Darwin

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Darwins Theory

• by Federico Brovelli

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Charles Robert Darwin
Charles Robert Darwin (12 February 1809 19
April 1882) was an English naturalist. He
established that all species of life have
descended over time from common ancestors, and
proposed the scientific theory that explains that
this branching pattern of evolution, resulted
from a process that he called natural selection.
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Darwin published his theory with some evidence
for evolution in his book On the Origin of
Species, overcoming scientific rejection of
earlier concepts of transmutation of species. By
the 1870s the scientific community and much of
the general public had accepted evolution as a
fact.
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However, many favoured competing explanations and
it was not until the emergence of the modern
evolutionary synthesis from the 1930s to the
1950s that a broad consensus developed in which
natural selection was the basic mechanism of
evolution. 
In modified form, Darwin's scientific discovery
is the unifying theory of the life sciences,
explaining the diversity of life.
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The journey on the Beagle
The Beagle was a ship used for a cartographic
consignment of five years, around the coasts of
South America. When Darwin was young, he was
recommended to Robert Fitzrov, the captain of
this ship.
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The possibility of working, during the journey
directly on the field, allowed him to study the
geological characteristics of continents,
islands, and a lot of organisms and fossils. He
collected methodically a large amount of samples,
unknown to science this samples, were given to
British Museum, and only those samples were an
enormous scientific contribution.
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Thanks to those studies Darwin began detailed
investigations and in 1838 conceived his theory
of natural selection. Although he discussed his
ideas with several naturalists, he needed time
for extensive research and his geological work
had priority.
He was writing up his theory in 1858 when Alfred
Russel Wallace sent him an essay which described
the same idea, prompting immediate joint
publication of both of their theories.
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Darwins Work
Darwin's work established evolutionary descent
with modification as the dominant scientific
explanation of diversification in nature. 
In 1871 he examined human evolution and sexual
selection in The Descent of Man, and Selection in
Relation to Sex, followed by The Expression of
the Emotions in Man and Animals.
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How Darwin conceived his idea

• He based his theory on fourth different evidences
• Direct Observation
• Biogeography
• Fossils
• Homologous Structures

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Direct Observation
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The first evidence is the direct observation. The
first object of his interest were the artificial
selection. He talked a lot about the intersection
of pigeons in order to obtain a thinner beak or
larger wings. In general, the artificial
selection, is the selection operated by man.
Voluntary (like the intersection between species)
or not.
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To explain the second case, we could talk about
the Biston Betularia.
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Biston betularia is a white moth, which lives in
Manchester. In the '800 a lot of factories were
born in this territory.
Slowly the white moth was replaced by the black
moth.
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Why? Because the trees, contaminated by smokes,
had become black, and the white moth, resting on
these trees, became targets for the raiders, and
because of the contrast it couldn't camouflage.
Slowly the darkest moth replaced the clearest
one, until the clear ones disappeared. When an
animal changes its colour to camouflage because
of any change in the environment or because of
the humans, we talk about industrial melanism.
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Biogeography
The second evidence is biogeography. Darwin had
noticed that in the same area, there were
different types of creatures and species.
Biogeography was the weapon to destroy the idea
of creationism. But the numerous examples of
different species in the same area, were only a
support to the evolution theory every single
animal is different, because they have different
needs, and different ways of surviving.
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Fossils
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The third evidence were fossils. During his
journey on the Beagle, Darwin studied a lot of
them. He discovered a substantial difference
between ancestral creatures and modern ones.
Unfortunately, this wasnt enough, because
nothing proved a gradual changing from a
primitive form. For this reason Darwin described
this evidence as little remarkable.
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Homologous Structures
The fourth evidence was the discover of a
homologous structure that was shared by every
single creature on Earth. The same starting DNA
sequence shows us the common origin of the
species.
As we can see in the image, different creatures
share the same basic structure. This structure
was particular of an animal called ancestral
tetrapode, or more precisely Silvanerpeton
Miripedes.
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An Incompleted Theory
Darwin lacked of precision, and in his theory he
didnt explain the origin of the variation that
permitted the evolution, but for that we have to
wait until the XX century, when Mendel would
analyse this matter.
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THE END