Slide 1 : Charles Robert Darwin Great English Naturalist
Slide 2 : Biography Early life Charles Robert Darwin was born in Shrewsbury, Shropshire, England on 12 February 1809 at his family home, the Mount.[10] He was the fifth of six children of wealthy society doctor and financier Robert Darwin, and Susannah Darwin (née Wedgwood). He was the grandson of Erasmus Darwin on his father’s side, and of Josiah Wedgwood on his mother’s side. Both families were largely Unitarian, though the Wedgwoods were adopting Anglicanism. Robert Darwin, himself quietly a freethinker, made a nod toward convention by having baby Charles baptised in the Anglican Church, but Charles and his siblings attended the Unitarian chapel with their mother. The eight year old Charles already had a taste for natural history and collecting when he joined the day school run by its preacher in 1817. That July, his mother died. From September 1818, he joined his older brother Erasmus attending the nearby Anglican Shrewsbury School as a boarder The seven-year-old Charles Darwin in 1816, one year before his mother’s death.
Slide 3 : Education Darwin spent the summer of 1825 as an apprentice doctor, helping his father treat the poor of Shropshire, before going with Erasmus to the University of Edinburgh. He found lectures dull and surgery distressing, so neglected his medical studies. He learned taxidermy from John Edmonstone, a freed black slave who had accompanied Charles Waterton in the South American rainforest, and often sat with this "very pleasant and intelligent man".
In Darwin’s second year he joined the Plinian Society. He learnt classification of plants, and assisted with work on the extensive collections of the University Museum. This neglect of medical studies annoyed his father, who shrewdly enrolled him in a Bachelor of Arts course at Christ’s College, Cambridge to qualify as a clergyman and get a good income as an Anglican parson Darwin had to stay at Cambridge until June. He studied Paley's Natural Theology which made an argument for divine design in nature, explaining adaptation as God acting through laws of nature. Christ’s College, Cambridge
Slide 4 : Journey of the Beagle He find a letter from Henslow recommending Darwin as a suitable (if unfinished) naturalist for the unpaid position of gentleman’s companion to Robert FitzRoy, the captain of HMS Beagle, which was to leave in four weeks on an expedition to chart the coastline of South America. His father objected to the planned two-year voyage, regarding it as a waste of time, but was persuaded by his brother-in-law, Josiah Wedgwood, to agree to his son’s participation
Slide 5 : Inception of Darwin’s evolutionary theory While still a young man, Charles Darwin joined the scientific elite When the Beagle returned on 2 October 1836, Darwin was already a celebrity in scientific circles . He wrote his first paper, showing that the South American landmass was slowly rising, and with Lyell’s enthusiastic backing read it to the Geological Society of London on 4 January 1837. On 17 February 1837, Darwin was elected to the Council of the Geographical Society and Lyell's presidential address presented Owen’s findings on Darwin’s fossils, stressing geographical continuity of species as supporting his uniformitarian ideas. By mid-March, Darwin was speculating in his Red Notebook on the possibility that "one species does change into another" to explain the geographical distribution of species both living and extinct.[
Slide 6 : Overwork, illness, and marriage Darwin finished writing his Journal around 20 June 1837 just as Queen Victoria came to the throne, but then had its proofs to correct. Darwin’s health suffered from the pressure. On 20 September 1837, he had “an uncomfortable palpitation of the heart", and his doctors urged him to "knock off all work" and live in the country for a few weeks. He included mankind in his speculations from the outset, and on seeing an orangutan in the zoo on 28 March 1838 noted its child-like behavior. On 11 November, he returned to Maer and proposed to Emma, once more telling her his ideas. On 29 January 1839, Darwin and Emma Wedgwood were married at Maer in an Anglican ceremony .He died 19 April 1882 (aged 73)Down House, Downe, Kent, England Charles chose to marry his cousin, Emma Wedgwood In October 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere 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
Slide 7 : Works Darwin was a prolific author, and even without publication of his works on evolution would have had a considerable reputation as the author of The Voyage of the Beagle, as a geologist who had published extensively on South America and had solved the puzzle of the formation of coral atolls, and as a biologist who had published the definitive work on barnacles. While The Origin of Species dominates perceptions of his work, The Descent of Man, and Selection in Relation to Sex and The Expression of Emotions in Man and Animals had considerable impact, and his books on plants including The Power of Movement in Plants were innovative studies of great importance, as was his final work on The Formation of Vegetable Mould Through the Action of Worms As "Darwinism" became widely accepted in the 1870s, amusing cariacatures of him with an ape or monkey body symbolised evolution.
Slide 8 : Modern evolutionary synthesis The modern evolutionary synthesis is a union of ideas from several biological specialties which forms a sound account of evolution. This synthesis has been generally accepted by most working biologists. The synthesis was produced over about a decade (1936–1947), and the development of population genetics (1918–1932) was the stimulus. This showed that Mendelian genetics was consistent with natural selection and gradual evolution. The synthesis is still, to a large extent, the current paradigm in evolutionary biology.
Julian Huxley invented the term, when he produced his book, Evolution: The Modern Synthesis (1942). Other major figures in the modern synthesis include R. A. Fisher, Theodosius Dobzhansky, J.B.S. Haldane, Sewall Wright, E.B. Ford, Ernst Mayr, Bernhard Rensch, Sergei Chetverikov, George Gaylord Simpson, and G. Ledyard Stebbins.
The modern synthesis solved difficulties and confusions caused by the specialisation and poor communication between biologists in the early years of the twentieth century. Discoveries of early geneticists were difficult to reconcile with gradual evolution and the mechanism of natural selection. The synthesis reconciled the two schools of thought, while providing evidence that studies of populations in the field were crucial to evolutionary theory. It drew together ideas from several branches of biology that had become separated, particularly genetics, cytology, systematics, botany, morphology, ecology and paleontology
Slide 9 : Adaption An adaptation is a characteristic of an organism that has been favored by natural selection and increases the fitness of its possessor.[1][2] The concept is central to biology, particularly in evolutionary biology. Adaptation is the change in living organisms that allow them to live successfully in an environment. Adaptations enable living organisms to cope with environmental stresses and pressures. Adaptations can be structural, behavioral or physiological. Structural adaptations are special body parts of an organism that help it to survive in its natural habitat (e.g., skin colour, shape, body covering). Behavioural adaptations are special ways a particular organism behaves to survive in its natural habitat (e.g., phototropism). Physiological adaptations are systems present in an organism that allow it to perform certain biochemical reactions (e.g., making venom, secreting slime, homeostasis).
Adaptations are traits that have been selected by natural selection. The underlying genetic basis for the adaptive trait did not arise as a consequence of the environment; the genetic variant pre-existed and was subsequently selected because it provided the bearer of that variant some advantage. The first experimental evidence of the pre-existing nature of genetic variants was provided by Luria and Delbrück who developed fluctuation analysis, a method to show the random fluctuation of pre-existing genetic changes that conferred resistance to phage by the bacterium Escherichia coli
Slide 10 : Genetic drift In population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly, but often compound over time. More precisely termed allelic drift, the process of change in the gene frequencies of a population due to chance events determine which alleles (variants of a gene) will be carried forward while others disappear. It is distinct from natural selection, a non-random process in which the tendency of alleles to become more or less widespread in a population over time is due to the alleles' effects on adaptive and reproductive success.[1]
Especially in small populations, the statistical effect of sampling error (during reproduction) on certain alleles from the overall population may result in an allele (and the biological traits that it confers) becoming more common or rare over successive generations. This is evolutionary change; often a particular gene either becomes fixed in the population, or goes extinct. Given enough time, speciation follows as genetic drift builds up.
The concept was first introduced by Sewall Wright in the 1920s. There is debate over the relative significance of genetic drift. Many scientists consider it to be one of the primary mechanisms of biological evolution[1]. Others, such as Richard Dawkins (borrowing from Ronald Fisher), consider genetic drift important (especially in small or isolated populations), but much less so than natural selection.
Slide 11 : Gene flow In population genetics, gene flow (also known as gene migration) is the transfer of alleles of genes from one population to another.
Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population.
There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, as greater mobility of an individual tends to give it greater migratory potential. Animals tend to be more mobile than plants, although pollen and seeds may be carried great distances by animals or wind.
Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. It is for this reason that gene flow strongly acts against speciation, by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species.
Example: If a field of genetically modified corn is grown alongside a field of non-genetically modified corn, pollen from the former is likely to fertilize the latter
Slide 12 : Mutation In biology, mutations are changes to the nucleotide sequence of the genetic material of an organism. Mutations can be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation, chemical mutagens, or viruses, or can be induced by the organism, itself, by cellular processes such as hypermutation. In multicellular organisms with dedicated reproductive cells, mutations can be subdivided into germ line mutations, which can be passed on to descendants through the reproductive cells, and somatic mutations, which involve cells outside the dedicated reproductive group and which are not usually transmitted to descendants. If the organism can reproduce asexually through mechanisms such as cuttings or budding the distinction can become blurred. For example, plants can sometimes transmit somatic mutations to their descendants asexually or sexually where flower buds develop in somatically mutated parts of plants. A new mutation that was not inherited from either parent is called a de novo mutation. The source of the mutation is unrelated to the consequence, although the consequences are related to which cells are affected.
Mutations create variation within the gene pool. Less favorable (or deleterious) mutations can be reduced in frequency in the gene pool by natural selection, while more favorable (beneficial or advantageous) mutations may accumulate and result in adaptive evolutionary changes. For example, a butterfly may produce offspring with new mutations. The majority of these mutations will have no effect; but one might change the color of one of the butterfly's offspring, making it harder (or easier) for predators to see. If this color change is advantageous, the chance of this butterfly surviving and producing its own offspring are a little better, and over time the number of butterflies with this mutation may form a larger percentage of the population.
Slide 13 : Natural selection Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common, due to differential reproduction of genotypes. Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes. The phenotype's genetic basis, the genotype associated with the favorable phenotype, will increase in frequency over the following generations. Over time, this process may result in adaptations that specialize organisms for particular ecological niches and may eventually result in the emergence of new species. In other words, natural selection is the mechanism by which evolution may take place within a given population of organisms.
Natural selection is one of the cornerstones of modern biology. The term was introduced by Charles Darwin in his groundbreaking 1859 book The Origin of Species[1] in which natural selection was described by analogy to artificial selection, a process by which animals with traits considered desirable by human breeders are systematically favored for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of inheritance; at the time of Darwin's writing, nothing was known of modern genetics. Although Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work would lie in obscurity until the early 20th century. The union of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is termed the modern evolutionary synthesis. Although other mechanisms of molecular evolution, such as the neutral theory advanced by Motoo Kimura, have been identified as important causes of genetic diversity, natural selection remains the single primary explanation for adaptive evolution
Slide 14 : Speciation Speciation is the evolutionary process by which new biological species arise. There are four modes of natural speciation, based on the extent to which speciating populations are geographically isolated from one another: allopatric, peripatric, parapatric, and sympatric. Speciation may also be induced artificially, through animal husbandry or laboratory experiments. Observed examples of each kind of speciation are provided throughout Natural speciation All forms of natural speciation have taken place over the course of evolution, though it still remains a subject of debate as to the relative importance of each mechanism in driving biodiversity. [2]
There is debate as to the rate at which speciation events occur over geologic time. While some evolutionary biologists claim that speciation events have remained relatively constant over time, some palaeontologists such as Niles Eldredge and Stephen Jay Gould have argued that species usually remain unchanged over long stretches of time, and that speciation occurs only over relatively brief intervals, a view known as punctuated equilibrium
Slide 15 : The End Prepared by Ravi & Sourav
Class-10th A
2008-09
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