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 _________________________.