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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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Darwin's Observations
 He observed many plants and animals were
well suited to the environments they
inhabited.
 He was impressed by which organisms
survived and produced offspring.
 Darwin was confused by species lived and did
not live.
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Before Darwin, there were scientists
who shaped the way that scientists
viewed a round world.
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Hutton and Lyell's Principles of Geology
1. Scientists must explain past events in
terms of observed processes.
2. Processes that shaped the Earth
millions of years ago still continue.
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Understanding geology influenced
Darwin:
If the Earth could change over time,
life might change too.
It would have taken years for life to
change like Lyell suggested.
This is only possible if the Earth is
extremely old.
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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 proposed:
1. selective use or disuse of organs: organisms
gained or lost certain traits during their
lifetime.
2. Traits could then be passed on to their
offspring.
3. Over time, this process led to change in a
species.
Flaws: Tendency toward perfection
Use and Disuse
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Lamarck's Hypothesis
A male fiddler
crab uses its front
claw to ward off
predators and to
attract mates.
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Lamarck's Hypothesis
Because the front
claw is used
repeatedly, it
becomes larger.
This characteristic
(large claw) is
passed onto its
offspring.
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Evaluating Lamarck's Hypotheses
Lamarck did not know:
 how traits are inherited.
 that an organism’s behavior has no
effect on its heritable characteristics.
 His idea of evolution was wrong.
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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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Hutton and Lyell recognized that geological processes
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of the past differ from those of the present.
indicate that Earth is many millions of years old.
operate quickly, often over thousands of years.
always involve violent events like volcanoes, earthquakes, and
floods.
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Which of the following scientists proposed the
hypothesis of selective use and disuse?
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Charles Darwin
Jean-Baptiste Lamarck
Thomas Malthus
Charles Lyell
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The scientist that proposed that Earth is shaped by
geological forces that took place over long periods of time
is:
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Malthus
Hutton
Darwin
Lamarck
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Natural selection affects which individuals survive and
reproduce and which do not.
Evolution: any change over time in the relative
frequencies of alleles in a population.
Populations, not individual organisms, can evolve over
time.
Natural selection on single-gene traits can lead
to changes in allele frequencies and thus to
evolution.
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Natural selection can affect the
distributions of phenotypes in any of
three ways:
 directional selection
 stabilizing selection
 disruptive selection
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Directional Selection: when individuals
at one end of the curve have higher
fitness than individuals in the middle or
at the other end.
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Stabilizing Selection: when individuals near the
center of the curve have higher fitness than
individuals at either end of the curve.
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Disruptive Selection: when individuals at the
upper and lower ends of the curve have
higher fitness than individuals near the
middle.
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Genetic drift (random change in allele frequency)
occurs when a small group of individuals colonizes
a new habitat.
Individuals may carry alleles in different relative
frequencies than did the larger population from
which they came.
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Evolution Versus Genetic Equilibrium
 The Hardy-Weinberg principle states
that allele frequencies remain
constant unless one or more factors
cause the frequencies to change.
 Genetic equilibrium: When allele
frequencies remain constant.
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Five conditions are required to maintain
genetic equilibrium from generation to
generation:
 there must be random mating,
 the population must be very large,
 there can be no movement into or out of
the population,
 there can be no mutations, and
 there can be no natural selection.
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The situation in which allele frequencies remain
constant in a population is known as
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genetic drift.
the founder effect.
genetic equilibrium.
natural selection.
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Which of the following conditions is required to
maintain genetic equilibrium in a population?
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movement in or out of the population
random mating
natural selection
small population
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 Scientists
infer that about four billion years
ago, Earth cooled and solid rocks formed on
its surface.
 Millions of years later, volcanic activity shook
Earth’s crust.
 About 3.8 billion years ago, Earth’s surface
cooled enough for water to remain a liquid,
and oceans covered much of the surface.
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The
First Organic Molecules
 Could organic molecules have evolved
under conditions on early Earth?
 In the 1950s, Stanley Miller and Harold
Urey tried to answer that question by
simulating conditions on the early Earth
in a laboratory setting.
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Miller and Urey’s Experiment
Mixture of gases
simulating
atmosphere of
early Earth
Water
vapor
Spark simulating
lightning storms
Condensation
chamber
Cold water cools
chamber, causing
droplets to form.
Liquid containing amino
acids and other organic
compounds
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 Miller
and Urey's experiments suggested
mixtures of the organic compounds
necessary for life could have come from
simpler compounds.
 Although their simulations were not
accurate, experiments with current
knowledge yielded similar results.
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The Puzzle of Life's Origin
Evidence suggests that 200–300 million years after
Earth had liquid water, cells similar to modern
bacteria were common.
Formation of Microspheres
 Microspheres are not cells, but they have selectively
permeable membranes and can store and release
energy.
Evolution of RNA and DNA
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Some RNA sequences help DNA replicate under the right
conditions.
Some RNA molecules can grow and duplicate themselves
suggesting RNA might have existed before DNA.
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Evolution of RNA and DNA
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How could DNA and RNA have evolved? Several
hypotheses suggest:
• Some RNA sequences can help DNA replicate under
the right conditions.
• Some RNA molecules can even grow and duplicate
themselves suggesting RNA might have existed
before DNA.
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 The
Endosymbiotic Theory: proposes that
eukaryotic cells arose from living communities
formed by prokaryotic organisms.
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About 2 billion years ago, prokaryotic cells began
evolving internal cell membranes.
The result was the ancestor of all eukaryotic cells.
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Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Aerobic
bacteria
Nuclear
envelope
evolving
Ancient Anaerobic
Prokaryote
Photosynthetic
bacteria
Plants and
plantlike
protists
Mitochondrion
Primitive Aerobic
Eukaryote
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Primitive Photosynthetic
Eukaryote
Animals,
fungi, and
non-plantlike
protists
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Ancient Anaerobic Prokaryote
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
Prokaryotes that
use oxygen to
generate energyrich molecules of
ATP evolved into
mitochondria.
Mitochondrion
Primitive Aerobic Eukaryote
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Prokaryotes that carried out
photosynthesis evolved into
chloroplasts.
Chloroplast
Photosynthetic
bacteria
Primitive Photosynthetic Eukaryote
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Sexual Reproduction and Multicellularity
 Most prokaryotes reproduce asexually. Asexual
reproduction:
 yields daughter cells that are exact copies of the
parent cell.
 restricts genetic variation to mutations in DNA.
 Sexual reproduction shuffles genes in each generation.
In sexual reproduction:
 offspring never resemble parents exactly
 there is an increased probability that favorable
combinations will be produced
 there is an increased chance of evolutionary
change due to natural selection
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