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Chapter 17 Lecture
Conceptual
Integrated Science
Second Edition
The Evolution
of Life
© 2013 Pearson Education, Inc.
This lecture will help you understand:
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The Origin of Life
Did Life on Earth Originate on Mars?
Early Life on Earth
Charles Darwin and The Origin of Species
How Natural Selection Works
Adaptation
Staying Warm and Keeping Cool
Evolution and Genetics
How Species Form
Evidence of Evolution
Fossils: Earth's Tangible Evidence of Evolution
The Evolution of Humans
History of Science: The Peppered Moth
Science and Society: Antibiotic-Resistant Bacteria
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The Origin of Life
• For thousands of years, people believed that life
was created through spontaneous generation,
the sudden emergence of living organisms from
nonliving materials.
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The Origin of Life
• In 1862, Louis Pasteur demonstrated that life did
not arise from nonlife.
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• He designed a flask that kept out dust and other
airborne particles
• He filled the flask with meat broth, and let it sit
• No life emerged
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The Origin of Life
• Life originated billions of years ago on a young
Earth very different from the Earth of today.
• The Miller and Urey experiment modeled the
young Earth's atmosphere and
oceans.
• When Miller and Urey shot
electric sparks through the model
to simulate lightning, complex
organic molecules formed.
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• Many complex organic molecules could have
been formed
– Including Amino Acids, Proteins, Sugars and
Lipids
• But many scientist question the validity of this
experiment
– Because the Earth’s atmosphere may have
been different
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The Origin of Life
• There are two alternative hypotheses for the
origin of organic molecules on Earth:
– Organic molecules came to Earth on incoming
meteorites.
– Organic molecules were synthesized in deepsea environments.
• But, how do you get from organic molecules to
cells?
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The Origin of Life
• Liposomes form spontaneously when certain
lipids are added to water. Liposomes
– have double membranes similar to cell
membranes.
– can grow, shrink, and divide.
– run chemical reactions
inside their membranes.
– control what molecules
move into and out of them.
– they are not alive.
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The Origin of Life
• Living cells also need genes.
• Scientists now believe that the first genes were
made of RNA, not DNA.
– Short strands of RNA can spontaneously
assemble from individual RNA nucleotides.
– RNA can replicate by itself.
• Liposomes may have captured RNA "genes,"
forming the first primitive cells on Earth.
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Did Life on Earth Originate on Mars?
• In 1996, scientists found what resembled tiny,
fossilized bacteria in a Martian meteorite.
• Mars may have once been a much warmer and
wetter planet.
• The supposed fossils may be too small to be
fossilized bacteria.
• NASA continues to explore the possibility of life
on Mars.
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Early Life on Earth
• The origin of autotrophs
– Earth's earliest living organisms
• were marine prokaryotes (3.5 billion years old).
• lived with no free oxygen.
• were heterotrophs that obtained energy and food from
outside sources.
– The evolution of autotrophs, organisms able to
convert inorganic molecules into food and organic
molecules, was a key event in the history of life.
• Photosynthesizers use energy from the Sun.
• Chemoautotrophs use energy from certain inorganic
chemicals.
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Early Life on Earth
• The oxygenation of the atmosphere
– Cyanobacteria are photosynthetic bacteria
that produce oxygen as a by-product of
photosynthesis.
– They arose 2.7 billion years ago.
– They changed the environment.
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Early Life on Earth
• The first eukaryotes
– Eukaryotes appeared about 2 billion years ago.
– The nucleus and most organelles most likely
originated from inward foldings of the cell membrane.
– According to the endosymbiotic theory, mitochondria
and chloroplasts (have their own DNA) evolved from
prokaryotes living inside the earliest eukaryotic cells.
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Charles Darwin and The Origin of Species
• For thousands of years, people believed that
species on Earth did not change.
• But then what are fossils?
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Charles Darwin and The Origin of Species
• Jean Baptiste Lamarck argued that modern species
were descended from ancestors that had evolved to
become better adapted to their environments.
• Lamarck believed
that organisms
acquired new traits
over their lifetimes
and then passed
these traits to their
offspring. He called
this the inheritance
of acquired characteristics.
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Charles Darwin and The Origin of Species
• Charles Darwin argued that evolution—inherited
changes in populations of organisms over
time—had produced all the living forms on Earth.
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Lamarck's Evolution Hypotheses
Lamarck's Evolution Hypotheses
Jean-Baptiste Lamarck recognized that:
– living things have changed over time.
– all species were descended from other species.
– organisms were adapted to their environments.
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Lamarck's Evolution Hypotheses
Lamarck proposed that by selective use or
disuse of organs, organisms acquired or lost
certain traits during their lifetime. These traits
could then be passed on to their offspring.
Over time, this process led to change in a
species.
Flaws: Tendency toward perfection
Use and Disuse
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Lamarck's Evolution Hypotheses
A male fiddler
crab uses its front
claw to ward off
predators and to
attract mates.
Lamarck's Hypothesis
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Lamarck's Evolution Hypotheses
Because the front
claw is used
repeatedly, it
becomes larger.
Lamarck's Hypothesis
This characteristic
(large claw) is
passed onto its
offspring.
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Lamarck's Evolution Hypotheses
Evaluating Lamarck's Hypotheses
Lamarck’s hypotheses of evolution are incorrect in
several ways.
Lamarck did not know:
– how traits are inherited.
– that an organism’s behavior has no effect on its heritable
characteristics.
However, he paved the way for the work of later
biologists.
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Voyage of the Beagle
Voyage of the Beagle
In 1831, Darwin set sail from England aboard the
H.M.S. Beagle for a voyage around the world.
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Voyage of the Beagle
During his travels, Darwin made numerous
observations and collected evidence that led
him to propose a hypothesis about the way life
changes over time.
That hypothesis has become the theory of
evolution (aka theory of natural selection).
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Darwin's Observations
Darwin's Observations
• He observed many plants and animals were well
suited to the environments they inhabited.
• He was impressed by the ways in which organisms
survived and produced offspring.
• Darwin was puzzled by where different species lived
and did not live.
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Darwin's Observations
• Living Organisms and Fossils
• Darwin collected the preserved remains of ancient
organisms, called fossils.
• Some of those fossils resembled organisms that
were still alive.
• Others looked completely unlike any creature he had
ever seen.
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Charles Darwin and The Origin of Species
• Darwin was inspired by the observations he made as the
naturalist aboard the H.M.S. Beagle as it sailed around
South America from 1831 to 1836.
• For example, the 13 species of finches on the
Galápagos Islands varied in beak size and shape,
depending on their diet. How had the beaks of the
finches come to vary in this way?
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Charles Darwin and The Origin of Species
• Darwin was also inspired by
– the work of geologist Charles Lyell, who
argued that Earth's geologic features were
built by gradual processes over millennia.
– the work of economist Thomas Malthus, who
wrote about famine and the struggle of
humans over resources.
– Malthus reasoned that if the human
population continued to grow unchecked,
sooner or later there would be insufficient
living space and food for everyone.
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An Ancient, Changing Earth
• Lyell's Principles of Geology
• Lyell stressed that scientists must explain past
events in terms of processes that they can actually
observe.
• The processes that shaped the Earth millions of
years earlier continue in the present.
An Ancient, Changing Earth
This understanding of geology influenced
Darwin:
• If the Earth could change over time, life might change
as well.
• It would have taken many years for life to change in
the way Lyell suggested.
This would have been possible only if the Earth
were extremely old.
How Natural Selection Works
• In any population of organisms, individuals have
many traits that show variation.
• Traits that are determined at least partly by
genes are heritable, passed from parents to
offspring.
• Organisms that possess variable heritable traits
that are advantageous leave more offspring than
organisms without the advantageous traits. This
is natural selection.
• Advantageous traits become more common in a
population, resulting in adaptation.
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How Natural Selection Works
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Adaptation
• Adaptations are traits that make organisms well
suited to living and reproducing in their
environments.
• Adaptations can relate to various aspects of an
organism's life:
– Survival adaptations (acquire resources)
– Sexual selection, which leads to the evolution
of adaptations that help organisms acquire
mates
– Bearing and raising young
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Staying Warm and Keeping Cool
• Mammals thermoregulate, maintaining
a fairly constant body temperature.
• The surface-area-to-volume ratio is an
important factor in thermoregulation.
It affects the size and shape of animals.
– Size: Animals found in cold habitats
are often larger than related species
living in warm habitats.
– Shape: Animals found in cold
habitats tend to have short legs and
small ears. Animals found in warm
habitats have long legs and large
ears.
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Evolution and Genetics
• The incorporation of modern genetics into
Darwin's theory of evolution took place in the
middle of the 20th century.
• This led to a focus on evolution as changes in
the allele frequencies of genes over time.
• Allele frequencies describe how common
different alleles for a gene are in the population.
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History of Science: The Peppered Moth
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History of Science: The Peppered Moth
• Peppered moths in England had always been light with a
scattering of peppery flakes. This made them well
camouflaged from birds (their main predators) in a
habitat of lichen-covered trees.
• During the Industrial Revolution, pollution caused trees
to become darkened with soot.
• More and more dark moths were seen in the peppered
moth population.
• After antipollution laws were passed, the soot
disappeared.
• Light moths increased in number. The dark moths have
all but disappeared.
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History of Science: The Peppered Moth
• Kettlewell's experiments confirmed that natural selection
was responsible for changes in coloration in peppered
moth populations.
• Kettlewell released and recaptured marked moths. He
recaptured more dark moths in polluted habitats and
more light moths in unpolluted habitats.
• Kettlewell also placed moths on trees and filmed birds
eating the moths. Birds ate more light moths in polluted
habitats and more dark moths in unpolluted habitats.
• Challenges to Kettlewell's work resulted in his
experiments being repeated by Michael Majerus.
Kettlewell's results were confirmed.
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Science and Society: Antibiotic-Resistant
Bacteria
• Antibiotic resistance has become a serious health issue.
• Antibiotic resistance is the result of natural selection.
• When a patient takes a course of antibiotics, a few
naturally resistant bacteria may survive the treatment.
These reproduce. Eventually, strains of bacteria exist
that cannot be controlled by the antibiotic.
• All antibiotic use contributes to antibiotic resistance.
• We must learn to take antibiotics only for bacterial
infections, and then to complete the course of treatment.
• Antibiotics should not be used to promote the growth of
livestock.
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Science and Society: Antibiotic-Resistant
Bacteria
• Ways to slow the development of antibiotic
resistance in bacteria:
– Take antibiotics only when needed.
– Take the entire course of antibiotics.
– Use antibiotics responsibly in agriculture.
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• Notice that, although natural selection affects
genes and allele frequencies, it does not act
directly on genes.
– Natural Selection acts on the organisms
phenotype (traits), not on its genotype
(genes).
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Evolution and Genetics
• Mechanisms of Evolution
– Natural selection
• A specific allele may be advantageous and allow
organisms with the allele to reproduce more than
organisms with a different allele.
• More copies of the advantageous allele are passed
to the next generation, and the frequency of the
advantageous allele increases in the population.
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Evolution and Genetics
• Mechanisms of Evolution (continued)
– Mutation pressure
• A genetic mutation may be more likely to turn one
allele into a second allele than vice versa.
• Like the previous moth example
– Genetic drift
• Genetic drift is the evolution of populations due to
chance.
• Genetic drift is particularly important in small
populations.
• Ex – a worm wipes out ½ the moth population
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– By chance the light ones survive
– This is not natural selection it is evolution by chance
• Flipping the coin 10 times vs 100 times gives a
different result.
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Evolution and Genetics
• Mechanisms of Evolution (continued)
– Gene flow
• Changes in allele frequency result from the
movement of alleles into or out of a population,
such as through migration.
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Variation
• Natural selection cannot happen without
variation.
• Populations with more variation have a better
chance of adapting to a changing environment.
– Ex – The moths
• What if there were only light moths and not dark
moths
• Would they have survived if the habitat shifted to
favor dark coloration?
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How Species Form
• A species is a group of organisms whose
members can breed with one another but not
with members of other species.
• Speciation is the formation of new species.
• The key to speciation is the evolution of
reproductive barriers that prevent two groups of
organisms from interbreeding.
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How Species Form
• There are two kinds of reproductive barriers:
– Prezygotic reproductive barriers (before
fertilization) prevent individuals of different
species from mating or prevent fertilization
from occurring if they do mate.
• When, where they breed, sex organs may not fit
appropriately and courtship rituals
– Postzygotic reproductive barriers (after
fertilization) occur when mating results in
hybrids that do not survive or are sterile,
unable to reproduce.
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How Species Form
CHECK YOUR NEIGHBOR
• Is a mule a demonstration of a prezygotic
reproductive barrier or a postzygotic
reproductive barrier?
• Explain your answer to your neighbor.
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How Species Form
• Two ways speciation can occur:
– In allopatric speciation, speciation occurs after
a geographic barrier divides a population into
two isolated populations.
• Mountain range, river, ocean, canyon
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• Adaptive Radiation – type of allopatric speciation
– Where many new species, each adapted to a
distinct way of life, evolved from a single
ancestor.
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How Species Form
• Two ways speciation can occur (continued):
– In sympatric speciation, speciation occurs
without a geographic barrier.
• Examples: hybridization and chromosomal
changes such as polyploidy (in plants, it is deadly
in animals).
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Evidence of Evolution
• Observations of natural selection in action
– Resistance to myxoma virus in Australian
rabbits
– Peppered moth coloration and camouflage
– Antibiotic-resistant bacteria
– Evolution of the beaks of Darwin's finches
after a drought
– Many other documented examples
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Evidence of Evolution
• Artificial selection
– In domesticated animals and crops, such as
dogs, racehorses, and corn
• Similarities in body structures
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Evidence of Evolution
• Vestigial organs
• DNA and molecular evidence
– Similar DNA sequences in related species
• Patterns of development
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Evidence of Evolution
• Hierarchical organization of living things
– Nested groups, or "groups within groups"
• Biogeography
– The study of how species are distributed on
Earth
– Organisms evolved in a certain place and
then left descendants in the places where
they were able to spread.
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Fossils: Earth's Tangible Evidence of
Evolution
• Fossils allow us to follow the evolution of certain
groups of organisms over time.
• The evolution of the whale blowhole
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Fossils: Earth's Tangible Evidence of
Evolution
• The evolution and loss of whale hind legs
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Fossils: Earth's Tangible Evidence of
Evolution
• Archaeopteryx, an early bird evolved from
dinosaur ancestors
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The Evolution of Humans
• Humans are
– primates—we share an ancestry with
monkeys and apes.
– hominids—the primate group that includes
Homo sapiens and extinct relatives.
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The Evolution of Humans
• The fossil record has allowed us to document
some aspects of human evolution.
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