Theory Of Evolution

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Theory of Evolution



CHARLES DARWIN AND THE THEORY OF EVOLUTION


It is commonly thought today that the theory of evolution originated from Darwin in the
nineteenth century. However, the idea that species mutate over time has been around for
a long
time in one form or another. Therefore, by Darwin's time the idea that species change
from one
type into another was by no means new, but was rejected by most because the
proponents of
evolution could not come up with a satisfactory mechanism that would explain this change.


The most influential evolutionary theories prior to Darwin were those of Lamarck and
Geoffroy St. Hilaire, developed between 1794 and 1830. Lamarck suggested that species
evolve
through the use or disuse of particular organs. In the classic example a giraffe that
stretches its
neck slightly to reach higher leaves will gain in neck length, and this small gain would be
passed
on to its offspring. Geoffroy, on the other hand suggested that the change was
discontinuous,
large in magnitude, and occurred at the production of offspring. However, these theories
of
evolution were based on a priori explanations that offered no demonstrated mechanism.

Darwin's theory of evolution differs in that it is based on three easily verified observations.
First, individuals within a species vary from one another in morphology, physiology, and
behavior. Second, variation is in some part heritable so that variant forms have offspring
that
resemble them. Third, different variants leave different number of offspring. Darwin than
proceeded to elaborate on the mechanism of evolution by suggesting that in the universal
struggle
for life, nature selects those individuals who are best suited (fittest) for the struggle, and
these
individuals in turn reproduce more than those who are less fit, thus changing the
composition of
the population. In addition to natural selection, Darwin also suggested that species also
evolve
through the complementary process of sexual selection. According to Darwin, in sexual
selection,
one gender of a species develops a preference for individuals of the other gender who
possess
certain features. The individuals who possess these features will than have a reproductive
advantage over others, resulting in a greater number of offspring, and thus, again, a
change in the
composition of the population. Therefore, it was Darwin who made the theory of evolution
feasible by providing the mechanisms of natural and sexual selection.

Darwin's Formative Years

Charles Darwin was born in England in 1809 and belonged to a wealthy and respectable
family. His grandfather, Erasamus Darwin, was a noted botanical expert in his day who
published
two important books, Zoonomia, and the Botanic Garden. In these books, Erasamus
speculated
about various evolutionary ideas that were dismissed as too radical (i.e., the nose of the
swine has
become hard for the purpose of turning up the soil in search of insects and roots). Darwin
who in
his youth read his grandfather's books with admiration, later commented that his
grandfather
anticipated the views and erroneous grounds of opinion of Lamarck. Nevertheless,
Erasamus
may have unconsciously influenced Darwin in preparing the way for evolution by natural
selection.

In 1818, at the age of 9, Darwin entered the Shrewsbury school, which was ran by Dr.
Butler.
Darwin later recalled that nothing could have been worse for the development of my mind
than
Dr. Butler's school, as it was strictly classical, nothing else being taught , except a little
ancient
geography and history. The school as a means of education to me was simply a blank. He
was
removed from the school in 1825, and was sent to Edinburgh to study medicine. There he
studied
for two years before deciding that he didn't like medicine. But before he left Edinburgh, he
was
introduced for the first time to the theories of Lamarck. According to Darwin at the time he
was
not very impressed with Lamarck's ideas. In 1828, at his father's suggestion, Darwin
entered
Christ's College in Cambridge to become a clergyman. To Darwin a good education meant
instruction in the methods and logic of thought. Therefore, Just about the only thing he
enjoyed
studying there was Paley's works on theology, because of their logic. For the rest,
however, he
judged Cambridge to be just as much a waste of time as Edinburgh and Shrewsbury.

Nevertheless, in his spare time at Cambridge, Darwin became interested in various
scientific
endeavors, and became acquainted with and influenced by the scientific ideas of Henslow,
Sedgwick, and Whewell (ironically Sedgwick later became a bitter opponent of Darwin's
theory). In addition, during his last year at Cambridge Darwin read two books which
influenced him greatly, Herschel's Preliminary Discourse on the Study of Natural
Philosophy, and Von
Humboldt's Personal Narrative of Travels to the Equinoctial Regions of the New Continent.
Darwin later confessed that these books inspired in him a burning zeal to add even the
most
humble contribution to the noble structure of Natural Science.

In 1831 Darwin graduated from Cambridge, and as he was pondering his future he
received a
proposal to join a scientific expedition that would survey the southern coast of Tierra del
Fuego.
Darwin accepted the proposal, and sailed from England aboard the famed Beagle on
December,
27, 1831. His job was to collect and catalogue new species so that they could be sent back
for
further research in England. It is commonly thought that Darwin used the voyage to test
his
theory of evolution, but this is highly unlikely. At the time Darwin's interests were purely
geological as can be seen by his correspondence with his sister. For instance, writing
about the
fossils which he discovered he said, All the interest which I individually feel about these
fossils
is their connection with the geology of the Pampas. Furthermore, Darwin himself
confessed that he could not have appreciated the significance of his findings while on the
voyage, because he
lacked the necessary training in dissection and drawing as well as the knowledge of
comparative
anatomy. It was only much later when Darwin returned from the voyage, and when the
fossils
were identified by Owen, that Darwin began to examine them as zoological, rather then
geological, phenomena.

The voyage turned out to be very productive for Darwin, who upon his return in 1836
began to work on the conversion of the diary, which he kept during the voyage, into a
journal suitable for publication. The Journal was first published in 1839 under the title
Journal and Remarks, as
Volume III of the Narrative of the Surveying Voyages of H.M.S. Adventures and Beagle.
However, enough people thought that Darwin's work was sufficiently important to warrant
a
separate publication, and in 1845 a second edition was published under the name Journal
of
Research into the Natural History and Geology of the Countries Visited during the Voyage
of
(H.M.S. Beagle Round the World (henceforth referred to as the Journal). Darwin Discovers
Evolution

It appears to be that only sometime in 1837 did Darwin first start to entertain the idea of
evolution seriously. The proof for this lies in the notebook which he kept from July 1837 to
February 1838. In particular, the following statement from the notebook provides valuable
insight: In July opened first notebook on transmutation of species. Had been greatly struck
from about the previous March on character of South American fossils, and species of
Galapagos
Archipelago. These facts (especially latter), origin of all my views. Therefore, it must have
been
at this time that Darwin's ideas took this turn. Furthermore, had the change occurred
earlier, it
would have shown up in Darwin's writings in the Journal, which, more than half completed
by
March, shows no trace of it. Overall, with the notable exception of the idea of natural
selection,
most of what Darwin later wrote in On the Origin of Species by Means of Natural
Selection, or
the preservation of Favoured Races in the Struggle for Life (henceforth referred to as the
Origin),
was already sketched in that notebook. It is important to note that Darwin's thinking at this
point was still distinctly teleological in character. He still believed that God had instituted
the laws governing reproduction to maintain species in a state of perfect adaptation to
their environment. Only after his full appreciation of the struggle for existence did he come
to believe that a changed environment disturbs growth to produce random variation.

Curiously, Darwin asserts that in originating his theory of evolution he was trying to follow
Baconian principles, that is collect facts before theorizing. Specifically, in his autobiography
he
states "After my return to England it appeared to me that by following the example of Lyell
in
Geology, and by collecting all facts which bore in any way on the variation of animals and
plants
under domestication and nature, some light might perhaps be thrown on the whole
subject. My
first notebook was opened in July 1837. I worked on true Baconian principles, and without
any
theory collected facts on a wholesale scaleÓ. However, as his notebooks of the time amply
demonstrate, he was speculating boldly from the very beginning in favor of evolution. In
addition, Darwin himself at other times admitted his dislike for the Baconian method. For
instance in one of his correspondences he wrote "How odd it is that any one should not
see that
all observation must be for or against some view if it is to be of any service". And
elsewhere,
"No one could be a good observer unless he was an active theologian". Therefore, a more
accurate description of his method would be, "inventing a theory and seeing how many
classes of
facts the theory could explain". Darwin Discovers Natural Selection During his early
theorizing Darwin was fixated upon the whys of evolution. He contemplated such questions
as "Why is life short ? Why does the individual die, and why do species die ? Why does
nature put so high a premium on generation ? And why does generation have the twofold
character of perpetuation and variation". It seems that apart from the occasional reference
to adaptation, Darwin ,at that time, almost deliberately tried to avoid the contemporary
theories of the mechanics of evolution.

Notwithstanding, Darwin, sooner or later, had to confront the question of how evolution
occurred. Amusingly, he happened to stumble upon the answer quite accidentally. In his
spare
time Darwin enjoyed reading various books rather aimlessly, for amusement. One of these
books,
which he read in October 1838, happened to be Malthus' Essay on the Principle of
Population.
As Darwin himself later related, Malthus' description of the struggle for existence in human

society immediately suggested to him that under the competitive conditions of

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