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Chapter 1
SCIENCE OF ZOOLOGY AND
EVOLUTION OF ANIMAL DIVERSITY
1-1
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Science of Zoology
• Zoology:
The scientific study of animal life
Phylogeny or phylogenetic tree is a diagram
whose branches represent evolutionary
lineages and depicts the common descent of
species or higher taxa
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Principles of Science
• Nature of science:
– Science is guided by natural law
– Science has to be explained by reference to natural
law
– Science is testable against the observable world
– The conclusions of science are tentative and
therefore not necessarily the final word
– Science is falsifiable
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Principles of Science
• Scientific Method
– Hypothetico-deductive Method:
Scientific process of making a conjecture or
assumption and then seeking empirical tests that
potentially lead to its rejection
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Principles of Science
– Hypothesis:
• Potential answers to questions being asked
• Derived from prior observations of nature or
from theories derived on such observations
• Often constitute general statements about
nature that may explain a large number of
diverse observations
• If a hypothesis is very powerful in explaining a
wide variety of related phenomena, it attains
the level of a theory
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Principles of Science
•
The scientific method may be summarized as
a series of steps:
1.
2.
3.
4.
Observation
Question
Hypothesis Formation
Empirical Test
– Controlled Experiment
Includes at least 2 groups
Test Group
Control Group
5. Conclusions
Accept or reject your hypothesis
6. Publications
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Principles of Science
• Experimental vs. Evolutionary Sciences
– Experimental Sciences:
• Seek to explain the proximate or immediate
causes that underlie the functioning of
biological systems at a particular time and place
• Goal: To explain how animals perform
metabolic, physiological, and behavioral
functions at the molecular, cellular, organismal,
and populational levels
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Principles of Science
– Example:
• How do birds navigate when migrating long
distances?
• What mechanism allows a jellyfish to sting?
• How does population density affect the
physiology and behavior of organisms?
Biological sciences that investigate proximate
causes are called experimental sciences
because they use the experimental method
which includes a control
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Principles of Science
– Example:
Studying processes by which animals maintain their body
temperature under different environmental conditions,
digest food, migrate to new habitats, or store energy
Experimental sciences:
Molecular biology, cell biology, endocrinology,
immunology, physiology, developmental
biology, and community ecology
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Principles of Science
Evolutionary Sciences: addresses questions of
ultimate causes that have molded biological
systems and their properties through
evolutionary time
– Example:
• Why do different species of animals have
different numbers of chromosomes in their
cells?
• Why do some animal species maintain complex
social systems, whereas other species have solitary
individuals?
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Principles of Science
• Evolutionary sciences require comparative
method rather than just experimentation.
• Systematics is the ordering of organism
according to their inferred evolutionary
relationships for comparative study.
• Evolutionary Sciences:
Comparative Biochemistry, Molecular
Evolution, Comparative Cell Biology,
Comparative Anatomy, Comparative
Physiology, and Phylogenetic Systematics
1-12
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1-13
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Origins of Darwinian Evolutionary Theory
• Pre-Darwinian Evolutionary Ideas
– Early Greek philosophers, Xenophanes,
Empedocles, and Aristotle
• Developed idea of evolutionary change
– Recognized fossils as evidence of former life
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Origins of Darwinian Evolutionary Theory
• Lamarckism: The First Scientific Explanation of
Evolution
– Jean Baptiste de Lamarck (1744 – 1829)
• Authored 1st complete explanation of evolution in
1809
• Made convincing case that fossils were remains of
extinct animals
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Origins of Darwinian Evolutionary Theory
• Proposed an evolutionary mechanism
– Inheritance of acquired characteristics
»Organisms strive to meet demands of the
environment
»Acquire adaptations and pass them by
heredity to offspring
»Individual organisms transform their
characteristics to produce evolution
• This hypothesis was rejected.
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Origins of Darwinian Evolutionary Theory
• Darwin’s evolutionary theory
– Differs from Lamarck's in being a variational not a
transfromational theory
– Evolutionary change is caused by differential
survival and reproduction among organisms
differing in hereditary traits
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Origins of Darwinian Evolutionary Theory
• Charles Lyell and Uniformitarianism
– Sir Charles Lyell (1797-1875)
• Geologist
• Principle of Uniformitarianism
–Guides scientific study of the history of
nature
–Laws of physics and chemistry have not
changed throughout earth’s history
–Past geological events occurred by natural
processes similar to those observed today
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1-20
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Origins of Darwinian Evolutionary Theory
• Lyell’s studies led him to conclude that the
earth’s age must be measured in millions of
years
–Claims left important marks on Darwin’s
evolutionary theory
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Origins of Darwinian Evolutionary Theory
• Darwin’s Great Voyage of Discovery
– Charles Robert Darwin
• Presented the first credible explanation of
evolutionary change
• Made extensive collections and observations
on a 5 year voyage (1831-1836) on the H.M.S
Beagle
• Published his findings in On the Origin of
Species by Means of Natural Selection in 1859
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1-23
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1-24
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1-25
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Theories of Evolution and Heredity
•
Ernst Mayr (Harvard University) proposed
that Darwinism should be viewed as five
major theories:
1.
2.
3.
4.
5.
Perpetual Change
Common Descent
Multiplication of the Species
Gradualism
Natural Selection
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Theories of Evolution and Heredity
• Perpetual Change
The living world is neither constant nor perpetually
cycling, but is always changing
– The varying forms of organisms undergo
measurable change across generations throughout
time
– Documented by the fossil record
– Theory upon which the remaining 4 are based
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Theories of Evolution and Heredity
• Common Descent
All forms of life descend from a common
ancestor through a branching of lineages
– Life’s history has the structure of a branching
evolutionary tree, known as a phylogeny
– Serves as the basis for our taxonomic classification
of animals
1-28
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1-29
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Theories of Evolution and Heredity
•
Multiplication of Species
The evolutionary process produces new species
by splitting and transforming older ones
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Theories of Evolution and Heredity
• Gradualism
Large differences in anatomic traits that
characterize disparate species originate through
the accumulation of many small incremental
changes over very long periods of time
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Theories of Evolution and Heredity
• Natural Selection
A creative process that generates novel
forms from the small individual variations that occur
among organisms within a population
– Adaptation
An anatomical structure, physiological process,
or behavioral trait that evolved by natural
selection and improves an organism’s ability to
survive and leave descendants
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Evidence for Darwin’s Five Theories of Evolution
• Perpetual Change
– Evidenced by the fossil record
• Fossil: remnant of past life uncovered from the
crust of the earth
– Many organisms left no fossils
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Figure 1_10a
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Figure 1_10b
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Figure 1_10c
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Evidence for Darwin’s Five Theories of Evolution
– Interpreting the Fossil Record
• The fossil record is biased because preservation
is selective
–Vertebrate skeletons and invertebrates with
shells provide more records
–Soft-bodied animals leave fossils only in
exceptional conditions
• Fossils form in stratified layers
–New deposits are on top of older material
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1-38
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Evidence for Darwin’s Five Theories of Evolution
– “Index” or “guide” fossils are “indicators” of
specific geological periods
– Layers often tilt and crack, and can erode or be
covered with new deposits
– Under heat and pressure, rock becomes
metamorphic and fossils are destroyed
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1-40
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Evidence for Darwin’s Five Theories of Evolution
• Geological Time
– Sedimentary Rock Layers
– The Law of Stratigraphy
• Dates oldest layers at the bottom and youngest at the
top
• Time is divided into eons, eras, periods and epochs
– Radiometric Dating (late 1940s)
• Method for determining the age of rocks
• Radioactive decay of naturally occurring elements is
independent of heat and pressure
1-41
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Evidence for Darwin’s Five Theories of Evolution
– Evolutionary Trends
• Trends are directional changes in features and
diversity of organisms
• Fossil record allows observation of evolutionary
change over broad periods of time.
• Animals species arise and become repeatedly
extinct.
– Animal species typically survive 1–10 million years
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Evidence for Darwin’s Five Theories of Evolution
• Horse evolution shows clear trend
– Change occurred in both features of horses and
numbers of species
• Trends in fossil diversity are due to different
rates of species formation and extinction
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1-44
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Evidence for Darwin’s Five Theories of Evolution
• Common Descent
– Darwin proposed that all plants and animals
descended from a common ancestor
– Life’s history forms a branching tree called a
phylogeny
– All forms of life, including extinct branches,
connect to this tree
– Phylogenetic research is successful at
reconstructing the history of life
1-45
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Evidence for Darwin’s Five Theories of Evolution
– Homology and Phylogenetic Reconstruction
• Darwin saw homology as major evidence for
common descent
• Richard Owen described homology as “the same
organ in different organisms under every variety
of form and function”
• Vertebrate limbs show the same basic structures
modified for different functions
• Darwin’s central idea that apes and humans have
a common ancestor was explained by anatomical
homologies
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1-47
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Evidence for Darwin’s Five Theories of Evolution
• Branches of the tree combine species into
–Nested hierarchies of groups within groups
• The pattern of nested hierarchies
–Forms the basis for classification of all forms of
life
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Evidence for Darwin’s Five Theories of Evolution
– Ontogeny, Phylogeny, and Recapitulation
• Ontogeny
–History of the development of an organism
through its entire life
• Recapitulation (biogenetic law)
–Ontogeny recapitulates phylogeny
–Flawed notion
–Based on Lamarck’s concept of the
inheritance of acquired traits
1-49
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1-50
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Evidence for Darwin’s Five Theories of Evolution
• Heterochrony
–Evolutionary change in timing of
development
»Characteristics can be added late in
development and features are then
moved to an earlier stage
»Ontogeny can be shortened or
lengthened in evolution
»Leads to mosaic of different kinds of
developmental evolutionary change in a
single lineage
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Evidence for Darwin’s Five Theories of Evolution
• Multiplication of Species
– A branch point in the evolutionary tree occurs
where an ancestral species splits into two
different species
• Total number of species increases in time
• Most species eventually become extinct
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Evidence for Darwin’s Five Theories of Evolution
– Definition of species varies and may include
several criteria
• Members descend from a common ancestral
population
• Interbreeding occurs within a species but not
among different species
• Genotype and phenotype within a species is
similar
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Evidence for Darwin’s Five Theories of Evolution
– Reproductive Barriers
• Central to forming new species
• If diverging populations reunite, before they are
isolated, interbreeding maintains one species
• Evolution of diverging populations requires
they be kept physically separate for a long time
• Geographical isolation with gradual divergence
provides chance for reproductive barriers to
form
1-54
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Evidence for Darwin’s Five Theories of Evolution
– Allopatric Speciation
• Allopatric populations occupy separate
geographical areas
• Cannot interbreed because they are separated,
but could do so if barriers were removed
• Separated populations evolve independently
and adapt to different environments
• Eventually they become distinct enough they
cannot interbreed when reunited
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Evidence for Darwin’s Five Theories of Evolution
• Sympatric Speciation
–Hypothesis that individuals can speciate
while living in different components of the
environment
–Individuals within a species become
specialized for occupying different
components of the environment
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Evidence for Darwin’s Five Theories of Evolution
–Adaptive Radiation
• Evolution of several ecologically diverse species from a
common ancestral species
• Galapagos finches clearly illustrate adaptive radiation
on an oceanic archipelago
1-57
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1-58
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1-59
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Evidence for Darwin’s Five Theories of Evolution
• Gradualism
– Darwin’s theory of gradualism
• Based on accumulation of small changes over
time
– Agreed with Lyell that past changes do not depend
on catastrophic events not seen today
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Evidence for Darwin’s Five Theories of Evolution
– In natural populations
• Usually observe small, continuous changes in
phenotypes
• Under such conditions, major differences
among species would require thousands to
millions of years
• Accumulation of quantitative changes leads to
qualitative change
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1-62
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Evidence for Darwin’s Five Theories of Evolution
• Phyletic Gradualism
–Expect to find in fossil record a long series of
intermediate forms bridging phenotypes of
ancestral and descendant populations
– Niles Eldridge and Stephen Jay Gould proposed
punctuated equilibrium
• Explanation for the discontinuous evolutionary
changes observed through geological time
• Theory that phenotypic evolution is
concentrated in brief events of speciation
followed by long intervals of morphological
evolutionary stasis
1-63
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1-64
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Evidence for Darwin’s Five Theories of Evolution
– Speciation is an episodic event
• Duration of 10,000 to 100,000 years
• Species survive for 5–10 million years
• Speciation may account for less than 1% of
species life span
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Evidence for Darwin’s Five Theories of Evolution
• Natural Selection
– Natural selection provides a natural explanation
for origins of adaptation
– Rapid evolution by natural selection of industrial
melanism in the peppered moths of England
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Figure 1_27
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Revisions of Darwin’s Theory
• Neo-Darwinism
– Darwin:
• Did not know the mechanism of inheritance
• Saw inheritance as a blending of parental traits
• Believed an organism could alter its heredity
through use and disuse of parts
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Revisions of Darwin’s Theory
– August Weismann’s experiments showed an
organism could not modify its heredity
– Neo-Darwinism
• Darwin’s theory as revised by Weismann
– Genetic basis of neo-Darwinism eventually
became what is now called the chromosomal
theory of inheritance
1-70
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Revisions of Darwin’s Theory
• Emergence of Modern Darwinism: The Synthetic
Theory
– In the 1930s geneticists reevaluated Darwin’s
theory mathematically
• Population geneticists
– A new comprehensive theory emerged
• Tied together population genetics,
paleontology, biogeography, embryology,
systematics and animal behavior
1-71
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Revisions of Darwin’s Theory
– Population Genetics
• Studies evolution as change in gene frequencies in
populations
– Microevolution
• Evolutionary changes in frequencies of different allelic
forms of genes
– Macroevolution
• Evolution on a grand scale
• Origins of new structures and designs, trends, mass
extinctions, etc.
– The synthesis theory combines micro- and
macroevolution and expands Darwinian theory
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Microevolution: Genetic Variation and Change
Within Species
• Gene Pool
– Polymorphism
• Different allelic forms of a gene constitute
– Gene pool
• All alleles of all genes that exist in a population
– Allelic frequency
• Frequency of a particular allelic form in a population
• Since each person carries two alleles
– Total numbers of alleles is twice the population size
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Microevolution: Genetic Variation and Change
Within Species
• Genetic Equilibrium
– Whether a gene is dominant or recessive does not
affect its frequency
• Dominant genes do not supplant recessive genes
– Hardy-Weinberg equilibrium
• In large two-parent populations, genotypic ratios
remain in balance unless disturbed
• Accounts for the persistence of rare traits caused by
recessive alleles
– Albinism and Cystic Fibrosis
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Microevolution: Genetic Variation and Change
Within Species
Genotype frequency can be calculated by expanding
the binomial (p - q)2 where p and q are allele
frequencies
• Ex:
• An albino is homozygous recessive
– Trait is represented by q2 in the formula: p2 + 2pq
+ q2 = 1
• Albinos occur in one in 20,000
– q2 = 1/20,000 and q = 1/141
• Non-albino, p, is 1 - q = 140/141
• Carriers would be 2pq
– 2 x 140/141 x 1/141 = 1/70
– One person in 70 is a carrier.
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Microevolution: Genetic Variation and Change
Within Species
– Eliminating a “bad” recessive allele is nearly
impossible
– Selection can only act when it is expressed
• Recessive allele will persist through
heterozygous carriers
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Microevolution: Genetic Variation and Change
Within Species
• How Genetic Equilibrium is Upset
– In natural populations, Hardy-Weinberg
equilibrium is disturbed by 1 or more of 5 factors
• Genetic Drift
– Small populations do not contain large amounts of
genetic variation
– Each individual
• Contains at most 2 alleles at a single locus
– Mating pair
• Maximum of 4 alleles to contribute for a trait
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Microevolution: Genetic Variation and Change
Within Species
– By chance alone, 1 or 2 of the alleles may not be
passed on
– Genetic Drift
• Chance fluctuation from generation to
generation, including loss of alleles
• The smaller the population, the greater the
effect of drift
• Response to change is restricted.
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Microevolution: Genetic Variation and Change
Within Species
• Bottlenecks
–Large reduction in population size leading to
increased significance of genetic drift
– Associated with the formation of a new
geographic population, founder effects
–May lead to speciation
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Microevolution: Genetic Variation and Change
Within Species
• Nonrandom Mating
– If two alleles are equally frequent
• ½ of the population will be heterozygous and ¼
will be homozygous for each allele.
– Positive Assortative Mating
• Individuals mate with others of the same
genotype.
• Increases homozygous genotypes
• Decreases heterozygous genotypes
• Affects 1 or a few traits
• Does not change allelic frequencies
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Microevolution: Genetic Variation and Change
Within Species
– Inbreeding
• Preferential mating among close relatives
• Increases homozygosity
• Affects all variable traits
• Increases the chance that recessive alleles will be
expressed
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Microevolution: Genetic Variation and Change
Within Species
• Migration
– Prevents different populations from diverging
– If a large species is divided into many small
populations
• Genetic drift and selection acting separately in the
different populations can produce evolutionary
divergence among them
• Small amount of migration each generation prevents the
different populations from becoming too distinct
genetically
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Microevolution: Genetic Variation and Change
Within Species
• Natural Selection
– Changes both allelic frequencies and genotypic
frequencies
– An organism that possesses a superior combination
of traits is favored
– Sexual selection
• Selection for traits that obtain a mate but not for survival
– Environmental change alters selective value of traits
• Makes fitness a complex problem
1-85
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1-86
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Microevolution: Genetic Variation and Change
Within Species
• Selection acting on quantitative traits produces 3
evolutionary responses
• Stabilizing selection
–Selects against extreme phenotypes
• Directional selection
–Phenotypic character shifts in one direction
• Disruptive selection
–Selects against average phenotypes
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1-88
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Microevolution: Genetic Variation and Change
Within Species
• Interactions of Selection, Drift and Migration
• Subdivision of a species into small populations that
exchange migrants
– Promotes rapid evolution
• Genetic drift and Selection
– Allow many combinations of many genes to be tested
• Migration
– Allows favorable new combinations to spread
• Interactions of all factors
– Produce change different from what would result from one
alone
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Macroevolution: Major Evolutionary Events
• Speciation and Extinction Through Geological
Time
– A species has two possible fates
• Become extinct or
• Give rise to new species
– Speciation and extinction rates vary among
species
– Lineages with high speciation and low extinction
• Produce the greatest diversity
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Macroevolution: Major Evolutionary Events
• Species Selection
– Differential survival and multiplication of species
based on variation among lineages
– Species-level properties include mating rituals,
social structuring, migration patterns, geographic
distribution, etc.
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Macroevolution: Major Evolutionary Events
• Mass Extinction
– Periodic events where huge numbers of taxa go
extinct
– Mass extinctions appear to occur at intervals of 26
million years.
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Macroevolution: Major Evolutionary Events
• The Permian Extinction
–225 million years ago
–Half of the families of shallow water
invertebrates and 90% of marine
invertebrates disappeared
• The Cretaceous Extinction
–65 million years ago
–Marked the end of the dinosaurs and many
other taxa
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Macroevolution: Major Evolutionary Events
– Catastrophic species selection would result from
selection by these events
• Mammals were able to use resources due to
dinosaur extinction
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