Transcript What is Evolution??

Major Objectives
1. Understand the historical context for
evolutionary theory, including Darwin's
field research that helped frame his view
of life
2. Define Darwinism and Darwin's main
ideas from the Origin of Species
3. Discuss examples of natural selection
and other evidence for evolution
"Nothing in biology makes sense
except in the light of
evolution."
Theodosius Dobzhansky
What is Evolution??
Change in gene frequency
in a population over time
Evolution was resisted by Western
culture
-Greek philosophers:
Aristole (scala naturae)
-Natural theology (1700's)
Ladder of Life
Lamarkian Evolution
Figure 22.3 Formation of sedimentary rock and deposition of
fossils from different time periods
Figure 22.2 Fossils of trilobites, animals that lived in the seas
hundreds of millions of years ago
Figure 22.4 Strata of sedimentary rock at the Grand Canyon
Galapagos Island Finches:
Beaks Differed According to Food Supply
Darwin's
Intellectual
Revolution
Millions of DNA Switches That Power Human
Genome's Operating System Are Discovered
ScienceDaily (Sep. 5, 2012) — The locations of millions of DNA 'switches'
that dictate how, when, and where in the body different genes turn on and
off have been identified by a research team led by the University of
Washington in Seattle. Genes make up only 2 percent of the human
genome and were easy to spot, but the on/off switches controlling those
genes were encrypted within the remaining 98 percent of the genome.
In the mid-1990s, researchers were surprised to discover that fruit flies, mice, and humans who
were born missing eye structures had defects in the same gene. This gene, called Pax6 (or eyeless
in flies), is required for normal eye development in all animals with bilateral symmetry. Even in eyes
that look very different, Pax6 functions in much the same way. When placed in a fly, the mouse
Pax6 gene activates all the genes necessary to form a normal, functional fly eye (not a mouse eye).
What the Encode project tells us about the
human genome and 'junk
ENCODE, the Encyclopedia of DNA Elements, is the most ambitious human genetics project
to date. It takes the 3 billion letters described by the Human Genome Project in 2000, and
tries to explain them.
http://www.youtube.com/watch?v=Y3
V2thsJ1Wc
http://www.youtube.com/watch?v=UBQ
5a7mCpMs
Darwinism has a dual meaning
-Evolution as the explanation for
life's unity and diversity (descent
with modification)
-Natural selection as the cause of
adaptive evolution
Figure 22.7 Descent with modification
Darwin's main ideas from "The
Origin of Species"
Artificial Selection-selecting
desired traits
1. Natural
selection is
differential
success in
reproduction
Idea of
overreproduction
influenced by
Thomas Malthus
(1798)
1. Differential success in reproduction
Not All Organisms Get To Mate
Why is this important?
2. Natural selection occurs through
an interaction between the
environment and the variability
inherent among the individual
organisms making up a population
Why is this important?
3. The product of natural selection is
the adaptation of populations of
organisms to their environment
How does this result in population change?
How does
natural
selection
work?
Peppered Moths: Real Natural Selection Example
•Original population: white in color, blended into lichens on trees
•During industrial revolution, lichens died & trees covered in soot
•Lighter moths had higher predation rates, darker moths had high survival rates
•Over time, population became dominated by dark moths
Darwin’s Theory of Natural Selection:
Favorable traits that are heritable become more common in
successive generations of a population, and unfavorable traits that
are heritable become less common
If phenotypes have a genetic basis, phenotypes will increase or
decrease in frequency
Results in change in gene frequency over time
Darwin’s Theory Lacked Satisfactory
Theory of Heredity
• Modern Synthesis (1920-1940):
• Unification of Mendel’s theory of heredity and Darwinian evolution
Evidence for Evolution
Evidence for Evolution
Fossil Record
Natural selection
Homologous structures
Molecular Biology-DNA
Islands
Vestigial Organs
Convergent Evolution
Same skeletal elements, different functions
500 endemic species
Vestigial Organs
Convergent Evolution- The
independent development of
similarity between species as
a result of their having similar
ecological roles and selection
pressures
Major Objectives
1. Do populations or organisms evolve?
2. What are the major differences between
microevolution and macroevolution?
3. What are the four main factors that can
alter genetic diversity?
4. Identify the three main modes of natural
selection.
5. Describe the four main reasons why
natural selection cannot produce perfection.
Populations Evolve,
Natural Selection
Occurs at the Level
of Organisms
Types of Evolution
*Microevolution-A change in the gene
pool of a population from generation to
generation
*Macroevolution-Evolutionary change on a
grand scale, encompassing the origin of
new taxonomic groups, evolutionary
trends, adaptive radiation, and mass
extinction
Four Main Factors That
Can Alter Genetic
Diversity
1) Genetic Drift
A change in a population’s genetic
diversity due to chance
Why are small populations so vulnerable
to extinction?
Extinction Vortex
Disturbance lowers population size
Reduced Genetic Variability
Reduced ability to survive environmental stochasticity
Founder Effect—example for higher risk of breast or ovarian cancer in women
Four Main Factors That
Can Alter Genetic
Diversity
1) Genetic Drift
2) Natural Selection
Differential success
in reproduction
Four Main Factors That
Can Alter Genetic
Diversity
1) Genetic Drift
2) Natural Selection
3) Gene Flow
Genetic exchange due to the migration
of fertile individuals between
populations
Four Main Factors That
Can Alter Genetic
Diversity
1) Genetic Drift
2) Natural Selection
3) Gene Flow
4) Mutation An accidental change in an
organism's DNA
Natural Selection Common Misconceptions:
Not Goal-Oriented or Progressive
• Change follows environmental conditions
"Survival of the Fittest"
-Misleading phrase: Does NOT mean
competitiveness contest between
individuals
-Darwinian Fitness: the contribution an
individual makes to the gene pool of the
next generation relative to the
contributions of other individuals
Natural Selection Common Misconceptions:
Is Specific to Environmental Conditions
• Specific phenotype is only adaptive in a specific environment
Natural selection does not produce perfection
soft-shell turtle
1) Evolution is limited by historical constraints
2) Adaptations are often compromises
3) Not all evolution is adaptive
4) Selection can only edit existing variations
All phenotypic variation is NOT heritable
Phenotypes are the result of:
1) inherited genotype 2) environmental influences
Reaction Norms: pattern
of phenotypic expression
of a single genotype
across a range of
environments
Four Main Modes of
Genetic Selection
1) Directional Selection
2) Diversifying/Disruptive Selection
3) Stabilizing Selection
4) Sexual Selection
Directional Selection
Diversifying Selection
Stabilizing Selection
Sexual Selection
Three Main Types of
Speciation
1) Allopatric
Speciation
2) Sympatric
Speciation
3) Parapatric
Speciation
Allopatric
Speciation
Sympatric Speciation
Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates
on the type of fruit they grew up in. So hawthorn flies generally end up mating with other hawthorn flies and
apple flies generally end up mating with other apple flies. This host shift from hawthorns to apples may be the
first step toward sympatric speciation—in fewer than 200 years, some genetic differences between these two
groups of flies have evolved.
Parapatric Speciation
Some of these plants live near mines where the soil has become contaminated with heavy metals. The plants
around the mines have experienced natural selection for genotypes that are tolerant of heavy metals. Meanwhile,
neighboring plants that don't live in polluted soil have not undergone selection for this trait. The two types of plants
are close enough that tolerant and non-tolerant individuals could potentially fertilize each other — so they seem to
meet the first requirement of parapatric speciation, that of a continuous population. However, the two types of
plants have evolved different flowering times. This change could be the first step in cutting off gene flow entirely
between the two groups.
Major Objectives
1. Define the biological species concept and
its limitations
2. Understand prezygotic and postzygotic
barriers that isolate gene pools of biological
species.
Biological Species Concept
A species is a population or group of
populations whose members have the
potential to interbreed with each other in
nature to produce viable, fertile offspring.
Lynx rufus
Lynx canadensis
What about limitations?
*Difficult to test reproductive isolation of
morphologically similar fossils
*Difficult to test reproductive isolation of
morphologically living species
*Doesn't address species that reproduce
asexually (e.g., bacteria)
*Doesn't address hybrids (e.g., plants, zoo
animals)
Habitat Isolation
Land and water garter snakes
Behavioral Isolation
the eastern and western meadowlarks shown below are very similar birds whose habitats overlap
Temporal Isolation
Mechanical Isolation
Gametic Isolation
Sea urchins release gametes at same time and place but they don’t fuse
Reduced Hybrid Viability
In crosses between different species of irises, for example, the embryos die before seeds form.
Reduced Hybrid Fertility
Mules are sterile hybrids formed by mating a female horse with a male donkey.
Hybrid Breakdown
Mating between two F1 hybrids produces a second hybrid generation, this F2 generation may be unable to
reproduce because of hybrid breakdown. The second-generation hybrids are defective in some way that
prevents successful reproduction. Hybrid breakdown has been demonstrated in sunflower hybrids.