Adaptations
Are inherited characteristics that
enhance an organisms ability to survive
and reproduce in a particular
environment.
 These adaptations evolve.
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The Blue-Footed Booby
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Large, webbed feet
for swimming fast.
Stream-lined body
and bill minimizes
friction when it dives.
Specialized glands
manage salt intake.
Very clumsy and
awkward on land
Chapters on Evolution
We will begin our study of evolution, the
core theme of biology
 We will trace Darwin’s ideas on the origin
of new species.
 We will look at the evolutionary milestones
in the long history of life on Earth and the
mechanisms by which they occurred.
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EVOLUTIONARY THEORY
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The variety of living things on our planet is known as
biological diversity.
How did all of these different organisms arise?
How are they related?
What scientific explanation can account for the
diversity of life?
A collection of scientific facts, observations, and
hypotheses known as the Evolutionary Theory

Evolution:
 change over time;
 the process by which modern organisms have
descended from ancient organisms.
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Theory:
 a well supported, testable explanation of phenomena
that have occurred in the natural world.
The Puzzle of Life’s Diversity
OBJECTIVE:
Describe the pattern Darwin observed among
organisms of the Galapagos Islands.
• Charles Darwin
• 1809 -1882
• In 1831 he was a 22 year
old naturalist.
• Took a 5 year scientific
journey around the world
aboard the HMS Beagle
• He collected and studied
biological and fossil
specimens.
• This served as the
foundation for his theory
of evolution by natural
selection
Darwin in the Galapagos
• What did he Observe?
Plants and animals that were
unique to the island but similar
to species elsewhere
• He considered the possibility
that: Species change over time!
Galapagos finches are
adapted to feed on cacti.
Galapagos tortoises are
the largest on Earth!
Galapagos marine
iguanas eat algae from
the ocean; large claws
help them grip rocks.
Darwin’s Theory of Evolution:

Earth’s many species are descendants
of ancestral organisms that were
different from those living today.
• Evolution~ the change in populations over time.
Section 1: Natural Selection & the Evidence for
• It explains the diversity of species and predicts
Evolution
changes.
Descent with ModificationIs what Darwin called his theory.
 He wrote about the evolutionary
history of life in his book, The Origin
of Species by Natural Selection.
 It explains that all of life is connected
by common ancestry and that
descendents have accumulated
adaptations to changing
environments over vast spans of
time.
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Natural Selection
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Natural Selection is Darwin’s
proposed mechanism for
descent with modification.
 Individuals well suited to the
environment tend to leave more
offspring.
 Over time, favorable traits
accumulate in the population.
How do species change over time?
1. Produce more offspring than can survive
2. Individuals within the population have variations
3. Individuals with useful variations survive,
reproduce, and pass on those traits.
4. Over time, offspring with these traits make up
most of the population.
The Three Key Points of
Evolution by Natural Selection
1.
Individuals DO NOT evolve
1. Evolution refers to generation-to-generation
changes in populations.
Population- a group of individuals of the same
species living in the same place at the
same time.
Evolution by Natural Selection:
Second Point
2.
Acquired traits CANNOT be passed
onto offspring.
2. Natural selection can only amplify or
diminish HERITABLE traits.
For example, a baby will not be born with
biceps of steel just because his father is a
professional weightlifter.
Evolution by Natural Selection:
Third Point
3.
Evolution is NOT goal-oriented
It does NOT lead to perfectly adapted
organisms.
3. Natural selection is the result of
environmental factors that vary from place
to place and from time to time.
For example, a trait that is favorable in one
situation may be useless or even hurtful in
different circumstances.
Darwin continues his studies…
• Thomas Mathus stated that the human
population grows faster than the Earth’s
food supply.
• How did this help Darwin?
• He realized that individuals struggle to
compete in changing environmental
conditions.
• Only some survive and reproduce.
• “Survival of the fittest”
Natural Selection~
A mechanism for change in
populations.
Occurs when organisms with favorable conditions
survive, reproduce, and pass their variations to the
next generation.
Natural Selection = Survival of the fittest =
Struggle for existence
Fitness
Reproductive success is generally more
subtle and passive.
 It has to do with fitness.
 The fittest individuals are those that
produce the largest number of viable,
fertile offspring and therefore, pass the
most genes to the next generation.
 As a result of natural selection,
favorable traits increase in a population.
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Natural selection leads to adaptation, but the
process doesn’t involve “trying.” Natural selection
involves genetic variation and selection among
variants present in a population. Either an individual
has genes that are good enough to survive and
reproduce, or it does not—but it can’t get the right
genes by “trying.”
Outcomes of Natural Selection

Evolutionary fitness is related to genes, but
it’s an organisms phenotypes that is directly
exposed to the environment.
 i.e. physical traits, metabolism, and behavior
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There are three modes of natural selection:
 Stabilizing
 Directional
 Disruptive
Stabilizing selection
The most common mode.
 Favors intermediate
phenotypes.
 Occurs in relatively stable
environments
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 Ex: Human birth weights range
from 6.5-9 pounds; infant
mortality rates may be greater for
babies that are a lot smaller or
larger than this size
Directional Selection
Shifts the overall makeup of
the population by acting
against individuals at one of
the phenotypic extremes.
 Most common during
environmental changes or
when members of a species
migrate to a new habitat with
different environmental
conditions.
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 Ex: Antibiotic resistance in
bacteria resulting from excessive
or incorrect use of antibiotics.
Disruptive Selection
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Occurs when
environmental conditions
are varied in a way that
favors individuals at
BOTH extremes of a
phenotypic range.
Sexual SelectionForm of natural selection in which
individuals with certain characteristics are
more likely than others to obtain mates.
 This can give individuals an advantage in
mating.
 Leads to the evolution of secondary sex
characteristics.
 Results in sexual dimorphismdistinction in appearance of males and
females.
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Evidence of Evolution
Natural selection has been observed in
populations of birds, insects, and many
other organisms. EX: peppered moths
 The fossil record reveals the historical
sequence in which organisms have
evolved.
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 Many fossils link ancestral species with those
living today.
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Biogeography, comparative anatomy, &
molecular biology provide even more
evidence.
 Homologous structures and DNA sequences.
Peppered Moth and the Industrial
Revolution
Fossil Record Evidence

Fossils can reveal when and how fast
organisms appeared, evolved, and
became extinct.
Comparative Anatomy
Homologous structuresfeatures that often have different functions but
are structurally similar because of common
ancestry.
 Ex: Vertebrate forelimbs.
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Evidence continued…
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Vestigial structurestructures that are of marginal or
perhaps no importance to the organism
 Remnant structures that served important
functions in the organism’s ancestors.
Molecular Biology
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Similar genes, DNA sequences, or
proteins amongst diverse organisms
have led to hypotheses about the major
branches on the evolutionary tree of life
Evolutionary Trees
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A branching diagram
that reflects the
evolutionary
relationships among
groups of organisms.
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It’s based on similarities
in characteristics
(homologies) that result
from common ancestry.
The Evolution of Populations
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Gene pool- the total collection of
genes in a population at any one
given time
 It consists of all alleles in all the
individuals making up a population.
(allele frequency)
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Microevolution- a change in a
populations gene pool over a
number of generations
Detecting Microevolutionary Change
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We’ve defined microevolution as a
change in gene frequency in a
population and a population as a group
of organisms that share a common gene
pool—like all the individuals of one
beetle species living on a particular
mountaintop.
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Imagine that you go to the mountaintop this year,
sample these beetles, and determine that 80% of the
genes in the population are for green coloration and
20% of them are for brown coloration.
You go back the next year, repeat the procedure, and
find a new ratio: 60% green genes to 40% brown
genes.
You have detected a microevolutionary pattern:
a change in gene frequency. A change in gene
frequency over time means that the population has
evolved!!
Genetic Variation
Is necessary for a population
to evolve.
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Is generated by mutation and
sexual reproduction.
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Mutation- a change in
nucleotides sequence of
DNA
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Is the ultimate source of
genetic variation
 EX: Bed Bugs &
Pesticide Resistance
Genetic Variation continued…
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Shuffling of alleles in a population that reproduces
sexually.
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Independent orientation of homologous
chromosomes during metaphase I of meiosis
random fertilization
crossing over
ALL of these result in unique combinations of alleles
Genetic variation alone does not guarantee
that microevolution will occur.
Hardy-Weinberg Equilibrium
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States that the allele and genotype
frequencies of a population will remain
constant only if the following conditions are
met:
 Very large population.
 No gene flow between populations.
 No mutations.
 Random mating.
 No natural selection.
Hardy-Weinberg Equation
Public health scientists use this equation to
estimate how many people carry alleles for
certain inherited diseases.
p+q=1
p dominant allele
q recessive allele
 p2 + 2pq + q2 = 1
p2  homozygous dominant
2pq  heterozygous dominant
q2  homozygous recessive
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Mechanisms of Microevolution
Deviations from Hardy-Weinberg equilibrium can
cause changes in gene pools (microevolution)
 Mutation-but they are very random and rare
 Migration*
 Genetic drift *
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 Bottleneck effect
 Founder effect
Natural selection*
 (*)The three main causes of evolutionary change
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Microevolution by Natural
Selection
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Reproductive success of individuals best
suited to the environment.
Natural selection: Beetles with brown genes escaped
predation and survived to reproduce more frequently than
beetles with green genes, so that more brown genes got
into the next generation.
Microevolution by Genetic Drift
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Change in a gene pool due to chance.
 The smaller the population the greater the impact.
 It reduces genetic variation when alleles are lost.
Genetic drift: When the beetles
reproduced, just by random luck
more brown genes than green
genes ended up in the offspring. In
the diagram at right, brown genes
occur slightly more frequently in
the offspring (29%) than in the
parent generation (25%).
Genetic Drift continued…
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Two situations that lead to genetic drift:
 Bottleneck effect
 Founder effect
Bottleneck Effect
Drastic reduction in population size and
change in allele frequencies.
 Due to earthquakes, floods, fires, and
other catastrophes.
 Humans are causing
reduced genetic
variation for other
species because our
actions create severe
bottlenecks.
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Founder Effect
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Differences in the gene pool of a small
colony compared with the original
population.
Natural Selection by Gene Flow
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One of two ways:
 Movement of fertile individuals between populations.
 Transfer of gametes (i.e. pollen) between populations.
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Result:
 gain or loss of alleles
 Reduces differences between populations.
Migration (or gene flow): Some
beetles with brown genes immigrated
from another population, or some
beetles carrying green genes
emigrated.
Adaptive Radiation
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Of all the causes of microevolution, only
natural selection leads to adaptive
radiation Evolution that results in a better fit between
organisms and their environment.
 It is a continuous, dynamic process because
of changing environments.
0-40 mph in 3 strides…
Perfect organisms?
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Natural selection leads to adaptations but not
perfection. Why?
Selection favors the fittest variations from the
available phenotypes, which may not be ideal.
Evolution does not scrap ancestral anatomy; it
co-opts existing structures and adapts them to
new situations.
Adaptations are often compromises. What
benefits an organism in one situation may be
detrimental in another.
Chance, natural selection, and environment
interact.