Download Bio 1B, Spring, 2007, Evolution section 1 of 3 Updated 2/22/07 9:22

Bio 1B, Spring, 2007, Evolution section 1 of 3
Lecture 1
Updated 2/22/07 9:22 AM
 1 Darwin and The Origin of Species
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Reading: 7th edition 438-446; 6th edition 428-437. The Origin of Species is not
required reading, but copies of the first and sixth editions are freely available from
the Gutenberg Project, www.gutenberg.org.
 Logistics
 Office hours: Monday, Tuesday, Wednesday 9-10, 2013 VLSB or by appointment
([email protected])
 Responsible for material in the lectures and lecture notes
• If material is in the text but is not covered in the lectures and notes, it will not be
required for the exams. Updated versions of the notes will reflect what is
presented in lectures. Examples from the labs will be used on the exams when
they illustrate principles from the lectures.
• Sample exam questions will be included with each set of notes. They are
intended to show the types of questions that will be asked on the midterm and
final but not the range of topics that will be covered.
• The 2nd midterm, 6 PM on Friday, April 6, will be on all the material in the
evolution section, including material presented on Wednesday, April 4.
 Any theory of evolution must have three parts.
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The fact of evolution: All living organisms are descended from other living
organisms and ultimately from one or a few ancestors. Darwin called this idea
“descent with modification.”
The pattern of evolution: The pattern is what actually happened. Darwin said that
the pattern is gradual and continuous, not discontinuous.
The mechanism of evolution: Darwin argued that natural selection alone caused
descent with modification.
 Uniformitarian assumption
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Darwin’s theory is based on what is now called the “uniformitarian assumption”
or the assumption of “natural law.”
The uniformitarian assumption is that the rules governing change were the same
in the past as they are today.
The name “uniformitarian” comes from the uniformitarian theory of geology,
which argued that changes in the earth’s surface are the result of processes at
work today. For example, sedimentary rocks were the result of erosion. Darwin
was strongly influenced by the book Principles of Geology by Charles Lyell,
which he read during the voyage of the Beagle. Lyell’s book convincingly
advocated the uniformitarian theory of geology.
The alternative to the uniformitarian assumption is that changes in the past
occurred because of processes that are no longer acting and hence cannot be
observed today, in other words supernatural processes.
Bio 1B, Spring, 2007, Evolution section 2 of 3
Lecture 1
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The uniformitarian assumption does not mean that all change has to be slow and
gradual. A volcanic eruption, a major earthquake, and the impact of a large
meteorite can produce nearly instantaneous changes but they do so in accordance
with laws of physics and chemistry.
The uniformitarian assumption does not mean that rules governing changes in the
past are completely understood or that events are completely predictable.
Weather is governed by the rules of physics and chemistry. Yet, meteorologists
cannot perfectly predict the weather even one day in advance.
The uniformitarian assumption is the basis for all historical science, including
astronomy, geology, and archeology.
The reason for emphasizing the uniformitarian assumption is that it is at the root
of most objections to evolution.
 Outline of the Origin of Species (1859)
 Domesticated species
• The first chapter presents evidence that there is extensive variation within
domesticated plant and animal species. Then it presents evidence that differences
among individuals are inherited and that selection of desired types results in
steady improvements of existing breeds and varieties and in the creation of new
breeds and varieties. This process is called selective breeding or artificial
selection. Darwin used horses, dogs, and pigeons as examples. He said that there
appeared to be no limit to what can be achieved by selective breeding. The facts
presented were generally known and were not controversial.
 Variation in natural species
• The second chapter reviews what was known about variation in natural species. It
emphasizes that there is variation within all natural species and that variation is of
the same type and extent as is seen in domesticated species. Darwin used many
species of British plants as examples. These facts were also known and not
controversial.
 Struggle for existence
• The third chapter introduces Darwin’s essentially new view that natural species
are continually in competition for space, food, water, and other resources. The
struggle for existence is against other members of the same species, against
members of other species and against the physical environment. All animals and
plants have many more offspring than can possibly survive, making the struggle
for existence inevitable. The view of nature that Darwin presented was very
different from the generally accepted view which emphasized the harmony of
nature and the perfection of creation. The ideas in this chapter were influenced by
an essay written Thomas Malthus.
 Natural selection
• The fourth chapter describes Darwin’s mechanism of evolution — natural
selection — as a necessary consequence of what he presented in the second and
third chapters. Differences among individuals in their abilities to succeed in the
struggle for existence result in some individuals having more offspring than
others. Those offspring that inherit the traits that made their parents successful in
the struggle for existence will themselves be better adapted. As a result, the
Bio 1B, Spring, 2007, Evolution section 3 of 3
Lecture 1
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Updated 2/22/07 9:22 AM
composition of the species changes slightly from one generation to the next as the
more successful types became more frequent. Darwin said that, as with selective
breeding, there was no limit to changes that could result from natural selection. It
is the species that evolves, not the individual.
Darwin emphasized that no characteristic could be present only because it
benefits another species. He used nectar in flowers as an example.
 Sample questions (correct answer is underlined)
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Which one of the following was not a part of Darwin’s theory of evolution?
Gradual pattern
discontinuous pattern
Uniformitarian assumption
Inheritance
Descent with modification
Which one of the following best describes the uniformitarian assumption?
Changes in the past were more rapid than occur today.
Changes in the past were governed by the same rules as are changes today.
Changes in the past were slow and gradual.
Changes in the past were governed by rules that are different from those
governing changes today.
Changes in the past were caused by natural selection.
What was the role of an essay on human populations by Thomas Malthus in the
development of Darwin’s theory?
Darwin became convinced of the importance of variation.
Darwin became convinced of the importance of inheritance.
Darwin became convinced of the importance of the struggle for existence.
Darwin became convinced of the importance of descent with modification.
Darwin became convinced of the importance of the uniformitarian theory of
geology.
What did Darwin say about variation in natural species?
Variation between species results in gradual evolution.
Variation between species results in rapid evolution.
Variation is found within all natural species.
Variation within species is explained by the uniformitarian assumption.
Variation within domesticated species is different from variation within natural
species.