cx-ncert-theory-class12-chap06-evolution-en-part03

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>What is Adaptive Radiation</B></Primary></p>
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<p>He realised that there were many varieties of finches in the same island</p>
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<p>All the varieties, he conjectured, evolved on the island itself</p>
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<p>From the original seed-eating features, many other forms with altered beaks arose, enabling them to become insectivorous and vegetarian finches (Figure 6.5)</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ <span style="color:blue">What is Adaptive Radiation</span> $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>What is Adaptive Radiation</B></Primary></p>
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<p>This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation</p>
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<p>Darwin’s finches represent one of the best examples of this phenomenon</p>
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<p>Another example is Australian marsupials</p>
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<p>A number of marsupials, each different from the other (Figure 6.6) evolved from an ancestral stock, but all within the Australian island continent</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ <span style="color:blue">What is Adaptive Radiation</span> $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>What is Adaptive Radiation</B></Primary></p>
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<p>When more than one adaptive radiation appeared to have occurred in an isolated geographical area (representing different habitats), one can call this convergent evolution</p>
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<p>Placental mammals in Australia also exhibit adaptive radiation in evolving into varieties of such placental mammals each of which appears to be ‘similar’ to a corresponding marsupial (e.g., Placental wolf and Tasmanian wolf-marsupial)(Figure 6.7)</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ <span style="color:blue">What is Adaptive Radiation</span> $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
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<p>Evolution by natural selection, in a true sense would have started when cellular forms of life with differences in metabolic capability originated on earth</p>
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<p>The essence of Darwinian theory about evolution is natural selection</p>
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<p>The rate of appearance of new forms is linked to the life cycle or the life span</p>
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<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
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<p>Microbes that divide fast have the ability to multiply and become millions of individuals within hours</p>
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<p>A colony of bacteria (say A) growing on a given medium has built-in variation in terms of ability to utilise a feed component</p>
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<p>A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
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<p>In due course of time this variant population outgrows the others and appears as new species</p>
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<p>This would happen within days</p>
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<p>For the same thing to happen in a fish or fowl would take million of years as life spans of these animals are in years</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
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<p>Here we say that fitness of B is better than that of A under the new conditions.Nature selects for fitness</p>
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<p>One must remember that the so-called fitness is based on characteristics which are inherited</p>
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<p>Hence, there must be a genetic basis for getting selected and to evolve</p>
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<p>Another way of saying the same thing is that some organisms are better adapted to survive in an otherwise hostile environment</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
<hr>
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<p>Adaptive ability is inherited</p>
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<p>It has a genetic basis</p>
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<p>Fitness is the end result of the ability to adapt and get selected by nature</p>
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<p>Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution (Figures 6.7 and 6.8)</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
<hr>
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<p>Even before Darwin, a French naturalist Lamarck had said that evolution of life forms had occurred but driven by use and disuse of
organs</p>
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<p>He gave the examples of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks</p>
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<p>As they passed on this acquired character of elongated neck to succeeding generations, Giraffes, slowly, over the years, came to acquire long necks</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
<hr>
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<p>Nobody believes this conjecture any more</p>
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<p>Is evolution a process or the result of a process? The world we see, inanimate and animate, is only the success stories of evolution</p>
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<p>When we describe the story of this world we describe evolution as a process</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
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<div style='float: left; width:100%; text-align: left;font-size:23px'>
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<p>On the other hand when we describe the story of life on earth, we treat evolution as a consequence of a process called natural selection</p>
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<p>We are still not very clear whether to regard evolution and natural selection as processes or end result of unknown processes</p>
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<p>It is possible that the work of Thomas Malthus on populations influenced Darwin</p>
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<p>Natural selection is based on certain observations which are factual</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
<hr>
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<p>For example, natural resources are limited, populations are stable in size except for seasonal fluctuation, members of a population vary in characteristics (infact no two individuals are alike) even though they look superficially similar, most of variations are inherited etc</p>
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<p>The fact that theoretically population size will grow exponentially if everybody reproduced maximally (this fact can be seen in a growing bacterial population) and the fact that population sizes in reality are limited, means that there had been competition for resources</p>
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<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>

<p><Success style = "float: center; text-align: center; font-size:30px"><B>Evolution</B></Success></p>
<p><Primary style = "float: center; text-align: center; font-size:26px"><B>Biological Evolution</B></Primary></p>
<hr>
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<p>Only some survived and grew at the cost of others that could not flourish</p>
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<p>The novelty and brilliant insight of Darwin was this: he asserted that variations, which are heritable and which make resource utilisation better for few (adapted to habitat better) will enable only those to reproduce and leave more progeny</p>
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</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ <span style="color:blue">Biological Evolution</span> $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>