Download Darwin`s Journey

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Darwin’s Journey to the Theory of Natural Selection:
Galapagos Islands:
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One unique place Darwin visited on his HMS Beagle trip was the Galapagos Islands. These islands are found 600
miles west of Ecuador in South America. Darwin noticed that the animals and plants on the Galapagos Islands were a lot
like those in Ecuador. However, they were not exactly the same. The finches of the Galapagos Islands, for example,
were a little different from the finches in Ecuador. Additionally, the finches on each island differed from the finches on
the other islands. Darwin observed that each different group of finches had different size and shape beaks and each
group had their own unique feeding habits.
After returning to England, Darwin puzzled over the animals of the Galapagos Islands. He tried to explain why
the animals seemed so similar to each other yet had so many different adaptations. For example, Darwin learned that
the 13 different finches he had studied were each a separate species. Each species was adapted to their own island
habitat. Darwin hypothesized that the island finches were descended from South American finches. The first finches on
the islands may have been blown from South America by a storm. A few individual finches then migrated to neighboring
islands where they became isolated and exposed to a new environment. Over many generations, the finches may have
adapted to different ways of life on the different islands which included the types of food each species of finch relied on
for survival. Eventually they became a separate species from the finches on neighboring islands.
Describe what Darwin learned from studying the finches.
Charles Lyell:
During Darwin’s journey on the H.M.S. Beagle he had an opportunity to read the first volume of his good friend,
Charles Lyell’s newly published book The Principles of Geology. Lyell proposed in his book that the earth was very old,
that it had been slowly changing for millions of years, and that it was still changing. These changes were taking place
from weathering, erosion and deposition. Most of the geologists of the time did not think the Earth was old enough to
allow for slow changes.
After Darwin returned home from his voyage, he spent a great deal of time studying his notes, reading, and
conversing with colleagues. He incorporated the ideas from Lyell’s book about the earth into his own thoughts on how
life changes on earth. Using Lyell’s hypothesis, Darwin concluded that gradual geologic changes over long periods of
time could cause life to change over that same long period of time.
Describe what idea Darwin used from Lyell’s publication.
Selective Breeding:
Darwin also studied the selective breeding of domestic animals and crops. By selecting parents with the most
desirable traits, farmers and animal breeders can raise more desirable offspring. Breeders, for instance, select cattle for
increased milk production (Holstein), for high-butterfat milk (Jersey), or for meat (Hereford). Animal breeders and
farmers determine which members of the population shall reproduce and which shall not. Any domesticated plant or
animal bred to produce desirable characteristics is the result of artificial selection. The striking changes produced over
relatively few generations are powerful proof that species can evolve. Darwin suspected that a selection process also
occurred in nature. If we can select for useful traits in organisms through selective breeding; why can’t nature select
traits in organisms that make them more successful to survive.
How does selective breeding relate to Darwin’s idea?
Thomas Malthus:
Shortly after Darwin returned to England, he read An Essay on the Principles of Population by the economist
Thomas Malthus. Malthus stated in his essay that the human population was growing so fast that the supply of
resources could not keep up with demand. Malthus reasoned that the human population tends to increase
exponentially. For example, if each pair of parents produced four children, the new generation would have 4 individuals
to replace the 2 that had produced them. The next generation would have 8, the next 16, and so on. This type of
population growth will eventually exceed its available resources. According to Malthus, when a population exceeds its
resources, disasters such as war, starvation, or widespread disease limit the population’s growth.
Darwin recognized that Malthus’ principles applied not only to humans, but to all species. Any species
can produce many offspring. He also knew that the populations of all species are limited by starvation, disease,
competition, and predation. Only a limited number of individuals survive to reproduce. Darwin reasoned that the
offspring of the survivors inherit traits that help the offspring survive in their environment.
How did Darwin apply Malthus’ principles to his own theory?
Alfred Wallace:
In 1858, Alfred Wallace, a young British naturalist and explorer, wrote Darwin from Malaysia while he was on an
expedition. Wallace was seeking Darwin’s advice about a theory he had. At the time Darwin was one of the leading
naturalists of England. However, Wallace had no idea of Darwin’s life work on his theory of natural selection because
Darwin had only shared his ideas with a few close colleagues. Wallace sent Darwin an essay on his theory and it turned
out that Wallace had struck upon the theory of natural selection that Darwin had been researching for 20 years.
Wallace’s short sketch was far from the massive body of evidence Darwin had collected, but its core ideas were similar.
Darwin and Wallace agreed that Wallace’s essay should be published along with a summary of Darwin’s theory.
A year later, in 1859, Darwin published his book under the title The Origin of Species. Darwin’s book was fully supported
by examples and 20 years of research and influence. His theory on how evolution works was eventually accepted
around 1865 by most of the leading scientists of his time. Without Wallace’s prompting, Darwin might never have
published his theory during his lifetime.
How did Wallace influence Darwin?