Name: ____________________________________ Date: _______________________ !
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Chapter 15 Notes – Darwin’s Theory of Evolution Section 15-3 Darwin Presents His Case (p. 378-381) After examining all of the _____________________ he collected from the
Galapagos Islands, Darwin realized that each island species looked a lot like similar species on the South American __________________________. Yet the
island species were clearly ____________________ from the mainland species and from one another.
Publication of On the Origin of Species
Darwin filled notebooks with his ideas about species diversity and the _______________________ process.
• These ideas challenged fundamental scientific ________________ of his
day. • Eventually, Darwin published his book, On the Origin of Species.
In his book, Darwin:
• proposed a mechanism for evolution called __________________
____________________. • presented evidence that evolution has been taking place for
__________________ of years—and continues in all living things.
Many considered his work brilliant, while others strongly _________________ his arguments.
Natural Variation and Artificial Selection
Darwin argued that instead of species being perfect and unchanging, there is __________________ ______________________ found in all types of organisms.
• Natural variation = differences among individuals of a
_________________
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• Variation is present in species in _________________, farm crops, and
livestock
Some cows gave more ______________ than others. Some plants produced larger _______________ than others.
• Darwin proposed that much of this variation could be
_____________________, or passed on to the next generation.
By studying farmers and breeders, Darwin noted that they routinely used ____________________ to improve their crops and livestock.
• He noted that plant and animal breeders would breed only the ___________________ hogs, the _____________________ horses, or the
cows that produced the most milk. o Darwin terms this process _____________________ selection.
This produced a wide range of plants and animals that
looked very different from their ________________________. How is natural variation used in artificial selection? In artificial selection, ________________ provided the variation among different organisms, and ________________ selected those variations that they found useful.
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Evolution by Natural Selection Darwin compared processes in nature to artificial selection. By doing so, he developed a scientific ______________________ to explain how evolution occurs.
The Struggle for Existence Darwin realized that high ______________ rates and a shortage of life’s basic
______________ would force organisms to compete for ________________________.
• The struggle of existence means that members of each species ______________________ regularly to obtain food, living space, and other
necessities of life. • In this struggle, _______________________ that are faster or have an
effective method of hunting catch more prey. Those _____________ that
are faster, better camouflaged, or better protected avoid being caught. o The struggle for existence was central to Darwin’s theory of
____________________.
How is natural selection related to a species’ fitness? Survival of the Fittest
The ability of an individual to survive and reproduce in its specific environment is __________________.
• Darwin proposed that fitness is the result of __________________________. o An adaptation is any inherited characteristic that increases an
organism’s chance of _____________________.
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• Successful adaptations enable organisms to become better suited to their
environment and better able to ___________________ and ______________________.
o Adaptations can be __________________ characteristics, such as a
porcupine’s sharp quills, or more __________________ features, such as behavior in which some animals live and hunt in groups.
The concept of fitness was central to the process of evolution by natural selection.
• Generation after generation, individuals compete to survive and produce ____________________. Because each individual differs from other
members of its species, each has _________________ advantages and
disadvantages. • Individuals with characteristics that are not well suited to their
environment (__________ levels of fitness) either __________ or leave __________ offspring.
• Individuals that are better suited to their environment (___________ levels of fitness) survive and reproduce most __________________________.
o Darwin called this process survival of the ________________. Because of its similarities to artificial selection, Darwin referred to the survival of
the fittest as ____________________ _______________________. • In natural selection, the traits being ___________________ for—therefore
increasing over time—contribute to an organism’s __________________ in
its environment. o Natural selection cannot be seen directly; it is observed as
changes in a _______________________ over many successive generations.
Over time, natural selection results in _____________________ in the inherited characteristics of a population. These changes increase a species’ fitness in its _________________________.