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1) How old is the earth?
2) What is evolution?
3) How do you think all the species present on
the earth got here?
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Comparative morphologists
study body plans and structures
among groups of organisms
 Some organisms are outwardly
similar, but different internally;
others differ outwardly, but have
similar internal structures
 Some organisms have vestigial
parts with no apparent function
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By the 1800s, many scholars realized
that life on Earth had changed over
time
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Catastrophism
 Georges Cuvier proposed that many
species that once existed became
extinct due to catastrophic geological
events unlike those known today.
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Born in England – 1809
Sailed on the HMS Beagle’s five-year voyage
mapping the coastline of South America.
 Observed and recorded characteristics of species
on the trip
 Developed a scientific theory of biological evolution
- explains how modern organisms evolved over long
periods of time through descent from common
ancestors.
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Wrote On the Origin of Species
Darwin's Finches
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Species vary globally
Species vary locally
 different, yet related, animal species often
occupied different habitats within a local area
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Species vary over time
 Different, yet ecologically similar, animal species
inhabited separated, but ecologically similar,
habitats around the globe
▪ found flightless, ground-dwelling birds that were similar
on different continents.
▪ South America = rheas
▪ Africa = ostriches
▪ Australia = emu.
 Different, yet related, animal species often occupied
different habitats within a local area
▪ Galapagos Islands – the shape of the tortoises’ shells
corresponds to different habitats.
▪ Isabela Island has high peaks, is rainy, and has abundant vegetation
that is close to the ground. A tortoise from Isabela Island has a
dome-shaped shell and short neck.
▪ Hood Island, in contrast, is flat, dry, and has sparse vegetation.
A long neck and a shell that is curved and open around the neck and
legs allow the Hood Island tortoise to reach sparse, high vegetation.
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Darwin collected fossils = the preserved
remains or traces of ancient organisms.
Darwin noticed that some fossils of extinct
animals were similar to living species.
 He discovered fossils of Glyptodont
where armadillos currently live.
▪ Why did Glyptodont disappear?
▪ Why did they resemble armadillos?
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Hutton and Lyell - geologists
 The earth is extremely old
 Processes that changed the past are the same
that operate in the present
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Lamarck – Although his ideas were
FLAWED they shaped Darwin’s
thinking
 Organisms could change during their
lifetimes by selectively using or not using
various parts of their bodies
 Individuals could pass these acquired
traits on to their offspring, enabling
species to change over time.
 Organisms have an inborn urge to
become more complex and perfect, and
to change and acquire features that help
them live more successfully in their
environments.
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Malthus = if the human population grew
unchecked, there wouldn’t be enough living
space and food for everyone
▪ War, famine and disease would work against population
growth
 Darwin realized that most organisms don’t
survive and reproduce, he wondered which
individuals survive…and why?
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Natural selection
 Differential survival and reproduction among
individuals of a population that vary in details of
shared, inherited traits
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Adaptive trait
 Any trait that enhances an individual’s fitness
(ability to survive and reproduce in a particular
environment)
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Natural selection = the process by which
organisms with variations most suited to
their environment survive and leave more
offspring
Natural selection occurs when there is
 1) A struggle for existence – more offspring are
produced than can survive
 2) Variation and adaptation
 3) Survival of the fittest
 Grasshoppers can lay more than 200 eggs at a
time, but only a small fraction of these offspring
survive to reproduce.
 Adaptation = heritable characteristic that
increases an organism’s ability to survive and
reproduce in its environment
▪ EX. Green color is an adaptation: The green
grasshoppers blend into their environment and so are
less visible to predators.
 Fitness = the ability of an organism to survive
and reproduce
▪ Because their color serves as a camouflage adaptation,
green grasshoppers have higher fitness and so survive
and reproduce more often than yellow grasshoppers
do.
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Green grasshoppers become more
common than yellow grasshoppers in this
population over time.
 More grasshoppers are born than can survive
 Individuals vary in color and color is a
heritable trait
 Green grasshoppers have higher fitness in
this particular environment
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Natural selection does not make organisms
“better”.
It is a process that enables organisms to
survive and reproduce in a local environment.
If local environmental conditions change,
some traits that were once adaptive may no
longer be useful
Salamander Evolution
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Evolution starts with mutations in individuals;
mutation is the source of new alleles
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Sexual reproduction can quickly spread a
mutation through a population
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Population
 Individuals of the same species in the same area
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All individuals of a species share certain traits
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Individuals of a population vary in the details
of their shared traits
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Gene pool
 All genes found in one population
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Alleles
 Different forms of the same gene
 Determine genotype and phenotype
 Dimorphism (2 alleles) and polymorphism (many
alleles)
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Mutations are the source of new alleles that
give rise to differences in details of shared
traits
 Lethal mutations usually result in death
 Neutral mutations have no effect on survival or
reproduction
 Beneficial mutations convey an advantage
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Allele frequencies
 Relative abundance of alleles of a given gene in a
population
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Natural populations are never in genetic
equilibrium
 A theoretical state which occurs when a population
is not evolving
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Four processes of microevolution (small-scale
changes in a population's allele frequencies)
prevent genetic equilibrium
 Mutation
 Natural selection
 Genetic drift
 Gene flow
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Five conditions required for a stable gene
pool:
 Mutations do not occur
 Population is infinitely large
 No gene flow
 Random mating
 All individuals survive and reproduce equally
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The Hardy-Weinberg formula can be used to
determine if a population is in genetic
equilibrium
p2(AA) + 2pq (Aa) +q2(aa) = 1.0
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The frequency of the dominant allele (A) plus
the recessive allele (a) equals 1.0
p + q = 1.0
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The number of phenotypes produced for a trait
depends on how many genes control the trait.
 A single-gene trait is a trait controlled by only one gene
▪ Single-gene traits may have just two or three distinct phenotypes.
 Polygenic traits are traits controlled by two or more
genes.
▪ A single polygenic trait often has many possible genotypes and
even more different phenotypes.
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Directional selection
 Changing environmental
conditions can shift
allele frequencies in a
consistent direction
 Forms of traits at one
end of a range of
phenotypic variation
become more common
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Light color is adaptive in areas of low
pollution; dark color is adaptive in areas of
high pollution
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In rock-pocket mice, two
alleles of a single gene
control coat color
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Night-flying owls are the
selective pressure that
directionally shifts the allele
frequency
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A typical two-week course of antibiotics can
exert selection pressure on over a thousand
generations of bacteria
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Antibiotic resistant strains are now found in
hospitals and schools
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Stabilizing selection
 Natural selection that
favors an intermediate
phenotype and
eliminates extreme forms
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Disruptive selection
 Natural selection that favors
extreme forms of a trait and
eliminates the intermediate
forms