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Evolution
Chapters 19 through 22
Learning Objectives
• Compare microevolution to
macroevolution
• Define and discuss natural selection
• Relate Darwin’s contributions to our
overall understanding of evolution
• Compare phenotype and genotype
• Apply the Hardy-Weinberg equation to
populations undergoing a shift in
equilibrium
Learning Objectives
• Define Convergence, Divergence,
Polymorphism, and Sexual Dimorphism
• Discuss speciation
• Explain prezygotic and postzygotic
mechanisms for speciation
Nature Changes
• Biogeography
– World distribution of organisms
– Global exploration raised difficult questions for
“unchanging creation”
• Comparative morphology revealed structural similarities
in “dissimilar” anatomies
– Vestigial structures currently useless structures
Large, Flightless Birds
Humerus
Ulna
Radius
Carpals
5
1
1
4
Digits
2
5
2
5
3
2
4
3 4
Foreleg of pig
3
Flipper of dolphin
Wing of bat
Fig. 19-3, p.403
19.2 Darwin’s Journeys
• Darwin saw the world on the voyage of the
Beagle
• Darwin used common knowledge and
several inferences to develop his theory
• Darwin’s theory revolutionized the way we
think about the living world
Darwin and the Beagle
• 1831 voyage of H.M.S. Beagle
– Timed well with modern geology
• Darwin observed global biogeography
– Fossils similar to extant organisms
– Organisms near each other similar even if in
different habitats
– Species change after isolation from ancestral
groups
Ancestors and Descendants
Ancestors and Descendants
Morphological Differences
Developing Darwin’s Theory
• Darwin tried to discover how species arise
– Finch island biogeography
• Artificial selection
– Process of improving organisms by selective
breeding
– Darwin tried to reconcile observation of
artificial selection with nature
Struggle for Existence
• Struggle for existence occurs when
resources limit reproduction of organisms
– All species reproduce faster than needed to
replace parent generation
Natural Selection
• Natural selection increases favorable
hereditary traits in successive generations
– Adaptive traits are genetic characteristics that
increase likelihood of reproduction
– Evolutionary divergence creates new species
over long time periods
Darwin’s Observations and
Inferences
Darwin’s Revolutionary Theory
• Darwin provided physical rather than
spiritual explanations
• Evolutionary change occurs in populations
• Evolution is a multistage process
– Variations, natural selection, inheritance
• Organisms function best in particular
environments
Early Theory of Evolution Tests
• Two perceived problems tested theory of
evolution:
– Darwin used complex trait examples, Mendel
simple traits
– Darwin studied gradual evolution, Mendel’s
mutations of simple traits had fast impact
• Population genetics linked Darwinian
evolution and Mendelian genetics
Modern Synthesis
• Modern synthesis unified theory of
evolution
– Combined all areas of biology under evolution
– Gradualism more important than dramatic
change
• Microevolution of populations and
macroevolution of life history act in concert
Evidence of Evolutionary
Change
• Adaptation by natural selection
– Long term evolutionary trends across species
(wings)
– Short term evolutionary trends within
populations (antibiotic and pesticide
resistance)
• Fossil Record
– Biological lineages such as birds from
dinosaurs
1. When mosquitoes were first exposed
to DDT, only about 5% of the population
was resistant and the insecticide killed
the remaining 95%.
2. Resistant individuals survived and reproduced,
passing the genes for resistance to the next generation.
Percentage killed
3. One year later, about
50% of the population
was resistant. The same
concentration of DDT
killed only 50% of the
population.
4. Resistant individuals again
survived and reproduced.
5. After just a few
more months, about
75% of the population
was resistant and the
same concentration of
DDT killed only 25% of
the population.
Months
Fig. 19-11, p.412
Bird Ancestry
Evidence of Evolutionary
Change
• Historical biogeography
– Study of organismal distribution in relation to
evolutionary history
– Island and continental biogeography
• Comparative morphology analyzes extant
and extinct structural relationships
– Homologous traits similar between species
due to common ancestry
– Human and bat forelimbs
Evidence of Evolutionary
Change
• Comparative embryology has shown
embryos from major groups
developmentally similar
– Gill pouches in humans and fish
• Genetic code independent evidence of
evolutionary relationships
– Closely related species have closely related
amino acid, nucleotide sequences
Human embryo
Adult shark
Fig. 19-13, p.414
Differences in Amino Acid Sequences
INSERT FIG 19.14 HERE
Macroevolution
• Microevolution is small changes within
a species; creating new alleles
• Macroevolution are large changes over a
geological time period that lead to
speciation
Phenotype vs. genotype
• Genotype= the genetic makeup of alleles
of an individual
– Homozygous=pp, qq
– Heterozygous=pq
• Phenotype= the expressed alleles
– pp=white, qq=black, pq=grey
• Some alleles are dominant, some
recessive, and some partial
Hardy-Weinberg Equilibrium
• p2 +2pq + q2 = 1.0
• If a population has 70% p alleles, then q
must be at 30%
• Evolution is a process resulting in changes
of genetic makeup over time
• Evolutionary agents are those that disrupt
the Hardy-Weinberg equation
Speciation
• Speciation
– Process of species formation
– Inferred by studying products, species
• Microevolutionary processes that lead to
population divergence produce new
species
Morphological Species Concept
• Based on differences in anatomical
features
– Only species definition for fossils
• May lead to erroneous conclusions
– Some anatomical differences within species
– Some species identical in appearance
– Not always evolutionarily based
Biological Species Concept
• Based on reproductive isolation
– If populations can interbred, they are
members of same species
– If populations do not make fertile offspring,
they are different species
• Problems with biological species
– Asexual and extinct organisms
Subspecies
Prezygotic Mechanisms
• Ecological isolation from habitats
• Temporal isolation from mating timing
• Behavioral isolation from mating signals, sexual selection
• Mechanical isolation from reproductive structures
• Gametic isolation from gamete incompatibility
Interspecific Hybrids
Postzygotic Isolating
Mechanisms
• Interspecies offspring reproductively isolated if
less fit than intraspecies offspring
• Hybrid inviability from species hybrids not
surviving
• Hybrid sterility from species hybrids
• Hybrid breakdown reduced fitness of F2
Macroevolution
• Microevolution is small changes within a
species; creating new alleles
• Macroevolution are large changes over a
geological time period that lead to
speciation
Convergent/Divergent Evolution
• Convergence=Similar adaptations in
distantly-related organisms- Similar selective
pressures produce similar adaptations
• Divergence= Very distinct differences in
closely related organisms
• Polymorphism- differences within a species
• Sexual Dimorphism- differences between
male and females of a species
Adaptive Radiation
• Biodiversity
– Number of species in given area
• Adaptive radiation
– Group of closely related species occupying
different habitats
– Ancestral species move into unfilled adaptive
zone (unoccupied or open from extinction)
Extinctions
• Background extinction rate
– Low rate, from environmental change and poor
adaptations
– Over global time scales, most species go extinct
• Mass extinctions
– High rate over short time
– Climate changes from geological activity and asteroid
impacts
Evo-Devo
• Evolutionary developmental biology (evodevo)
– Evolution in genes of embryonic development
– Genes of development also regulate
morphology
• Homeotic genes
– Control transcription of development genes
– Small changes in homeotic genes can
produce large changes in morphology
Homeotic Genes
• Many organisms share common genetic
tool-kit for development
– Common animal genes for 500 million years
– Common genes in animals, plants, fungi and
prokaryotes from earliest life
Hox Genes
• Control animal body plan
• Homeobox
– 180-nucleotide sequence
– Codes for homeodomain (part of a
transcription factor)