trees only release their seeds during fires.
Fire rarely occurs in the river bottom of this valley.
24. Main Causes of Microevolution
4. Genetic drift: a change in a population’s allele
frequencies due to chance
bottleneck and founder effect
25. A. Bottleneck Effect – genetic drift due to drastic
reduction in population size
▫ Certain alleles may be over/under represented
Northern elephant seals hunted
nearly to extinction in California
26. B. Founder effect – few individuals become
isolated from larger population certain
alleles over/under represented
Polydactyly in Amish population
27. Main Causes of Microevolution
5. Gene flow – genetic exchange due to migration
of fertile individuals
i.e. wind storm blows pollen to another field
Reduces differences between populations
Gain/lose alleles
28.
29. Fitness : the contribution an individual makes to
the gene pool of the next generation
Natural selection can alter frequency distribution
of heritable traits in 3 ways:
1.Directional selection
2.Disruptive (diversifying) selection
3.Stabilizing selection
30. Directional Selection:
eg. beak sizes of birds
during wet/dry
seasons in Galapagos
Diversifying Selection:
eg. small beaks for
small seeds; large
beaks for large seeds
Stabilizing Selection:
eg. average human
birth weight
31. Preserving Genetic Variation
• Diploidy: inherit 2 alleles
Recessive alleles less favorable
Heterozygote protection
• Heterozyote Advantage:
People hybrid for sickle cell anemia protected
against malaria.
32. • Sexual selection for mating success
▫ Intra (within same sex) – competition for mate
▫ Inter (out) – mate choice
Darwinian Fitness : ability to survive AND
reproduce AND pass on alleles to offspring
Sexual selection may lead
to pronounced secondary
differences between the
sexes
33. Evolution of Populations
• Remember:
▫ Individuals are selected
▫ Populations evolve
• Terms:
▫ Population = localized group belonging to same
species
▫ Species = members of a population that can interbreed
and produce fertile viable offspring
▫ Gene pool = total combo of genes in a population at
any one time
▫ Fixed population = all members are homozygous for
trait (usually not the case)
34. Speciation = origin of species
• Microevolution: changes within a single gene pool
• Macroevolution: evolutionary change above the
species level
▫ cumulative effects of speciation over long periods of
time
Similarity between different species.
36. Anagenesis (“new” “race”)
• Phyletic evolution
• A single species gradually
changes into a different
species
• No original group left
• Evolution in single direction
Cladogenesis (“branch” “race”)
• Branching evolution
• One species stays same, but small
portion leaves and changes to
another species
• Gene pool splits
• Original + new groups
• Increase in diversity/# of species
Two Patterns of Evolutionary Change
37. Biological Species Concept
• Proposed by Ernst Mayr (1942)
• Species = population or group of populations
whose members have the potential to interbreed
in nature and produce viable, fertile offspring
▫ Reproductively compatible
• Reproductive isolation = barriers that prevent
members of 2 species from producing viable,
fertile hybrids
39. Other definitions of species:
• Morphological – by body shape, size,
and other structural features
• Paleontological – fossil record
• Ecological – niche/role in community
• Phylogenetic – unique genetic history,
branch on tree of life
43. Two main modes of speciation:
Allopatric Speciation
“other” “homeland”
Geographically isolated
Evolves by natural selection
& genetic drift
Eg. Galapagos finches
Sympatric Speciation
“same” “homeland”
Overlapping populations
within home range
Subset of population isolated
from parent pop. change
due to:
• chromosomal changes
• nonrandom mating
• habitat differentiation
Eg. polyploidy in plants (oats,
cotton, potatoes, wheat)
44. Adaptive Radiation
• Emergence of numerous species from a common
ancestor introduced into new environment
• Occurs when:
A few organisms make way to new, distant areas
(allopatric speciation)
Environmental change extinctions new
niches for survivors
• Eg. Hawaiian archepelago
Founding
Parents
45. When 2 splintered groups rejoin geographically:
Possibilities:
1. Still one species
2. Two distinct species (no interbreeding)
3. Hybrid zone
A B
Interbreeding
zone
46. Gradualism
• Darwin
• Slow, constant change
• Less likely
Punctuated Equilibium
• Eldridge & Gould
• Long period of minor change
are interrupted by short
bursts of significant change
• More likely
Tempo of Evolution
47. Convergent Evolution
• Independent development of similar features
between 2 unrelated species
• Similar environments
• Analogous structures
• Eg. wings on bees & wings on birds
48. REMEMBER!!
•Dear King Philip Came Over For Good
Spaghetti
•Dear King Philip Crossed Over Five
Great Seas
•Dear King Philip Came Over From
Germany Stoned
•Your own???
49. • Phylogeny = evolutionary
history of a species or group
of species
Phylogram: the length of a branch
reflects the number of changes that
have taken place in a particular DNA
sequence in that lineage
50. • Cladogram: diagram of evolutionary relationship of
organisms
▫ Shared characteristics due to common ancestry
▫ Uses parsimony – simplest explanation, fewest DNA
base changes for tree (“keep it simple”)
Cladistics : a form of systematics
LE
25-
11b
Turtle Leopard
Hair
Amniotic egg
Four walking legs
Hinged jaws
Vertebral column
Salamander
Tuna
Lamprey
Lancelet (outgroup)
Cladogram
51. Comparison of Structures
Homology Analogy
• Results from:
▫ Adaptive radiation
▫ Common ancestor
▫ Similar origin
• Different functions
• Eg. wing of bat, human arm,
dolphin flipper
• Results from:
▫ Convergent evolution
▫ Different ancestors
▫ Different origin
• Similar functions
• Eg. wings of bird, wings of
insect
Remember:
•Adaptive radiation – emergence of many species from common ancestor
•Convergent evolution – unrelated species independently evolve
similarities when adapting to similar environments
52. Major events during each Era
• Precambrian: microscopic fossils (stromatolites)
▫ Photosynthesis, atmospheric O2
▫ Eukaryotes (endosymbiont theory)
• Paleozoic: Cambrian Explosion
▫ Plants invade land, many animals appear
▫ Permian Extinction (-96% species)
• Mesozoic: “Age of Reptiles”, dinosaur, plants
▫ Formation of Pangaea supercontinent
▫ Cretaceous Extinction – asteroid off Mexico’s coast
• Cenozoic: primates
Note: All end with major extinction & start with
adaptive radiation
53. Land plants
Animals
Ceno-
zoic
Origin of solar
system and
Earth
4
1
2 3
Multicellular
eukaryotes
Single-celled
eukaryotes
Prokaryotes
Atmospheric
oxygen
Proterozoic
Eon
Archaean
Eon
Humans
Billions of years ago
Clock Analogy
of Earth’s
History
54. Evolution of Plants
• Non-Vascular (liverworts, hornworts, mosses)
Seedless Vascular (ferns) Seed Vascular
(gymnosperms, angiosperms)
• Mosses: Gametophytes = dominant form
• Ferns: 1st with vascular tissue (xylem, phloem
▫ wet environment (fertilization in water)
▫ Sporophyte = dominant form
• Gymnosperms: “naked” seeds on cones
▫ Conifers
• Angiosperms: flowering plants