Charles Darwin and the Development and impact of the Theory of Evolution by Natural and Sexual Selection
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 Darwins 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.
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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. Darwins 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. Darwins 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 grandfathers books with admiration, later commented that his grandfather nticipated 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. Butlers 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 didnt 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 Lamarcks ideas. In 1828, at his fathers suggestion, Darwin entered Christs 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 Paleys works on theology, because of their logic. For the rest, however, he udged 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 Darwins theory). In addition, during his last year at Cambridge Darwin read two books which influenced him greatly, Herschels Preliminary Discourse on the Study of Natural Philosophy, and Von Humboldts 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 heory of evolution, but this is highly unlikely. At the time Darwins 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 natomy.
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 Darwins 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 nsight: 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 Darwins ideas took this turn. Furthermore, had the change occurred earlier, it would have shown up in Darwins 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, ost 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 Darwins 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 nvironment disturbs growth to produce random variation. H H 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 ccurate 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 ontemporary 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 ife, favorable variations would tend to be preserved, and unfavorable ones destroyed, the result being the formation of new species. By this chance encounter than, Darwins 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 Darwins theory was inspired by Malthus, Darwin diverged from Malthus in a critical way.
Darwins 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. . , 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 ubsistence 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 Wallaces paper and extracts from Darwins 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 ame to both of them independently, Darwins 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 everyones expectations (by 1876 16,000 copies were sold in England alone), and the books 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: Darwins 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 Darwins 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 erceived 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 Darwins 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 Darwins 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 Darwins theory as simply evolution by natural selection (Darwin himself called the theory the rinciple 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 election 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 Darwins 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 volution 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 Darwins 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 empered 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 Darwins 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 is 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, Darwins theory of evolution, lends itself to various social interpretations known as social Darwinism. From the radical left to the radical right, Darwins 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.