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Darwin’s
Theory
by Federico Brovelli
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.
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.
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.
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.
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.
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.
Darwin’s 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.
How Darwin conceived his idea
He based his theory on fourth different evidences
 Direct Observation
 Biogeography
 Fossils
 Homologous Structures
Direct Observation
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.
To explain the second case, we could talk about
the Biston Betularia.
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.
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.
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.
Fossils
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 wasn’t enough, because nothing
proved a gradual changing from a primitive
form. For this reason Darwin described this
evidence as “little remarkable”.
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.
An Incompleted Theory
Darwin lacked of
precision, and in his
theory he didn’t 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.
THE END