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Chapter 22, 23 and 24
PowerPoint® Lecture Presentations for
Biology
Descent with Modification:
Eighth Edition
Neil Campbell and Jane Reece
A Darwinian View of Life
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• As the 19th century dawned, it was generally
believed that species had remained unchanged
since their creation
• However, a few doubts about the permanence
of species were beginning to arise
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Lamarck’s Hypothesis of Evolution
• Darwin was not the first to propose a theory explaining
the variety of life on earth.
• Jean-Babtiste de Lamarck tried to explain how species
evolve by hypothesizing through use and disuse of
body parts and the inheritance of acquired
characteristics
• For example, in giraffes, Lamarck’s theory said that
their long necks came from stretching to reach leaves
on high trees. The more they stretched the longer their
neck grew and then their offspring would have longer
necks…but we know that things that happen to our
bodies during our lifetime are not passed on to our
offspring because it doesn’t affect our DNA. If we lose
a limb, our children will not all be limbless.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Darwin’s Research
• As a boy and into adulthood, Charles Darwin had a consuming
interest in nature
• Darwin first studied medicine (unsuccessfully), and then theology at
Cambridge University
• After graduating, he took an unpaid position as naturalist and
companion to Captain Robert FitzRoy for a 5-year around the world
voyage on the Beagle
• During his travels on the Beagle, Darwin collected specimens of
South American plants and animals
• He observed adaptations of plants and animals that inhabited many
diverse environments
• Darwin was influenced by Lyell’s Principles of Geology and thought
that the earth was more than 6000 years old
• His interest in geographic distribution of species was kindled by a
stop at the Galápagos Islands near the equator west of South
America
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
GREAT
BRITAIN
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
The
Galápagos
Islands
AFRICA
Pinta
Genovesa
Equator
Marchena
Santiago
Fernandina
Isabela
Daphne
Islands
Pinzón
Santa
Santa
Cruz
Fe
Florenza
SOUTH
AMERICA
AUSTRALIA
PACIFIC
OCEAN
San
Cristobal
Cape of
Good Hope
Tasmania
Española
Cape Horn
Tierra del Fuego
New
Zealand
Darwin’s Focus on Adaptation
• Darwin had trouble explaining the observations he
made about the finches and turtles of the Galapagos
simply as “growing” longer beaks or necks.
• In reassessing his observations, Darwin perceived
adaptation to the environment and the origin of new
species as closely related processes also now known
as natural selection. Nature would “choose” which
organisms survive on the basis of their fitness.
• From studies made years after Darwin’s voyage,
biologists have concluded that this is indeed what
happened to the Galápagos finches
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
(a) Cactus-eater
(c) Seed-eater
(b) Insect-eater
• In 1844, Darwin wrote an essay on the origin of
species and natural selection but did not
introduce his theory publicly, anticipating an
uproar
• In June 1858, Darwin received a manuscript
from Alfred Russell Wallace, who had
developed a theory of natural selection similar
to Darwin’s
• Darwin quickly finished The Origin of Species
and published it the next year
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Origin of Species
• Darwin came to his ideas by a number of observations
–
Each species produces more offspring than can survive.
–
These offspring compete with one another for the limited resources
available to them.
–
Organisms in every population vary.
–
The offspring with the most favorable traits or variations are the most
likely to survive and therefore produce more offspring.
• Darwin developed two main ideas:
–
Natural selection is a cause of adaptive evolution. Individuals whose
inherited traits give them a higher probability of surviving and
reproducing in a given environment tend to leave more offspring than
other individuals.
–
Descent with modification explains life’s unity and diversity. This unequal
ability of individuals to survive and reproduce will lead to the
accumulation of favorable traits in the population over generations
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Natural Selection
• Individuals with certain heritable characteristics survive
and reproduce at a higher rate than other individuals
• Natural selection increases the adaptation of organisms to
their environment over time
• If an environment changes over time, natural selection may
result in adaptation to these new conditions and may give
rise to new species
• Note that individuals do not evolve; populations evolve
over time
• Natural selection does not create new traits, but edits or
selects for traits already present in the population
• The local environment determines which traits will be
selected for or selected against in any specific population
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
(a) A flower mantid
in Malaysia
(b) A stick mantid
in Africa
Direct Observations of Evolutionary Change
• Two examples provide evidence for natural
selection: the effect of differential predation on
hummingbird populations and the evolution of
drug-resistant HIV
Natural Selection of
Hummingbirds (Video 4)
Put in Video Clip from
Darwin’s Dangerous Idea
(44:23)
•An example of how advanced organs in our
bodies evolve from more rudimentary organs.
Put in Video Clip from
Darwin’s Dangerous Idea
(1:03:00)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Types of Selection
• Directional Selection
• Stabilizing Selection
• Disruptive Selection
• Sexual Selection
• Artificial Selection
Directional Selection
Stabilizing Selection
Disruptive Selection
Sexual Selection
• Sexual selection is natural selection for mating success
• It can result in sexual dimorphism, marked differences between
the sexes in secondary sexual characteristics
• Intrasexual selection is competition among individuals of one sex
(often males) for mates of the opposite sex
• Intersexual selection, often called mate choice, occurs when
individuals of one sex (usually females) are choosy in selecting
their mates
• Male showiness due to mate choice can increase a male’s chances
of attracting a female, while decreasing his chances of survival
• How do female preferences evolve?
• The good genes hypothesis suggests that if a trait is related to male
health, both the male trait and female preference for that trait
should be selected for
Fig. 23-16
EXPERIMENT
Female gray
tree frog
SC male gray
tree frog
LC male gray
tree frog
SC sperm  Eggs  LC sperm
Offspring of Offspring of
SC father
LC father
Fitness of these half-sibling offspring compared
RESULTS
Fitness Measure
1995
1996
Larval growth
NSD
LC better
Larval survival
LC better
NSD
Time to metamorphosis
LC better
(shorter)
LC better
(shorter)
NSD = no significant difference; LC better = offspring of LC males
superior to offspring of SC males.
Artificial Selection
• Darwin noted that humans have modified other
species by selecting and breeding individuals
with desired traits, a process called artificial
selection
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Terminal
bud
Cabbage
Brussels sprouts
Flower
clusters
Broccoli
Lateral
buds
Descent with Modification
• Darwin never used the word evolution in the
first edition of The Origin of Species
• The phrase descent with modification
summarized Darwin’s perception of the unity of
life
• The phrase refers to the view that all
organisms are related through descent from an
ancestor that lived in the remote past
• In the Darwinian view, the history of life is like a
tree with branches representing life’s diversity
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Moeritherium
Barytherium
Deinotherium
Mammut
Platybelodon
Stegodon
Mammuthus
Elephas maximus
(Asia)
Loxodonta
africana
(Africa)
Loxodonta cyclotis
(Africa)
34
24
Millions of years ago
5.5
2 104 0
Years ago
Decent with
Modification
(Video 3)
Evidence of Evolution in Several Areas
• Paleontology- study of the fossil record
• Biogeography- study of the distribution of flora
(plants) and fauna (animals) in the environment
• Embryology- study of the development of an
organism
• Comparative anatomy- study of the anatomy of
various animals and their homologous and
analogous structures.
• Molecular biology- study of the DNA and
chromosomes of organisms.
The Fossil Record
• By dating fossils and examining geologic strata, scientists have
been able to put together a time scale for the history of life on
earth.
• Fossil evidence indicates that over time organisms of increasing
complexity appeared on the earth. Bacteria and blue-green
bacteria are the first fossils that were preserved from the
Precambrian era. During the beginning of the Paleozoic e ra,
complex multicellular invertebrates dominated life in the oceans.
By the end of the Paleozoic era, plants and animals has
colonized the land surface of the earth.
• The fossil record provides evidence of the extinction of species,
the origin of new groups, and changes within groups over time.
• The Darwinian view of life predicts that evolutionary transitions
should leave signs in the fossil record. Paleontologists have
discovered fossils of many such transitional forms
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
(a) Pakicetus (terrestrial)
(b) Rhodocetus (predominantly aquatic)
Pelvis and
hind limb
(c) Dorudon (fully aquatic)
Pelvis and
hind limb
(d) Balaena
(recent whale ancestor)
Biogeography
• Darwin’s observations of biogeography, the geographic
distribution of species, formed an important part of his theory of
evolution
• Scientists have found related species in widely separated regions
of the world.
• Islands have many endemic species that are often closely related
to species on the nearest mainland or island. For example, Darwin
observed that animals in the Galapagos have traits similar to
those of animals on the mainland of South America.
• Earth’s continents were formerly united in a single large continent
called Pangaea, but have since separated by continental drift
• An understanding of continent movement and modern distribution
of species allows us to predict when and where different groups
evolved.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Embryology
• Comparative embryology reveals anatomical
homologies not visible in adult organisms.
• If you look at the early stages in vertebrate
development, all the embryos look alike. All
vertebrates-including fish, amphibians, birds
and even humans- show fishlike features called
gills slits.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Pharyngeal
pouches
Post-anal
tail
Chick embryo (LM)
Human embryo
Comparative Anatomy
• Scientists have discovered that some animals have similar
structures that serve different functions. For example, a human’s
arm, a cat’s leg, a whale’s fin, and a bat’s wing.
Humerus
• These structures, called homologous structures, are features
Radius
that look similar that represent variations on a structural theme
present in a common ancestor.
Ulna
• In contrast, sometimes animals have features with the same
Carpals
function but that are structurally different, such as a bat’s wing
and an insect’s wing, which are both used to fly but have
Metacarpals
evolved independently of each other. These structures are
called analogous structures.
Phalanges
Whale
Catstructures that
• Finally, thereHuman
are vestigial
are thought to beBat
remnants of features that served important functions in the
organism’s ancestors, such as a human’s tail bone.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 22-19
Branch point
(common ancestor)
Lungfishes
Amphibians
1
Mammals
2
Tetrapod limbs
Amnion
Lizards
and snakes
3
4
Homologous
characteristic
Crocodiles
Ostriches
6
Feathers
Hawks and
other birds
Birds
5
Microbiology
•
Biochemistry reveals similarities between organisms of different
species. For example, the metabolism of vastly different organisms is
based on the same complex biochemical compounds.
•
The protein cytochrome c, essential for aerobic respiration, is one such
universal compound. The universality of cytochrome c is evidence that
all aerobic organisms probably descended from a common ancestor
that used this compound for respiration.
•
Further studies of cytochrome c in different species reveal variations in
the amino acid sequence of this molecule. For example, the
cytochrome c of monkeys and cows is more similar than the
cytochrome c of monkeys and fish. Such similarities and differences
suggest that monkeys and cows ate more closely related than are
monkeys and fish.
•
Scientists can also examine the nucleotide and amino acid sequences
of different organisms’ DNA. From these analyses, we’ve discovered
that organisms that are closely related have a greater proportion of
sequences in common that distantly related species.
Did Humans Evolve? Video 5
Speciation
• Evolution occurs when two organisms undergo
natural selection to the point that the two can no
longer reproduce to create viable offspring. The
endpoint of that particular cycle of evolution is
speciation or the emergence of a new species.
• Allopatric speciation simply means that a
population becomes separated from the rest of the
species by a geographical barrier so that they
can’t interbreed. For example, the squirrels on
each side of the Grand Canyon.
• Sympatric speciation is when two new species
form without any geographic barrier. It is common
in plants.
Reproductive Isolation
• Reproductive isolation is the existence of biological factors
(barriers) that impede two species from producing viable, fertile
offspring
–
Prezygotic barriers block fertilization from occurring by:
• Impeding different species from attempting to mate
– Temporal isolation: Species that breed at different
times of the day, different seasons, or different years
cannot mix their gametes
– Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective barriers
• Preventing the successful completion of mating
– Mechanical isolation: Morphological differences can
prevent successful mating
• Hindering fertilization if mating is successful
– Gametic isolation: Sperm of one species may not be
able to fertilize eggs of another species
– Postzygotic barriers prevent the hybrid zygote
from developing into a viable, fertile adult:
• Reduced hybrid viability: Genes of the different
parent species may interact and impair the
hybrid’s development
• Reduced hybrid fertility: Even if hybrids are
vigorous, they may be sterile
• Hybrid breakdownSome first-generation hybrids
are fertile, but when they mate with another
species or with either parent species, offspring
of the next generation are feeble or sterile
Divergent Evolution
• Divergent evolution is the process of two or more related
species becoming more and more dissimilar.
• The red fox and the kit fox provide an example of two
species that have undergone divergent evolution. The red
fox lives in mixed farmlands and forests, where its red
color helps it blend in with surrounding trees. The kit fox
lives on the plains and in the deserts, where its sandy color
helps conceal it from prey and predators. The ears of the
kit fox are larger than those of the red fox. The kit fox's
large ears are an adaptation to its desert environment. The
enlarged surface area of its ears helps the fox get rid of
excess body heat. Similarities in structure indicate that the
red fox and the kit fox had a common ancestor. As they
adapted to different environments, the appearance of the
two species diverged.
Convergent Evolution
• Convergent evolution is process in which two
unrelated and dissimilar species come to have
similar, or analogous, features often because
they have been exposed to similar selective
pressures.
• For example, sugar glider and flying squirrel;
and the giant armadillo, giant pangolin, giant
anteater, and spiny anteater
• Convergent evolution does not provide
information about ancestry
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Sugar
glider
NORTH
AMERICA
AUSTRALIA
Flying
squirrel
Coevolution
• Coevolution is the joint change of two or more
species in close interaction. Predators and their
prey sometimes coevolve; parasites and their
hosts often coevolve; plant-eating animals and the
plants upon which they feed also coevolve.
• For example, Newt and Garter Snake
Put in The Evolutionary
Arms Race video to
show example (~3:00)
The Smallest Unit of Evolution
• One misconception is that organisms evolve, in
the Darwinian sense, during their lifetimes
• Natural selection acts on individuals, but only
populations evolve
• Genetic variations in populations contribute to
evolution
• Microevolution is a change in allele
frequencies in a population over generations
Population Genetics
•
Mendel’s laws can also extend to the population level.
•
The Hardy-Weinberg law states that even with all the shuffling of
genes that goes on, the relative frequencies of genotypes in a
population will prevail over time. The alleles don’t get lost in the shuffle.
The dominant gene doesn’t become more prevalent, and the recessive
gene doesn’t disappear.
•
The frequency of each allele is described in the equation below. Let “p”
represent the frequency of the dominant allele and “q” represent the
frequency of the recessive allele in the population.
•
The sum of the frequencies must add up to one. p + q = 1 If you know
the value of one of the alleles, then you’ll also know the value of the
other allele.
•
We can also determine the frequency of the genotypes in a poluation
using another equation. p2 + 2pq + q2 = 1 where p2 represents the
homozygous dominants, 2pq represents the heterozygotes and q2
represents the homozygous recessives.
•
For example….
80% CR (p = 0.8)
20% CW (q = 0.2)
Sperm
CR
(80%)
CW
(20%)
64% (p2)
CRCR
16% (pq)
CRCW
16% (qp)
CRCW
4% (q2)
CW CW
64% CRCR, 32% CRCW, and 4% CWCW
Gametes of this generation:
64% CR + 16% CR
= 80% CR = 0.8 = p
4% CW + 16% CW = 20% CW = 0.2 = q
Genotypes in the next generation:
64% CRCR, 32% CRCW, and 4% CWCW plants
Hardy-Weinberg Equilibrium
• The Hardy-Weinberg law says that a population
will be in genetic equilibrium only if it meets these
five conditions
– A large population
– No mutations
– No immigration or emigration (gene flow)
– Random mating
– No natural selection
Violations of the Hardy-Weinberg Law
• Any departure from them results in changes in allele
frequencies in a population.
• The Hardy-Weinberg principle describes a population that
is not evolving
• If a population does not meet the criteria of the HardyWeinberg principle, it can be concluded that the population
is evolving
• Three major factors alter allele frequencies and bring
about most evolutionary change:
– Natural selection (already discussed )
– Genetic drift
– Gene flow
Genetic Drift
• The smaller a sample, the greater the chance
of deviation from a predicted result
• Genetic drift describes how allele frequencies
change from one generation to the next
• Genetic drift tends to reduce genetic variation
through losses of alleles
• Two main examples are known as
– The Founder Effect
– The Bottlenose Effect
The Founder Effect
• The founder effect occurs when a few
individuals become isolated from a larger
population, such as through migration.
• Allele frequencies in the small founder
population can be different from those in the
larger parent population
The Bottleneck Effect
• The bottleneck effect is a sudden reduction in
population size due to a change in the
environment
• The resulting gene pool may no longer be
reflective of the original population’s gene pool
• If the population remains small, it may be
further affected by genetic drift
• Understanding the bottleneck effect can
increase understanding of how human activity
affects other species
Original
population
Bottlenecking
event
Surviving
population
Gene Flow
• Gene flow consists of the movement of alleles
among populations
• Alleles can be transferred through the
movement of fertile individuals or gametes (for
example, pollen)
• Gene flow tends to reduce differences between
populations over time
• Gene flow is more likely than mutation to alter
allele frequencies directly
• Gene flow can decrease the fitness of a
population
• In bent grass, alleles for copper tolerance are
beneficial in populations near copper mines,
but harmful to populations in other soils
• Windblown pollen moves these alleles between
populations
• The movement of unfavorable alleles into a
population results in a decrease in fit between
organism and environment