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Evolution
Content• 1. An introduction to evolution
• 2. Historical view (the evolutionary thinking)
• 3. Genetic variation
• 4. Mechanisms: the processes of evolution
• 5. Microevolution vs Macroevolution
• 6. Speciation
• 7. Issues on evolution
Evolution
Evolution = Change.
Biological Evolution = Change in the intrinsic qualities of life over time.
NOT progressive change.
What can change?
Characteristics of species
Number of species
EvolutionMicroevolution = Change in the
genetic qualities of populations within a species over time.
Macroevolution = Change in the number of species and the formation of groups of species.
Speciation = formation of species
Results of Evolution
• Anagenesis = change within a species lineage(number not increase)
• Cladogenesis = change and diversification
History: Early 1800’s
Natural Theology
Discover God’s plan, study nature.
Essentialism = Organisms are imperfect reflections of perfect eternal “essences.” (invariant)
Natural groups reflect the essential groups in the mind of God.
History: Early 1800’sPaleontology = study of fossils.
Fossil = preserved remnant of an organism that lived in the past
Certain fossils only found in certain rock strata (layers).
Some organisms are extinct!
Earth = VERY OLD
Sedimentary Rocks = layered rocks formed by settling particles.
Sedimentary Rocks & Fossils
oldest layer
youngest layer
Sedimentary Rocks & Fossils
Dead Thing
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
EROSION
Sedimentary Rocks & Fossils
Fossil (Dead Thing)
Sedimentary Rocks
Geologic Time ScaleGeologic scale based on the fossil
record. (time divisions UNequal)
Eras = four largest time periods (Precambrian --> Paleozoic --> Mesozoic --> Cenozoic)
Periods subdivide eras.
Mass Extinction = extinction of a large proportion of existing species.
They separate many eras or periods.
Geologic Time Scale
Cenozoic
Mesozoic
Paleozoic
Precambrian
extinction of dinosaursfirst flowering plants
first dinosaurs & mammals
“fern” forests form coal
first vertebratesfirst land plants & animals
near present oxygen levels
Eons
Eons = hundreds of millions of years in duration(บรมยุ�ค)
Eras(มหายุ�ค)
period(ยุ�ค)
epochs.
Biostratigraphy: The organisation of sedimentary rocks into units on the basis of the fossils they contain
Biostratigraphy:
Charles Darwin
Mid-1800’s, Charles Darwin
Studied medicine & theology
Traveled on H. M. S. Beagle
Bred pigeons
The Origin of Species, 1859TWO big ideas
Common Descent (old idea)
Natural Selection (new idea)
Natural SelectionMechanism of change
within one species. (Proposed by Darwin.)
Microevolutionary process.
First evidence from plant and animal breeding by humans
to create domestic forms.
Natural SelectionPopulations can grow tremendously.
In nature, populations remain stable in size due to limited resources (K).
THEREFORE, there is a struggle to survive and reproduce within species.
Organisms vary in inheritable characteristics (genetic).
THEREFORE, reproduction varies based on differences in inherited traits.
Natural Selection
DEFINITION
Differential reproduction (survival) based on
differences in inherited characteristics.
NOT “survival of the fittest”
Population
Population
Population
Population
Population
Population
Population
FitnessFITNESS = the relative contribution
of an individual to the next generation
More fit = more surviving offspring
Less fit = fewer surviving offspring
“Survival of the fittest” = circular, non biological statement
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Adaptation
Adaptation = characteristic that results from natural selection also...
a trait that enhances the reproductive success of the bearer.
Not ALL characteristics of organisms are “adaptations.”
Difficult to provide evidence that a characteristic is truly an adaptation.
Laboratory Selection
ลายุจุ�ดบนตั�วปลาหางนกยุ�งส่�วนใหญ่�ถู�กควบค�ม
ด�วยุพั�นธุ�กรรม ลายุจุ�ดน��ช่�วยุในการพัรางตั�วให�เข้�าก�บส่!"งรอบข้�างเพั$"อป%องก�น
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กว�าตั�วที่�"ไม�ม�ลายุจุ�ด จุ+ง ด+งด�ดค��ผส่มพั�นธุ�-
Microevolution
Sexual Selection
“Special” Kinds of Selection
Natural Selection = differential reproduction (survival) based on differences in inheritable characteristics (different alleles).
Sexual Selection = natural selection based on mate choice.
Artificial Selection = natural selection due to conscious human choice. (e.g., dogs, wheat)
Sexual Selection
Artificial Selection
Artificial Selection
p. 399
Population Genetics
Population = localized group of individuals of the same species
Population genetics = studies the genetic variation within populations
Genotype = the genes (alleles) possessed by an organism
Phenotype = the physical characteristics of an organism
Genetics “Review”
Genes (DNA) in cells direct cell activities.
Most cells have TWO copies of every gene. (DIPLOID)
One copy from each parent.
Sperm or egg have ONE copy of every gene. (HAPLOID)
Genetics “Review”
Genetics “Review”
The same gene can have different forms (Alleles).
E.g., blue iris allele and brown iris allele of eye color gene
Diploid individual with the same 2 alleles = homozygote.
Diploid individual with 2 different alleles = heterozygote.
Genetics
Gene “A” has 2 alleles,
“A” and “a.”
AA or aa = homozygotes.
Aa = heterozygotes.
AA, Aa, and aa = genotypes.
Calculation of allele frequencies.
Population GeneticsGene pool = all the alleles in a
population
Genetic structure = frequencies (%) of alleles and genotypes in a population.
Mendelian population = interbreeding group within a population.
Hardy Weinberg
Hardy-Weinberg Theorem = describes a population that is NOT evolving.
p2 + 2pq + q2 = 1
p = frequency of A in the pop.
q = frequency of a in the pop.
p + q = 1
P(A)=p P(a)=q
P(A)=p
P(a)=q
AA=p2 Aa =pq
AA + 2Aa + aa = p2 + 2pq + q2 = 1
Random mating
aA=pq aa=q2
(p+q) 2 = 1
p+q = 1
Hardy Weinberg
p2 + 2pq + q2 = 1
p2 = frequency of AA in the pop.
2pq = frequency of Aa in the pop.
q2 = frequency of aa in the pop.
Hardy-Weinbergp2 + 2pq + q2 = 1
The frequency of AA in a population at H.-W. equilibrium is
0.25.
What is the frequency of Aa in this population?
Hardy-Weinberg
p2 + 2pq + q2 = 1
p2 = 0.25
p = 0.5
p + q = 1 0.5 + q = 1
q = 0.5
Hardy-Weinberg
p2 + 2pq + q2 = 1
p = 0.5 q = 0.5
2pq = frequency of Aa
2(0.5)(0.5) = frequency of Aa
0.5 = frequency of Aa
Microevolutionary ProcessesMicroevolution = small
scale evolutionary changes.
Natural Selection
Non-random mating
Genetic Drift
Gene Flow (Migration)
Mutation
MutationMutation = introduction of random
genetic variation. Source of new alleles.
THE SOURCE of variation.
Change in the DNA (in a sex cell).
Relatively rare and random.
Some chemicals can increase mutation rate (mutagens).
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ร�นแรง เพราะยุ�นที่��ที่%าหน&าที่��ควบค�มอาจม�อ�ที่ธิ�พลต�อยุ� นอ(�นๆหลายุยุ�น
• ม�วเที่ชั�นที่��ยุ�นควบค�มส่�วนใหญ่�จ"งที่%าให&ไซึ่โกตตายุ ต�วอยุ�างของ nonlethal regulatory mutations ที่��เก�ดก�บ HOX genes ในมน�ษยุ�ซึ่"�งอาจก�อเป็0นผลให&เก�ด
ล�กษณะ polydactyly ซึ่"�งหากให&ผลด�ก2จะกระจายุไป็ในป็ระชัากร
Gene Flow
Gene flow = Gaining alleles from or losing alleles to another population.
Fertile individuals (emigration & immigration)
Seeds
Pollen
Gametes
Genetic Drift
Changes in the gene pool of a (small) population due to chance.
Chance =
random catastrophes
random individuals begin a pop.
genes randomly passed on to offspring
computer_drift_v2[1].swf
Genetic Drift
Genetic Drift
Genetic Drift
Genetic Drift
Genetic Drift
Population Bottleneck = genetic drift in small remnant population that later becomes larger. Result: a large genetically similar population
Founder effect = genetic drift in small founding population that later becomes larger. Example: polydactyly in the Amish
Population Bottleneck
p. 403
Population Bottleneck
time
#Much
Genetic Drift
GeneticVariation
No GeneticVariation
LargePopulation
LargePopulation
SmallPopulation
Cheetahs
Founder Effect
time
#
time
#
GeneticVariation
No GeneticVariation
Zoo Animals
Nonrandom MatingAssortative Mating = preferentially
mating with either similar or different genotypes.
Inbreeding = reproducing with relatives; increases homozygosity.(More likely to get 2 copies of the same bad gene. INCEST TABOO)
Outbreeding = reproducing with non-relatives; increases heterozygosity.
Natural Selection
Phenotype can be determined by a single gene or by many genes.
Stabilizing selection = removes extremes.
Directional selection = Removes ONE extreme.
Disruptive selection = Removes intermediates; favors extremes.
Quantitative Characters
One Gene Characteristic
#
Many Gene Characteristic
#
Directional Selection
#
p. 405
Distribution
#
p. 405
Directional selection
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น�#น• ต�วอยุ�าง เชั�น ความต&านที่านต�อป็ฏิ�ชั�วนะ
Stabilizing Selection
#
p. 405
Distribution
#
p. 405
Disruptive Selection
#
p. 405
MicroevolutionMutation - source of new variation
Gene Flow - redistributes variation
Genetic Drift - reduces variation (by chance)
Non-random mating - maintains (outbreeding) or reduces (inbreeding) variation
Natural Selection - reduces variation (due to environment)
Hardy-Weinberg Assumptions
NO EVOLUTION
no mutation
population is genetically isolated
very large population size
random mating
no natural selection
Hardy-WeinbergAre the assumptions of Hardy-
Weinberg likely to be met?
Nope.
Why is the equation useful?
Modification by terms for pop. size, selection, non-random mating, etc. more realistically model real populations.
EVOLUTION
mutation
gene flow
genetic drift
assortative mating
natural selection
Hardy-Weinberg Assumptions
Decreasing VariationGenetic Drift - reduces variation (by
chance)
Inbreeding - reduces variation by increasing homozygosity
Natural Selection - reduces variation (due to environment); disadvantaged alleles disappear
Maintaining Variation
Mutation - creates new alleles
Neutral Alleles - do not affect the fitness of an organism; are not removed by natural selection
Subpopulations - selection different in different areas but gene flow keeps them “mixing”
Dislocation of European bison's subpopulations in Ukraine
Maintaining VariationGene Flow through Sexual Reproduction
- new combinations of alleles
Polymorphism - two genotypes favored by selection (often frequency dependent)e.g., right mouthed & left mouthed scale eating fishes
Heterozygote Advantage - heterozygote parents produce some homozygote offspring
Right mouthed & Left mouthed scale eating fishes
conspicuously asymmetrical left-bending (left) and right-bending (right) individuals of the scale-eating cichlid fish Perissodus microlepis from Lake Tanganyika.
(Photo courtesy of A Meyer.)Palmer Journal of Biology 2010 9:11 doi:10.1186/jbiol218
Sickle Cell DiseaseHbnHbn = “normal” red blood cells; no
sickle cell disease
HbnHbs = some sickled red blood cells some normal; mild sickle cell disease and some protection from malaria
HbsHbs = sickled red blood cells; sickle cell disease causing death and some protection from malaria
Sickle Cell Disease In malarial areas:
sickle cell malaria
HbnHbn none highly susceptible
HbnHbs mild low susceptibility
HbsHbs death low susceptibility
Relationship of Phenotype and Genotype
The Genotype codes for the Phenotype
-Almost all enzymes are proteins. -Almost all traits are produced by the action of proteins.
Genotype PhenotypeGenotype and phenotype are not exactly
correlated.
Environment is important.
e.g., human height
Phenotypic plasticity - the production of different phenotypes in response to different environments.
e.g., white oak leaves
• A change in the environment also can affect the phenotype.
• Pinkness in flamingos is not encoded into their genotype.
• The food they eat makes their phenotype white or pink.
Evolutionary ConstraintAll conceivable mutations are not
possible.
The organism must still function.
All jawed vertebrates have a body plan with 2 pairs of paired appendages.
No six legged vertebrates.
Evolution must work with what it has.Major reorganization very rare.
Evolutionary Constraint
p. 411
• Why couldn't terrestrial arthropods evolve to be as large as elephants?
• What is an evolutionary constraint?
The laws of Physics and Inheritance
• Arthropods inherited both an exoskeleton and jointed legs.
• These traits have opened up many opportunities in arthropod evolution, but they have also blocked other possibilities.
• In particular, there are three constraints on the size of terrestrial arthropods: – Molting: Molting is more hazardous for larger animals. – Exoskeleton strength: The exoskeleton may not be
strong enough to support larger animals. – Respiration: Many arthropods can only get enough
oxygen to support small bodies.
The land-dwelling coconut crab weighs in at 5 kg (over 10lbs). For these giants, molting is a serious commitment: they may spend a whole month in a deep burrow wriggling out of the old skin and waiting for the new one to firm up!
crab3[1].swfIs the physics of molting a constraint on arthropod size?
You've just seen that molting out of the exoskeleton may limit the size of terrestrial arthropods. Does the exoskeleton cause other problems for outsized arthropods? To figure out the answer, we'll see what happens to the exoskeleton and the muscles that move it when an arthropod is scaled up.
Exoskeleton strength: Blowing up ants
What would happen to an ant if it were scaled up, keeping all its body parts in proportion? Each ant below is twice the size of the previous one. See what happens when it gets up to go forage for food.
ant_walk2[1].swf
Exoskeleton strength: A solution?
So is there any solution to this problem? Well, wider tubes are stronger than narrower ones. Perhaps if we gave our giant ant extra-wide legs with an extra-thick exoskeleton, it wouldn't suffer so many broken limbs. Does this ant look like it might be a winner?
Extra large means extra heavy
ele_ant_walk[1].swf
The Crustacean/Spider Model
The Insect Model
Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout
the body.
Tracheae and trachioles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells.
The Crustacean/Spider Model
The Insect Model
Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body.
Tracheae and tracheoles (essentially ductwork) allow air to circulate throughout the body — oxygen diffuses into the tissues near individual cells.
The Crustacean/Spider Model
The Insect Model
Water/air passes over gills/book lungs and oxygen diffuses into the blood. The blood carries oxygen throughout the body.
Test.png
Test.png
celltracheae[1].swfgillsbooklungs[1].swf
Respiration: Gotta have oxygen
All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect.
All animals, including insects, need oxygen. Without it, their cells die. Insects don't have lungs and their "blood" doesn't carry oxygen. Insect cells get oxygen via a direct link to the air outside — a network of tubes, called tracheae let oxygen reach cells deep within the insect.
The tubes below represent the tracheae of three dragonflies. In this model, each tube supplies a gut cell with oxygen — the larger the dragonfly, the longer the tube. The blue dots represent oxygen molecules. See how oxygen moves through the tubes. The gut cell in the biggest dragonfly is not doing too well because it is not getting enough oxygen. There is a limit to the length of tracheae (and thus to the size of the dragonfly) that can provide every cell with sufficient oxygen.
dragonfl_air[1].swf
Conclusion• Evolution is an undirected process, constrained
– by physical laws (such as gravity)– by genetics (which might, for example, encode the
directions for building breathing organs in a particular way), and
– by the environment (which might not, for example, contain a niche for a large, slow-moving, and fragile ant).
• In the case of the arthropods, the exoskeleton — a useful adaptation for body support, protection and water retention as well as their respiratory system, may have brought evolutionary constraints along with benefits.
