The Theory of Evolution
Charles Darwin’s Life and Work
Evidence for Evolution
Mechanisms of Evolution
Biology I
Charles Darwin’s Life and Work
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1809-1882
English scientist
At age 21, Darwin took a job as a naturalist on the English ship
HMS Beagle which sailed to South America and the South
Pacific on five-year scientific journey around the world.
Darwin collected and studied biological specimens at every port
along the route, but focused his attention on the unique animals
and plants of the Galapagos Islands.
His studies provided the foundation for his theory of evolution
by natural selection.
The Five-Year Voyage of the HMS Beagle
The Galapagos Islands
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A group of volcanic islands located off the
coast of South America
Home to a variety of unique species
The Unique Creatures of the Galapagos Islands
Natural Selection
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Driving force for
evolution
During the struggle for
resources,the
strongest survive &
reproduce.
Idea that at least
some of the
differences between
individuals, which
impact their survival
and fertility, are
inheritable
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Natural Selection and The Theory of Evolution
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Natural selection is a mechanism for change in
populations that occurs when organisms with certain
variations survive, reproduce, and pass their
variations to the next generation.
Organisms without these variations are less likely to
survive and reproduce. As a result, each generation
consists largely of offspring from parents with these
variations that aid survival.
Darwin published the first book about evolution called
On the Origin of Species by Natural Selection in
1859.
The ideas detailed in Darwin’s book are today’s basic
unifying theme of biology.
Four Principles of Natural Selection
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Variation – individuals in a population differ from one
another due to their genetic make make-up, whether
inherited or from mutations
Overproduction – populations produce more offspring than
can possibly survive and this results in competition among
offspring
Adaptation – certain variations allow individuals to survive
better their environment better than others and to
produce more offspring that share those adaptations for
their environment
Heritability – as long as environmental conditions remain
beneficial for a trait, more individuals will have the trait
over time as it is passed from one generation to the next
Fitness
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A measure of the ability to survive and
produce more offspring relative to
other members of the population in a
given environment
If differences in individual genotypes
affect fitness, then the frequencies of
the genotypes will change over
generations; the genotypes with higher
fitness become more common. This
process is called natural selection.
Artificial Selection
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The process by which human beings change a
species by breeding it for certain traits
Humans act as the selective agent by
determining which traits are favorable and
then breed individual that show those traits
In natural selection, the environment creates
the selective pressure that determines if a
trait is passed on or not
Darwin observed the breeding of pigeons to
study artificial selection and concluded that
the same basic process worked in nature but
required more time and could produce new
species
Common Descent with
Modification
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Darwin proposed
that organisms
descended from
common ancestors
Idea that
organisms change
with time,
diverging from a
common form
Caused evolution
of new species
Phylogeny/Cladistics
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Phylogeny - the evolutionary history for
a group of species
Cladistics – classification based on
common ancestory
Cladogram – evolutionary tree that
proposes how species may be related to
each other through common ancestors;
based on homologous structures
Cladogram of Vertebrate
Chordates
Microevolution
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Observable changes in the allele
frequencies of a population over time
which result in relatively small changes
within the species or population; looks
at effect of mutations and natural
selection on phenotype or form
Examples: pesticide resistance,
herbicide resistance, bacterial
resistance to antibiotics, changes in
color or size within a population
http://www.windows.ucar.edu
/tour/link=/earth/Life/geneti
cs_microevolution.html&edu=e
lem
Macroevolution
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Evolution on a grand scale or above the level
of a population or species
Looks at the over-arching history of life
Evidence for Evolution
Adaptation – any variation that aids an organism’s
chances of survival in its environment
A. Structural Adaptations
1. Mimicry – a structural adaptation that enables one
species to resemble another species
Example 1: The Viceroy butterfly has evolved a very
similar pattern of coloration to the monarch; it is
thought that the Viceroy is acting as a mimic, the
similarity providing some protection from predators,
such as birds, which often mistake the edible Viceroy
for the inedible Monarch.
The Monarch feeds on milkweed and tastes bitter. Potential
predators confuse the Viceroy for the Monarch and avoid eating it.
Example 2: The colors and body shape of a yellow
jacket wasp and a harmless syrphid fly are similar.
Predators avoid both insects. The syrphid fly is on
the left, and the yellow jacket wasp is on the right.
2. Camouflage – a structural adaptation that enables
species to blend with their surroundings; this usually
means that they are not easily found by their
predators and survive to reproduce
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The stick insect on the left blends in almost
unnoticeably with the branch it sits on.
The mottled sand grasshopper on the right is hardly
visible on the wood.
England’s Salt and Pepper Moths
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99+% of population prior to
industrial revolution was light
colored
As coal soot killed lichens on
trees light moths stood out to
predators
Dark form (morph) appeared
and by mid 1900s made up
90+% of population
With pollution control, both
lichens and light moths are
coming back
B. Physiological Adaptations
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1. Resistance
Involve changes in an organism’s metabolic processes
May develop in much less time than structural adaptations
Examples:
 When the antibiotic drug penicillin was discovered about 50 years
ago, it was called a wonder drug because it killed many types of
disease-causing bacteria and saved many lives. Today, penicillin no
longer affects as many species of bacteria because some have
evolved a physiological adaptation to prevent being killed by
penicillin.
Pesticides are poisons
used to kill insects that
are pests in crops,
swamps, backyards, and
homes. Examples are
DDT, now banned in many
countries, and malathion.
These chemical weapons
against insects have
proved to be doubleedged swords. Natural
selection has allowed
those insects with genes
that somehow enable
them to resist the
chemical attack to
survive. And their
offspring inherit the
genes for pesticide
resistance. DDT was
applied worldwide
beginning in the mid
1940’s, and by the early
1950’s DDT would not kill
house flies.
C. Other Evidence for Evolution
1. Fossils – preserved remnants or impressions left by organisms
that lived in the past that help scientists to understand the
overall picture of how a species evolved; remnants of animals
may be buried, leave impressions, and/or have tissue replaced by
harder minerals
2. Anatomy
a. Homologous structures – similar in arrangement or structure but
not in function; viewed as evidence that organisms evolved from
a common ancestor
b. Analogous structures – similar in function but not in structure;
do not indicate a common evolutionary ancestor
c. Vestigial structures – body structures that have no function in
present-day organisms but were probably useful to an ancestor
3. Embryology – Evolutionary biologists compare structures that
appear during the development of different organisms. All of
the different classes of vertebrates show a structures called
gill slits that appear on the side of the throat and all have a tail
as an embryo. As development continues, the differences in the
embryos will increase until you can distinguish among them. The
similarities among the young embryos suggest evolution from a
distant, common ancestor.
4. Biochemistry – Evolutionary relationships among species leave
signs in DNA and proteins; in genes and gene products.
Scientists compare DNA and RNA of different species and use
the results of biochemical studies to help determine the
evolutionary relationships of species. One of the most recently
developed classification systems for organisms is shown in the
phylogenetic tree below and is based on comparisons of DNA and
RNA.
Mechanisms for Evolution
A. Population Genetics – the studies of the complex behavior of
genes in populations of organisms or allele frequencies.
 Populations consist of all the members of a species that live in
an area with each member of that group possessing genes that
characterize the traits of the species, and these genes exist as
pairs of alleles.
 Evolution occurs as a population’s genes and their frequencies
change over time.
 Genetic change is the result of a change in the population’s gene
pool and the allelic frequency.
 A population in which the frequency of alleles remains the same
over generations is said to be in genetic equilibrium and is not
evolving.
 Mechanisms for genetic change include mutations, genetic drift,
and gene flow.
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Mutations – may be caused from environmental factors or may
be spontaneous; may be lethal or may result in a useful variation
allowing the new gene to becomes part of the population’s gene
pool by the process of natural selection
Genetic Drift – genes are lost in small populations due to chance
events; genes carried by the parents might not be passed on to
their offspring; loss of genetic diversity
In this example, the parents carry three different genes for a
particular trait: a, A and B, but they pass only a and A to their
offspring. Gene B is lost due to chance.
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Bottleneck Effect: genetic drift that occurs
after an event greatly reduces the size of a
population
Examples: overhunting of a species leads to a
great reduction in the number of individuals in
the population which reduces the genetic
diversity within that population
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Founder Effect: genetic drift that
occurs after a small number of
individuals colonize a new area; the
genes of these individuals are often
very different from those of the larger
population; common in communities
established by a small number of
immigrants
Example: Tay-Sachs Disease
The Founder Effect
Sexual Selection
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Reproduction can be costly for females as far
as energy is concerned therefore females can
be very choosy about mates.
Sexual selection occurs when certain traits
increase mating success.
Intrasexual selection = male competition
Intersexual selection = males display traits
that attract females; some traits can
become very exaggerated such as red air
sacs in male frigate birds
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Gene Flow – As individuals move in and out of a population by
migrating, the genetic equilibrium is disrupted. When individuals
leave a population, genes are lost from the gene pool, and when
individuals enter a population, their genes are added to the gene
pool.
B. Speciation – The evolution of new species that occurs when
members of similar populations no longer interbreed to produce
fertile offspring within their natural environment.
Speciation can occur due to a number of factors.
1. Geographic isolation – occurs when a physical barrier divides a
population; over time, each small population might adapt to its
environment through natural selection and develop its own gene
pool and result in new species
2. Reproductive isolation – occurs when formerly interbreeding
organisms can no longer mate and produce fertile offspring
 Genetic material of the populations becomes so different that
fertilization cannot occur.
 Behavior may prevent reproduction. Two populations may mate
at different times of the year.
Patterns of Evolution
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Biologists have observed different patterns of evolution that
occur throughout the world in different natural environments.
Divergent Evolution – occurs when species that once were similar
to an ancestral species diverge, or become increasingly distinct
Adaptive radiation – occurs when an ancestral species evolves into
an array of species to fit a number of diverse habitats
Examples – Darwin’s finches of the Galapagos Islands and
Hawaiian Island honeycreeper
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Convergent Evolution – distantly related organisms evolve similar
traits and unrelated species occupy similar environments in
different parts of the world; they share similar pressures of
natural selection due to similar environments
Examples – The Senita cactus of Mexico is similar in appearance
and adaptations to its environment as the Euphorbia from
Madagascar. They both fill a similar niche in the ecosystem of
their respective habitats.
Darwin's Theory
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Individual Organisms In Nature Differ From One
Another. Some Of This Variation Is Inherited.
Organisms In Nature Produce More Offspring Than
Can Survive, And Many Of These Offspring Do Not
Reproduce.
Because More Organisms Are Produced Than Can
Survive, Members Of Each Species Must Compete
For Limited Resources.
Because Each Organism Is Unique, Each Has
Different Advantages & Disadvantages In The
Struggle For Existence.
Individuals Best Suited To Their Environment
Survive & Reproduce Successfully – Passing Their
Traits To Their Offspring.
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Species Change Over Time. Over Long Periods,
Natural Selection Causes Changes That May
Eventually Lead To New Species.
Species Alive Today Have Descended With
Modifications From Species That Lived In The Past.
The Greatest Potential For Evolutionary Change
Occurs When Many Mutations Occur Within A
Small Population.