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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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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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
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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.
3.
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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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 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
 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?

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:

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
 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?



 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
Liquid containing amino acids and other organic compounds
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Spark simulating lightning storms
Condensation chamber
Cold water cools chamber, causing droplets to form.


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.
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
Formation of Microspheres

Microspheres are not cells, but they have selectively permeable membranes and can store and release energy.
Evolution of RNA and DNA
•
• 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

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.


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
Aerobic bacteria
Ancient Prokaryotes
Nuclear envelope evolving
Photosynthetic bacteria
Mitochondrion
Ancient Anaerobic
Prokaryote
Chloroplast
Plants and plantlike protists
Primitive Aerobic
Eukaryote
Primitive Photosynthetic
Eukaryote
Animals, fungi, and non-plantlike protists
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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
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Primitive Aerobic Eukaryote

Prokaryotes that carried out photosynthesis evolved into chloroplasts.
Photosynthetic bacteria
Chloroplast
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Primitive Photosynthetic Eukaryote


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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