Charles Darwin2

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Charles Darwin2



Charles Darwin and the Development and impact of the
Theory of Evolution by Natural and Sexual Selection

Introduction

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 scale…”. 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 theorizer”. 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 animal and plant

life, favorable variations would tend to be preserved, and unfavorable ones destroyed, the result

being the formation of new species”. By this chance encounter than, Darwin’s theory was

provided with a rationale, and the “how” of evolution came to supplement the “why”.

It is important to note, that even though the crux of Darwin’s theory was inspired by Malthus,

Darwin diverged from Malthus in a critical way. Darwin’s debt to Malthus lies in the borrowing

of the concept of the “struggle for existence”. However, in general, what Malthus was concerned

about was not how the struggle for existence affected the quality of the population (i.e., he did not

suggest that in the struggle for existence the strong survive and the weak perish) but simply how it

limited its numbers.

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