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For anything and everything on science from India | ||||||
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Dr Subodh Mahanti |
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What are we? Where do we come from? Where will
we go?. Nothing in biology makes sense except in the light of evolution. Theodosius Dobzhansky
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…My success as a man of science, whatever this may have amounted to, has been determined…by complex and diversified qualities… the love of science--unbounded patience in long reflecting over any subject--industry in observing and collecting facts -- and a fair share of invention as well as of common sense. With such moderate abilities as I possess it is truly surprising that I should have influenced to a considerable extent the belief of scientific men on some important points. Charles Robert Darwin in his Autobiography |
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Charles Darwin was born on February 12, 1809 at Shrewsbury, Shropshire, England. He was the fifth child of Dr. Robert Waring Darwin, (the son of physician scientist Erasmus Darwin) and his wife Susannah, the daughter of the pottery magnate Josiah Wedgwood. Darwin’s mother died in July 1817 when he was eight years of age and he was brought up by his sister, Caroline. Darwin was enrolled in Dr. Butler’s Shrewsbury School in 1818 at the age of nine. Darwin did not enjoy learning at school. For him, studies at his Shrewsbury School were a complete bore. Commenting on his school education Darwin wrote : “The school as a means of education to me was simply a blank. I learned absolutely nothing except by amusing myself reading and experimenting with chemistry”. However, he had an intense curiosity about natural world. Since his childhood he developed a thirst for discovery and adventure. He liked to collect unusual objects both living and non-living. Luckily for Darwin his home was surrounded by woods and wildlife. The River Severn flowed right by The Mount, his family home. There were always things to discover, places to explore. He took interest in the birds, fish and frogs found in the surrounding areas. He had a great fascination for collecting beetles, the rarer the species the better. At the age of 13, he had even described, in a scientific journal, a new species he had captured in the neighborhood. In his autobiography he describes a particular beetle hunt in detail : “I will give a proof of my zeal : one day on tearing off some old bark, I saw two rare beetles and seized one in each hand ; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth. Alas it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as well as the third one.” Darwin’s father once said to him “you care for nothing but shooting dogs, and rat-catching, and you will be a disgrace to yourself and all of your family.’ But Darwin commented, “…my father, who was the kindest man I ever knew and whose memory I love with all my heart, must have been angry and somewhat unjust when he used such words”. Darwin was influenced by his grandfather Erasmus Darwin (1731-1802), who was professionally a physician but he also established himself as a philosopher, naturalist and poet. Erasmus’ books Zoonomia : or the Laws of Organic Life and The Botanic Garden or Lovers of the Plants were famous. Erasmus had even offered a theory of evolution. He helped found the Lunar Society. Its members called “Lunatics”, met only during full moons, so that they find their way home in their horse-drawn carriages by bright moonlight. Among its members were inventor James Watt (1736-1819), the industrialist Matthew Boulton (1728-1809), the chemist Joseph Priestly (1733-1804) and potter Josiah Wedgwood (1730-95). Among Darwin’s other heroes were Georges Cuvier (1769-1832), the great zoologist, Karl von Linne or Carolus Linnaeus (1707-78), who classified thousands of plants and animals and Alexander von Humboldt (1769-1859), the explorer who traveled over much of the world making discoveries. In his early years Darwin developed interest in geology, zoology, botany and to a lesser extent in astronomy. Darwin’s interest in natural science did not mean much to his father because there were hardly any jobs in natural science. After seeing that his son was not doing good at school Dr. Robert Darwin sent Charles to the University of Edinburgh to be trained as a physician. While studying medicine Darwin continued to pursue his old hobbies – beetle collection, bird watching and so on. He made friends with a few other scholars older than himself but having interest in natural history. Robert Edmond Grant (1793-1874), a Professor of Zoology, took him on field trips. John Edmonston, a talented taxidermist, taught him how to mount birds and mammals specimen for collection. Darwin could not complete his studies in medicine, and it had to be abruptly terminated. As Darwin did not have the courage to face his father he took refuge with his maternal uncle Joshia Wedgwood II at the Wedgwood home called Maer Hall, at Staffordshire about 30 km from Shrewsbury. His maternal uncle who was very fond of him took him on tours of Scotland, Ireland, London and Paris much to the dislike of Darwin’s father. After seeing Darwin’s failure at becoming a physician, his father sent him to the Christ’s College, Cambridge in 1827 to study theology with a view to be ordained as a clergyman. But here again Darwin could not concentrate in his studies. Here he became attached with two scholars -- the Reverend Adam Sedgwick, a geology professor and the Reverend John Henslow, a botanist. The latter played a major role in shaping Darwin’s career. Of his Cambridge years, Darwin says, “…my time was wasted, as far as the academic studies were concerned as completely as at Edinburg and at school.” According to Darwin the only things he enjoyed in his studies at Cambridge were geometry, and the works of William Paley (1743-1805), a distinguished eighteenth century theologian. Darwin admired his beautiful logic and clear expression. Darwin returned home from Cambridge in 1831 without having completed his studies. With Professor Henslow’s encouragement Darwin had turned to be a promising naturalist and he had developed a specific interest in learning geology but he had no formal educational degree. At this stage something unexpected and dramatic appeared that was to change Darwin’s life and also the course of scientific discovery forever. It was a letter from Darwin’s favourite professor Henslow. Henslow was requested to help Robert FitzRoy, the captain of HMS Beagle to find a naturalist. Henslow himself wanted to join the expedition but after realizing the fact that he could not be away from his home, he offered the job to his brother-in-law, the Reverend Leonard Jenyns, a qualified naturalist. However, he also could not accept it as he was tied with Church responsibilities. After this Henslow wrote to Darwin urging him to take up the assignment. In a letter dated 24 August 1831 Henslow while explaining that the captain was seeking a young man to serve as ship’s naturalist not a `mere collector’ but also to be intelligent companion for the captain. He further wrote : “I consider you to be the best qualified person I know of who is likely to undertake such a situation… I state this not in the supposition of your being a finished naturalist, but as amply qualified for collection, observing and noting, anything worthy to be noted in Natural History.. Don’t put on any modest doubts or fears about your qualifications, for I assure you I think you are the very man they are in search of.” It may be noted here that though FitzRoy is mostly remembered as “Darwin’s Captain’, he made his mark as seaman, explorer, surveyor, mapmaker and meteorologist. He also became governor of New Zealand. His family name is from the French fils roy meaning “son of the king”. Robert FitzRoy graduated from the Royal Naval College at Portsmouth. He served on several vessels. In 1828, he was given the command HMS Beagle which had been sent to map the southern coasts of South America, including Patagonia and Tierra del Fuego. During his first command of Beagle (1828-1830) FitzRoy became interested in the Indian tribes of Tierra del Fuego and he brought four young members of the tribe including a nine-year old girl to England. His idea was to teach them English, and the plainer truths of Christianity, reading, gardening and “the use of common tools” and subsequently return them to their homeland. FitzRoy named the girl Fuegia Basket and the other three boys were called : York Minster, Boat Memory and Jemmy Button. One of the tribal youths, called Boat Memory died soon after reaching England. Among the other three Jemmy Button and Fuegia Basket made good progress in their learning and attracted the attention of the Press. After a few months of their stay in England FitzRoy wanted to take back these tribal youths to their homeland. The British Admiralty, however, did not show any interest in financing the project. But FitzRoy was determined to keep his word. Accordingly he took a year’s leave and arranged the money for hiring a ship. At this juncture one of his uncles came in his rescue by persuading the Admiralty to sponsor another surveying voyage for the Beagle. The British Admiralty commissioned Beagle for a five-year voyage with the purpose of mapping the coasts of Patagonia, Tierra del Fuego, Chile and Peru and then continue on around the globe to survey longitudes. Besides other normal crew FitzRoy wanted a naturalist preferably a young one to accompany him. It was a common practice to take a naturalist on a voyage of this kind. The main purpose of engaging a naturalist was to provide intelligent and gentlemanly company for the ship’s captain as British captains were expected to remain aloof from their hired crews. The post of naturalist was an upaid one. Darwin was very much interested in taking up the job but his father was not in its favour. He said that no man of common sense would approve such a foolish idea. His father thought that his son was trying to escape the responsibility of preparing a sensible career. He advised his son to forget about it and return to Cambridge to complete his studies to be qualified as clergyman. So young Darwin had no option other than to inform Henslow his inability to accept the offer. However, Darwin did not give up the hope of convincing his father. His only hope was that his father had said, “If you can find any man of common sense who advise you to go, I will give my consent”. Dawin went to his maternal uncle Josiah Wedgwood II (or uncle Josh as Darwin called him) to persuade him to convince Darwin’s father. Josiah Wedgwood II after listening Darwin carefully explained the risks involved in such a journey. And after seeing that Darwin was not only aware of the risks but he was perfectly willing to accept them, Josiah Wedgwood II decided to take up the matter with Darwin’s father. Darwin provided him a list of objections raised by his father. Josiah Wedgwood II wrote a letter answering every objection. In answer to the very first objection that the voyage would be “disreputable to (Darwin’s) character as a clergyman” Wedgwood replied, “The pursuit of Natural History, though certainly not professional, is very suitable to a clergyman”. Answering Dr. Robert Darwin’s objection that “it would be a useless undertaking” Wedgwood replied, “Looking upon Charles as a man of enlarged curiosity it (the voyage) affords him such an opportunity of seeing men and things as happens to few”. Darwin attached a separate note stating that he would accept his father’s decision on the subject as final and “he would never mention the subject again”. Instead of waiting for a reply Darwin and Josiah Wedgwood II went to Shrewsbury to meet Dr. Robert Darwin. Finally Dr. Robert Darwin consented and agreed to pay all Darwin’s expenses. The Beagle set sail on December 27, 1831. Darwin was only twenty two years old. There was no proper accommodation for Darwin. He had to share a cabin with the captain and there was virtually no room for keeping his instrument. Darwin wrote in his Journal: “The absolute want of room is an evil that nothing can surmount”. Darwin was plagued with sickness throughout the voyage. Darwin took four books with him for the journey – the Bible, a copy of Milton’s work, Alexander von Humboldt’s account of his exploration of Venezuela and the Orinoco basin and Volume One of Lyell’s Principle of Geology. The other two volumes of Lyell’s book was sent to him during the journey by Henslow. Darwin sent frequent reports on his observations to Henslow. Many of these reports were read by Henslow at meetings of the Philosophical Society of Cambridge. The Beagle visited many lands in the southern Pacific seas before returning to England in October 1836 via the Southern Cape of Africa in an effective circumnavigation of the globe. The ship visited amongst other places the Cape Varde Islands, Brazil, Argentina and Chile. After coming back from the voyage Darwin started working on his “Journal of Researches”, a work based upon this journal which he had kept during the voyage of the Beagle. This was published in 1839 and become an immediate’ success. The success of his first “literary child” always pleased Darwin more than that of any of his other books. Following the continued deterioration of his health Darwin moved to a country residence at Downe, Kent. Darwin lived a life of a country gentleman of independent means among his gardens, conservatories, pigeons and fowls. However, he conducted extensive experiments especially in variation and interbreeding. It was at Downe that most of his life’s work was done. Because of his continual health problem Darwin’s activities were mainly confined to writing books. The books written by Darwin are given at the end of the article. The first of his major geological works., The structure and Distribution of Coral Reefs”, was published in 1842. In this book Darwin presented a theory of the structure and mode of formation of coral reefs. Darwin’s theory was very different from the one existed them. However, his keen observation and accurate thinking made his theory acceptable to most of the geologists. In fact his theory is even now generally accepted among geologists. Darwin based on his observation of various facts of paleontology and biogeography, saw the possibility that species might not be immutable. But then he had no theory to work upon. However, he decided to apply the method adopted by Lyell in solving geological problems. Lyell had attacked geological problems by accumulating all applicable data in the absence of a working theory, in the hope that the sheer weight of facts might throw some light upon his problems. Darwin decided to adopt the same method to the species problem. Accordingly he started in July 1837 his work on variation in plants and animals, both under domestication and in nature. Darwin did not want to overlook any possible source of information. Thus he looked into personal observations and experiments, published papers of other biologists, conversations with breeders and gardeners, correspondence with biologists at home and abroad and so. Based on the analysis of accumulated facts from various sources Darwin realized that man’s success in producing useful varieties of plants and animals depended upon selections of desired variation for breeding stock. However, Darwin had no clue on how selection could be applicable to nature. But then he stumbled upon a theory to work upon. In October 1838, Darwin happened to read for sheer amusement “Malthus on Population”. The book written by Thomas Robert Matlhus (1766-1834) was first published anonymously in 1789. It was titled An Essay on the Principle of Population. The book was not about biology. In his book Malthus proposed that human population increase geometrically (e.g., 2,4,8,16…), while means to support them increase only arithmetically (e.g.1,2,3,4,5…). Accordingly natural selective forces such as overcrowding, disease, war, poverty and vice take over to remove those who are not fit and thus only the fittest survive. Darwin extended Malthus’s ideas and developed the idea of natural selection in species, a concept that is often referred to as “survival of the fittest”. The phrase “survival of the fittest” is often used synonymously with natural selection. The phrase is both incomplete and misleading. The word survival is only one component of selection and perhaps one of the less important ones in many populations. Aso, the word `fit’ is often confused with physically fit. Fitness, in an evolutionary sense, is the average reproductive output of a class of genetic variation in a gene pool . `Fit’ does not necessarily mean biggest, fastest or strongest. The theory of natural selection answers the question of who made the selection of what is to be evolved. The species that do survive in the competition for existence will go on to produce the next generation. The environment an organism lives in helps to determine which organisms survive and produce young, and which do not. Commenting on Malthus’s work, Darwin wrote : “In October 1938, that is fifteen months after I had began my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which goes on from long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species. Here, then, I had at last got a theory by which to work…” However, Darwin took four years to write the first outline of his theory. This is because he had to collect a great deal of more data. In 1842 Darwin produced a pencil draft of thirty-five pages. By 1844 Darwin enlarged this draft to 230 pages. Early in 1856 following the advice given by Lyell, Darwin began his work on a much larger scale with a view to prepare a full account of his ideas on the origin of species. But while Darwin was half on its way in completing his work a certain development took place which forced Darwin for early publication of his work. Alfred Russell Wallace (1823-1913) sent Darwin a short essay on the “Tendency of Varieties to Depart Indefinitely from the Original Type” with a request that if Darwin think it worthy he should forward it to Lyell for his comments. Darwin liked it very much because he recognized his own theory in it. Darwin sent Wallace’s paper to Lyell along with a covering letter. Darwin wrote: “Your words have come true with a vengeance – that I should be forestalled; if Wallace had my MS. Sketch written out in 1842, he could not have made a better short abstract”. At one point Darwin decided to withhold his own publication in favour of Wallace. However, Lyell and Joseph Hooker (1817-1911) had for years been familier with Darwin’s work on the transmutation of species. Lyell had read Darwin’s outline of 1842. Lyell and Hooker therefore suggested that Darwin write a short abstract of his theory and that it be published jointly with Wallace’s paper in the Journal of the Linnean Society. These papers appeared in that Journal in 1859 together with portion of a letter which Darwin had written to Asa Gray (1810-88), the great American botanist, in September 1857, in which Darwin set forth his views on natural selection and the origin of species. In his autobiography, Darwin wrote : “Early in 1856 Lyell advised me to write out my views pretty fully, and I began at once to do so on a scale three or four times as extensive as that which afterwards followed by my Origin of Species : yet it was only a abstract of the materials which I had collected, and I had got through about half the work on this scale. But my plans were overthrown far early in the summer of 1858. Mr. Wallace, who was in the Malaya Archipelago, sent me an eassy “On the tendency of varieties to depart indefinitely from the original type” and this eassay (arrived June 18th) contained exactly the same theory as mine. Mr. Wallace expressed the wish that if I thought well of this essay, I should send it to Lyell for perusal. The circumstances under which I consented at the request of Lyell and Hooker to allow an extract from my own M.S., together with a letter to Asa Gray, dated September 5, 1857 to be published at the same time with Wallace’s assay, are given in the Journal of the Linnean Society 1858 p. 45. I was at first very unwilling to consent, as I thought that Mr. Wallace might consider my doing so unjustifiable, for I did not then know how generous and noble was his disposition.” Following this Lyell and Hooker persuaded Darwin to prepare for early publication of a book on transmutation of species. Accordingly, he condensed the manuscript he had begun in 1856 to about one-third or even one-fourth its original size. The “Origin of Species” thus produced, was finally published in November 1859. The original title of the manuscript was “An Abstract of an Essay on the Origin of Species and Varieties through Natural Selection”. However, his publisher, John Murrey, persuaded Darwin to reduce this to On the Origin of Species, but Darwin insisted on keeping the words by means of Natural Selection as a kind of subtitle. Darwin also included on the title page the words Or the Preservation of Favoured Races in the Struggle for Life. Every copy of the original 1, 250-copies printed was sold on the VERY first day. Commenting on the success of Origin Darwin wrote : “The success of the `Origin’ may, I think, be attributed in large part to my having long before written two condensed sketches, and to my having finally abstracted a much larger manuscript, which was itself an abstract. By this means I was enabled to select the more striking facts and conclusions. I had, also, during many years followed a golden rule, namely that whenever a published fact, a new observation or thought came across me, which was opposed to my general results, to make a memorandum of it without fail at once; for I had found by experience that such facts and thoughts were far more apt to escape from the memory than favorable ones, owig to this habit, very few objections were raised against my views which I had not at least noticed and attempted to answer.” Darwin always referred to his Origin of Species as abstract. He wrote in its introduction: “This Abstract, which I now publish, most necessarily be imperfect. I cannot have given reference and authorities for my several statements, and I must trust to the reader reposing some confidence in my accuracy. No doubt errors will have crept in though I hope I have always been cautious in trusting to good authorities alone. I can have given only the general conclusions at which I have arrived, with a few facts in illustration, but which, I hope in most cases will suffice. No one can feel more sensible than I do of the necessity of hereafter publishing in detail all the facts, with references, on which my conclusions have been grounded ; and I hope in a future work to do this. For I am well aware that scarcely a single point is discussed in this volume on which facts cannot be adduced, after apparently leading to conclusions directly opposite to those at which I have arrived. A fair result can be obtained only by fully stating and balancing the facts and arguments on both sides of each question; and this cannot possibly be here done.” Darwin is mostly known for his hypothesizing the pattern of common descent and proposing a mechanism for evolution -- natural selection. Darwin’s theory of evolution is no longer just a theory -- an overwhelming amount of evidence has accumulated since Darwin. This it may be said that Darwin discovered a law as Copernicus, Galileo and Newton discovered laws -- natural laws. According to Darwin’s law life has come into being and exists and is depended on the process of natural selection. In Darwin’s theory of natural selection, new variants arrives continually with in population. Some of the variation may be neutral, but others help or hinder the organism in its struggle for survival. What Darwin did not know was the mode of inheritance. Today we know that the true mode of inheritance was discovered by Gregor Mendel through his experiments on hybrid peas. In fact Mendel mailed his paper to Darwin, but Darwin never opened it. The idea of evolution was not new to Darwin. Francis Bacon (1561-1626) in his book Novum organum (1620) noted the way in which species vary naturally from one generation to the next. Bacon observed that such natural variation could be used by the breeders of plants and animals to produce “many rare and unusual results:” Gottfried Wilhelm Leibniz (1646-1716), the German mathematician, speculated that species had changed because of difference in environmental conditions. Leibniz’s observation was based on his studies of fossils and the possible relationship between the extinct ammonites and living species such as the nautilus. The term evolution was first used in its modern biological context in 1826 by Robert Jameson. In the eighteenth century Georges Louis Lecrec, Comte de Buffon (1707-88) suggested that the North American bison might be descended from an ancestral variety of ox that had migrated there. Darwin’s grandfather Erasmus Darwin was convinced about the importance of evolution. However, Erasmus mistakenly though, that individual members of a species developed different characteristics during their, lifetime. And once acquired these advanced characteristics are passed on to their offsprings. Jean-Baptiste Lamarck (1744-1829) proposed a theory of evolution in 1809. He believed that species arose continually from nonliving sources. These species were initially very primitive, but increased in complexity over time due to some inherent tendency. Such type of evolution is called orthogenesis. Further Lamarck proposed that an organism’s acclimation to environment could be passed on to its offspring. For example Lamarck thought proto-giraffes stretched their necks to reach higher twigs and which caused their offspring to be born with longer necks. This is known as the inheritance of acquired characteristics. Lamarck also believed that species never went extinct, although they may change into newer forms. Lamarck’s ideas have been proved to be wrong. The observations made by a number of scientists implicitly included the concept of evolution and also the notion that species have evolved to fit their environments -- adaptation. Darwin offered an explanation of how evolution works – that is natural selection. Darwin’s theory of evolution made him many enemies among orthodox scientists and churchmen since beliefs in the Creation and divine guidance were threatened by Darwin’s revelations. Apelike cartoons of Darwin appeared in newspapers. Essays and sermons proliferated everywhere. Among the scientific opponents were Richard Owens, a renowned geologist at Oxford, Louis Agassiz at Harvard University in the USA and Adam Sedgwick, an old-school geologist from Cambridge. Darwin was not in a position to combat the furor, raised against his theory because of his continued illness. Moreover, he never recovered from the untimely death of his daughter Annie. The task of defending his theory was left to Thomas Henry Huxley (1825-95), a brilliant zoologist who became famous as “Darwin’s bulldog”. Huxley did his job quite well notably at the famous Oxford debate on June 30, 1860, where Huxley confronted Samuel Wilberforce, the powerful Bishop of Oxford. Besides Huxley and Wilberforce those present on the platform included : Darwin’s old teacher and anti evolutionist J.S. Huxley’s friends Joseph Hooker and John Lubbock, John Draper of New York University and Sir Benjamine Brodie, the Queen’s physician and President of the Royal Society. Seven hundred people were crowded into the University Museum where the debate was organized. In this debate Huxley instead of being ridiculed had won a wider interest and fair hearing for the new theories. Besides Huxley, Darwin’s prominent supporters were Charles Lyell and James Hooker. Lyell though convinced that Darwin was correct but he refused to come out squarely in favour of evolution in his public statements and writings before 1868 when he embraced the theory at the age of 71. Though the debate following the publication of the Origin of Species led to wide acceptance of Darwin’s theory among the scientists but it was far from being established during Darwin’s lifetime. The main reason for this was that Darwin could not explain how characteristics passed on from one generation to another and why there are variations from one individual to another. Variation is found among individuals who share the same parents. It is important to note that in the successive revisions to the Origin of Species Darwin himself backed away from natural selection. In the first edition of his Descent of Man Darwin wrote : “In the earlier editions of my “Origin of Species” I probably attributed too much to the action of natural selection or the survival of the fittest”. The first reason for Darwin’s retreat was the failure to explain the cause of variation, a key component in Darwin’s theory of natural selection. The second important reason was the enormous timescale required for evolution. In the second half of the nineteenth century the scientists believed that the Sun could not have been hot for more than a few millions years as there was no process known to scientists which could supply energy to keep the Sun shining for hundreds of millions of years required for the variety of forms of life on Earth to have evolved through small steps. Scientists of the twentieth century have established that the long time-scale required for evolution by natural selection is not a problem as the Sun has essentially remained unchanged for about 4.5 billion years, a more than sufficient time for evolution to happen. Today we know that the energy is supplied by nuclear processes. In the twentieth century biologists developed an understanding of genetics and how characteristics are inherited by offspring from their parents. As mentioned earlier it was Mendel who had first initiated work in this direction. By the 1940s Darwin’s theory of natural selection as spelt out in the first edition of the Origin of Species had become firmly established. So today, Darwin’s theory of evolution and common descent are considered facts by the scientific community. Though debates continue how various aspects of evolution work. For examples, all the details of pattern of relationship are not fully worked out. Evolution is regarded as the cornerstone of biology. While it is possible to do research in biology with little or no knowledge of evolution but then without evolution biology becomes a disperate sets of fields. Evolutionary explanations pervade all fields of biology and brings them together under one theoretical umbrella. The process of evolution can be summerised in three sentences: Genes (hereditary units) mutate. Individuals are selected. Population evolve. Evolution requires genetic variation. In order to continue evolution there must be mechanism to increase or create genetic variation and mechanism to decrease it . Mutation is a change in a gene. These changes are the source of new genetic variation. Natural selection operates on this variation. Natural selection favours traits or behaviours that increase a genotype’s inclusive fitness. The opportunity or natural selection to operate does not induce genetic variation to appear. Selection only distinguishes between existing variants. Selection merely favours beneficial genetic changes when they occur by chance — it does not contribute to their appearance. The potential for selection to act may long precede the appearance of selectable genetic variations. Natural selection does not have any foresight. It only allows organisms for adapt to their current environment. Structures or behaviours do not evolve for future utility. An organism adapts to its environment at each stage of its evolution. As the environment changes, new traits may be selected for. Darwin died on April 19, 1882 after prolong illness. Following a suggestion from of a group of members of British Parliament, he was accorded the honour of being buried in Westminster Abbey. (A burial place for English monarchs, outstanding statesmen etc). We would like to end this article by quoting Julian Huxley on Darwin. “Darwin’s work…put the world of life into the domain of natural law. It was no longer necessary or possible to imagine that every kind of animal or plant had been specially created, not that the beautiful and ingenious devices by which they get their food or escapes their enemies have been thought out by some supernatural power, or that there is any conscious purpose behind the evolutionary process. If the idea of natural selection holds good, then animals and plants and man himself have become what they are by natural causes, as blind and automatic as those which go to mould the shape of a mountain, or make the earth and the other planets more in ellipses round the sun. The blind struggle for existence, the blind process of heredity, automatically result in the selection of the best adopted types, and a steady evolution of the stock in the direction of progress… Darwin’s work has enabled us to see the position of man and of our present civilization in a truer light. Man is not a finished product incapable of further progress. He has a long history behind him, and it is a history not of a fall, but of an ascent. And he has the possibility of further progressive evolution before him. Further, in the light of evolution we learn to be patient. The few thousand years of recorded history are nothing compared to the million years during which man have been on earth, and the thousand million years of life’s progress. And we can afford to be patient when the astronomers assure us of at least another thousand million years ahead of us in which to carry evolution to new heights”. Books written by Charles Darwin 1. Voyage of the Beagle or Journal of Researches. London. 1839 Books on Darwin and His Theory 1. Allan, Mea, Darwin and His Flowers . New York, Taplinger, 1977 |
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