Transcript Evolution

Announcements
● Tutoring
Center
SCI I, 407
M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,
Th 8-12, 6-7; F 8-9
● MasteringBiology Assignment due Thursday 5/26
● Parts of Chapters 13 and 14
Evolution
Evolution – genetic change in a population or a species
over generations.
•An understanding of evolution informs every field of
biology, for example:
Agriculture
Medicine
Biotechnology
Conservation biology
Evolution
Darwin made two main points in
The Origin of Species:
• Organisms inhabiting Earth today descended from
ancestral species
• Natural selection was the mechanism for descent with
modification
Observations
Overproduction
of offspring
Individual
variation
Conclusion
Natural selection:
unequal reproductive success
Observing Natural Selection
There are many examples of natural selection in action.
Galápagos finches change beak size depending upon the size and
shape of available seeds.
Natural Selection in Action
Examples of natural selection include:
• Pesticide-resistant insects
• Antibiotic-resistant bacteria
• Drug-resistant strains of HIV
Insecticide application
Chromosome with
gene conferring
resistance to pesticide
Survivors
Reproduction
Evolution
Natural selection leads to:
• A population (a group of individuals of the same
species living in the same place at the same time)
changing over generations
• Evolutionary adaptation A flower mantid in Malaysia
A Trinidad tree mantid
that mimics dead leaves
A leaf mantid in
Costa Rica
Evidence of Evolution
– Biological evolution leaves observable signs.
– We will examine five of the many lines of evidence in
support of evolution:
• The fossil record
• Biogeography
• Comparative anatomy
• Comparative embryology
• Molecular biology
Evidence of Evolution
•The Fossil Record
– Fossils are:
• Imprints or remains of organisms that lived in the past
• Often found in sedimentary rocks
Evidence of Evolution
•Biogeography
– The study of the geographic distribution of species that first
suggested to Darwin that today’s organisms evolved from
ancestral forms.
Common
ringtail
possum
Australia
Koala
Common wombat
Red kangaroo
Evidence of Evolution
•Comparative Anatomy
• Is the comparison of body structure between different species
• Confirms that evolution is a remodeling process
Human
Cat
Whale
Bat
Evidence of Evolution
•Comparative Embryology
– Early stages of development in different animal species reveal
additional homologous relationships.
Pharyngeal
pouches
Post-anal
tail
Chicken embryo
Human embryo
Evidence of Evolution
•Molecular Biology
– The hereditary background of an organism is documented in:
• Its DNA
• The proteins encoded by the DNA
– Evolutionary relationships among species can be determined
by comparing:
• Genes
• Proteins of different organisms
Populations as the Units of Evolution
– A population is:
• A group of individuals of the same species, living
in the same place, at the same time
• The smallest biological unit that can evolve
– Gene pool - The total collection of alleles in a
population at any one time.
– Microevolution - When the relative frequency of
alleles changes over a number of generations,
(evolution is occurring on its smallest scale).
Mechanisms of Evolution
– The main causes of evolutionary change are:
• Genetic drift
• Gene flow
• Natural selection
Mechanisms of Evolution
– Genetic drift is:
• A change in the gene pool of a small population
• Due to chance
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Only 5 of
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leave
offspring
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Only 2 of
10 plants
leave
offspring
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Mechanisms of Evolution
– The bottleneck effect:
• Is an example of genetic drift
• Results from a drastic reduction in population size
Original
population
Bottlenecking
event
Surviving
population
Mechanisms of Evolution
– The founder effect is likely when a few individuals
colonize an isolated habitat and represent genetic drift
in a new colony.
Tristan da
Cunha
South
Africa
America
Mechanisms of Evolution
– Gene flow:
• Is genetic exchange with another population
• Tends to reduce genetic differences between
populations
Outcomes of Natural Selection
Evolved
population
Frequency
of individuals
Original
population
Phenotypes (fur color)
Original
population
(a) Directional
selection
(b) Disruptive
selection
(c) Stabilizing
selection
Mechanisms of Evolution
●Sexual dimorphism is:
A distinction in appearance between males and females
Not directly associated with reproduction or survival
●Sexual selection is a form of natural selection in which
inherited characteristics determine mating preferences.
(a) Sexual dimorphism in
a finch species
(b) Competing for mates
Evolution
Macroevolution:
•Encompasses the major biological changes evident in
the fossil record
•Includes the formation of new species
– Speciation:
• Is the focal point of macroevolution
• May occur based on two contrasting patterns
– In nonbranching evolution:
• A population transforms but
• Does not create a new species
Evolution and Speciation
Speciation:
•Is the focal point of macroevolution
•May occur based on two contrasting patterns
In nonbranching evolution:
•A population transforms but
•Does not create a new species
Nonbranching
Evolution
(no new species)
Branching
Evolution
(results in
speciation)
Biological Species Concept
– Species is a Latin word meaning:
• “Kind” or
• “Appearance.”
– The biological species concept defines a species as
• “A group of populations whose members have the
potential to interbreed and produce fertile
offspring”
Reproductive Barriers between Species
– Prezygotic barriers prevent mating or fertilization
between species.
– Postzygotic barriers operate if:
• Interspecies mating occurs and
• Hybrid zygotes form
Zygote
Gametes Prezygotic barriers
• Temporal isolation
• Habitat isolation
• Behavioral isolation
• Mechanical isolation
• Gametic isolation
Viable,
Postzygotic barriers
fertile
• Reduced hybrid viability offspring
• Reduced hybrid fertility
• Hybrid breakdown
Mechanisms of Speciation
Species can form by:
• Allopatric speciation, due to geographic isolation
• Sympatric speciation, without geographic isolation
Allopatric speciation
Simpatric speciation
Mechanisms of Speciation
Populations
become
allopatric
Populations
become
sympatric Populations
interbreed
Gene pools merge:
No speciation
Geographic
barrier
Time
Populations
cannot
interbreed
Reproductive
isolation:
Speciation has
occurred