Theory Of Evolution By Natural And Sexual Selection Essay, Research Paper

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. Indeed, Malthus? essay was written as a rebuttal to Godwin and Condorcet,

both of whom had argued that humans, under conditions of equality, were capable of infinite

progress and perfection. In the essay Malthus advanced the ?principle of population? to refute

that idea. Thus, Malthus? principle argued that ?human society could never progress toward

perfectibility because the population inevitably tends to increase beyond the means of

subsistence and is kept within the bounds of its resources only by misery, vice, and moral

restraint?.

Malthus? principle of population was based on the supposed differences in reproduction rates

between humans (who because of their status as ?top dog? in the animal kingdom reproduced

?geometrically?) and animals and plants (who could only increase ?arithmetically?, because they

served mankind as a means of sustenance). Darwin by contrast, shifted the center of attention

from humans to the animal and plant kingdoms, because he was impressed by their enormous

natural fertility, which was kept in check only by their own limited means of sustenance. By

shifting his perspective from mankind to animals and plants Darwin revealed the basic fallacy of

Malthus? argument. For if humans increased geometrically, animals and plants must also increase

at the same rate, and perhaps even more, because overall their natural rate of reproduction is

higher than that of mankind. Therefore, the struggle for existence, which to Malthus meant that

hardship and misery were the defining features of human life, to Darwin meant that every species

was in constant change, because nature favored the fittest through the process of natural selection.

Writing the Origin

Three and a half years have passed since Darwin read Malthus in October 1838 before he

finally sat down to write his ideas formally in May 1842. There are two main reasons for this

lengthy delay. First, throughout his life Darwin suffered from ill-health , which began to get acute

in 1837, and was particularly debilitating between 1838 and 1842. Second, during this time

Darwin had more pressing matters to attend to. In particular he was working on the book Coral

Reefs, papers for the Geological society, and work connected with the Zoology of the voyage of

the Beagle.

After completing the initial first sketch of 35 pages, he set out to write a larger and more thrall

sketch in 1844 (by the time he was finished the sketch numbered 230 pages). However, Darwin

still proceeded to write his ideas on evolution at a ?leisurely? pace, and not until 1856, when

urged by his colleague Lyell, did he start working on his magnum opus, the Origin. By June 1858

Darwin had completed about half of the book (on a scale three to four times as large as when it

was later published), when one day a nasty surprise awaited him.

On June 18, Darwin received a manuscript from the English naturalist Wallace. In the

manuscript Wallace described the theory of natural selection, and asked Darwin to comment on

his ideas. Darwin thought that the only honorable thing to do was to recommend the paper for

publication. Fortunately, for Darwin, Lyell suggested (and Wallace and Darwin accepted) that

both Wallace?s paper and extracts from Darwin?s sketch of 1844 be published simultaneously,

thus establishing the rights of both to priority. Interestingly, later on at the fiftieth anniversary

meeting of their joint publication, Wallace made it clear that although the idea of natural selection

came to both of them independently, Darwin?s contributions outweighed his by twenty to one

because Darwin had the credit of twenty years of priority and work.

The impact of the Origin

Finally, by 1859 Darwin finished writing the book, and on November 24 the Origin was first

published. The sales of the book exceeded everyone?s expectations (by 1876 16,000 copies were

sold in England alone), and the book?s impact was felt almost immediately. In the mid

nineteenth century English society where science was a popular topic of conversation, the book

competed with such dinner party topics as the Italian revolution. Even those who most bitterly

despised its content were quick to concede its importance.

Within the scientific community the book was creating a new paradigm that threatened to

disrupt the existing status-quo. The mood of the time is illustrated by August Weismann who

states: ?Darwin?s book fell like a bolt from the blue; it was eagerly devoured, and while it

excited in the minds of the younger students delight and enthusiasm, it aroused among the older

naturalists anything from cool aversion to violent opposition?. The young saw in Darwin an

opportunity for a new and freer philosophical universe. For instance, young biologists such as

Karl Pearson, referring to the beginning of time, were rejoiced when ?that wretched date BC

4004, was replaced by a long vista of millions of years of development?. However, the older

more professional scientists, objected to Darwin?s ideas on religious grounds. Before Darwin

published the Origin, science and religion existed in harmony. There was an understanding on

the part of religion that evolution was discredited by science. Now that men of science were

finally favorites of the church (just two centuries ago scientists such as Galileo were unfavorably

perceived by the church), it seemed foolish to give up this hard won peace for just another

evolutionary hypothesis.

Sexual Selection

Although Darwin discussed sexual selection in the Origin, the majority of the book (and hence

the primary importance) was devoted to natural selection. However, sexual selection played a far

more important role in Darwin?s The Descent of Man, and Selection in Relation to Sex

(henceforth referred to as the Descent), which was published on February 24, 1871. In the

Descent, sexual selection assumed an equal if not greater than role for the origin of species. For

Darwin sexual selection was not simply a subcategory of natural selection, but rather an alternative

or complementary mechanism of evolution. In addition, sexual selection, to a larger extent than

natural selection, shifts the focus of attention to one of the most significant and least appreciated

aspects of Darwin?s theory: ?the location of the struggle for existence lies primarily within

species rather than between species?. It is therefore inaccurate, from this point on, to refer to

Darwin?s theory as simply ?evolution by natural selection? (Darwin himself called the theory ?the

principle of evolution?).

The primary reason why Darwin ?abandoned? natural selection in favor of sexual selection was

the fact that natural selection could not properly explain either the evolution of man from the

animals or the differences between the sexes and races. The problem is that natural selection

assumes that only beneficial changes get preserved in future generations, whereas in reality ?the

races of man differ from each other and from their nearest allies amongst the animals , in certain

characters which are of no service to them in their ordinary habits of life?. By contrast, sexual

selection does not have to be useful for the purpose of adaptation to the environment, and it may

actually work against natural selection. Therefore, Darwin now argued that any features which are

not adaptive to the individual, and thus could not have been acquired through the process of

natural selection, must have been acquired through sexual selection.

The Reaction to the Descent

When the Descent was published in 1871 it became an immediate best-seller. The initial 2500

copies were sold almost instantaneously, and an additional 5000 copies were sold by the end of

the year. The book was exceedingly controversial at the time, dealing with perhaps the most

provocative evolutionary topic of all, the origin of man. In the book Darwin suggested that man

differed from animals in degree and not kind, and than proceeded to conclude that man descended

from a ?hairy, tailed quadruped, probably arboreal in its habits?. Surprisingly, the reaction to

the book was not as violent as one might have expected it to be, from Darwin?s previous

experience with the Origin. For instance, Hooker, who at that time found evolution discussed

everywhere relates the following: ?I dined out three times last weak, and at every table heard

evolution talked of as an accepted fact, and the descent of man with calmness?. However, the

picture painted by Hooker is rather deceptive, as the portrayed amiability was often a matter of

tone rather than of substance. People may not have been outraged, but neither were they placated.

Most of the critics choose to ridicule Darwin?s ideas rather than attack them head on. For

example, a typical response, published in the Athenaeum, went along the lines of: ?No man will

ever develop religion out of a dog or Christianity out of a cat?. Nevertheless, criticism was mostly

tempered with praise. A good example of this is provided in the Edinburgh Review which

carefully balanced displeasure with tribute: ?Mr. Darwin appears to us to be not more

remarkable for the acuteness and ingenuity of his powers of observation of natural phenomena,

than he is for the want of logical power and sound reasoning on philosophical questions?.

Therefore, while despised by some and adored by others Darwin?s ideas were quickly permeating

into the fabric of society.

Conclusion

Darwin left us a legacy which is greater than just the sum of his scientific work. Not only did

his theory of evolution illuminate our past, but also the present and the future were now possible

to interpret in ?Darwinian terms?. Probably more so than any other scientific theory, Darwin?s

theory of evolution, lends itself to various social interpretations known as ?social Darwinism?.

From the radical left to the radical right, Darwin?s theory has been adopted by such people as

Marx and Hitler, each of whom saw in it evidence for their own ideology. Alongside the likes

of Copernicus, Galileo, and Newton, Darwin has rightly earned his place in history as one of

the giants of the scientific revolution.

Bibliography

Bowler, Peter J. Charles Darwin the Man and His Influence. Basil Blackwell Ltd. London, 1990

Himmelfarb, Gertrude. Darwin and the Darwinian Revolution. Doubleaday & Company Inc. New

York, 1959

Lewontin, R. C. Darwin and Mendel-the Materialist Revolution. In: Neyman (ed.) The Heritage of

Copernicus. MIT Press. Cambridge, 1974.

R. C. Lewontin. Darwin and Mendel-the Materialist Revolution. In: Neyman (ed.) The Heritage of

Copernicus. MIT Press. Cambridge, 1974 p. 171

Ibid.

Gertrude Himmelfarb. Darwin and the Darwinian Revolution. Doubleaday & Company Inc. New York

1959. p. 168

Ibid. p. 33

Ibid. p. 43

Ibid. p. 53

Ibid. pp. 109-112

Ibid. p. 111

Ibid. p. 112

Ibid. p. 111

Ibid. p. 146

Ibid.

Ibid. p. 150

Peter J. Bowler. Charles Darwin the Man and His Influence. Basil Blackwell Ltd. London, 1990 p. 79

Himmelfarb. Darwin and the Darwinian Revolution. p. 152

Ibid. p. 154

Ibid.

Ibid.

Ibid. p. 155

Ibid.

Ibid. p. 157

Ibid.

Ibid.

Ibid. p.159

Ibid.

Ibid.

Ibid. p. 161

Ibid.

Ibid.

Ibid. pp. 189-190

Ibid. p. 280

Ibid. p. 282

Ibid.

Ibid. pp. 271-272

Ibid. pp. 299-300

Ibid. p. 346

Ibid. p. 342

Ibid. p. 336

Ibid.

Ibid. p. 337

Ibid. p. 338

Ibid. pp. 394-400