cx-ncert-theory-class12-chap06-evolution-en-part01

<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>Intoduction</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Evolutionary Biology is the study of history of life forms on earth</p>
</li>
<li>
<p>What exactly is evolution? To understand the changes in flora and fauna that have occurred over millions of years on earth, we must have an understanding of the context of origin of life, i.e., evolution of earth, of stars and indeed of the universe itself</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px"><span style= "color: blue;">Introduction</span> $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Intoduction</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>What follows is the longest of all the construed and conjectured stories</p>
</li>
<li>
<p>This is the story of origin of life and evolution of life forms or biodiversity on planet earth in the context of evolution of earth and against the background of evolution of universe itself.</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px"><span style= "color: blue;">Introduction</span> $\rarr$ Origin of Life  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>When we look at stars on a clear night sky we are, in a way, looking back in time</p>
</li>
<li>
<p>Stellar distances are measured in light years</p>
</li>
<li>
<p>What we see today is an object whose emitted light started its journey millions of year back and from trillions of kilometres away and reaching our eyes now</p>
</li>
<li>
<p>However, when we see objects in our immediate surroundings we see them instantly and hence in the present time</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Therefore, when we see stars we apparently are peeping into the past</p>
</li>
<li>
<p>The origin of life is considered a unique event in the history of universe</p>
</li>
<li>
<p>The universe is vast</p>
</li>
<li>
<p>Relatively speaking the earth itself is almost only a speck</p>
</li>
<li>
<p>The universe is very old – almost 20 billion years old</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Huge clusters of galaxies comprise the universe</p>
</li>
<li>
<p>Galaxies contain stars and clouds of gas and dust</p>
</li>
<li>
<p>Considering the size of universe, earth is indeed a speck</p>
</li>
<li>
<p>The Big Bang theory attempts to explain to us the origin of universe</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>It talks of a singular huge explosion unimaginable in physical terms</p>
</li>
<li>
<p>The universe expanded and hence, the temperature came down</p>
</li>
<li>
<p>Hydrogen and Helium formed sometime later</p>
</li>
<li>
<p>The gases condensed under gravitation and formed the galaxies of the present day universe</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>In the solar system of the milky way galaxy, earth was supposed to have been formed about 4.5 billion years back</p>
</li>
<li>
<p>There was no atmosphere on early earth</p>
</li>
<li>
<p>Water vapour, methane, carbondioxide and ammonia released from molten mass covered the surface</p>
</li>
<li>
<p>The UV rays from the sun brokeup water into Hydrogen and Oxygen and the lighter $H_2$ escaped</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Oxygen combined with ammonia and methane to form water, $CO_2$  and others</p>
</li>
<li>
<p>The ozone layer was formed</p>
</li>
<li>
<p>As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans</p>
</li>
<li>
<p>Life appeared 500 million years after the formation of earth, i.e., almost four billion years back</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Did life come from outerspace? Some scientists believe that it came from outside</p>
</li>
<li>
<p>Early Greek thinkers thought units of life called spores were transferred to different planets including earth</p>
</li>
<li>
<p>‘Panspermia’ is still a favourite idea for some astronomers</p>
</li>
<li>
<p>For a long time it was also believed that life came out of decaying and rotting matter like straw, mud, etc</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>This was the theory of spontaneous generation</p>
</li>
<li>
<p>Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life</p>
</li>
<li>
<p>He showed that in pre-sterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Spontaneous generation theory was dismissed once and for all.
However, this did not answer how the first life form came on earth</p>
</li>
<li>
<p>Oparin of Russia and Haldane of England proposed that the first form of life could have come from pre-existing non-living organic molecules (e.g</p>
</li>
<li>
<p>RNA, protein, etc.) and that formation of life was preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic constituents</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>He created electric discharge in a closed flask containing $CH_4$ , $H_2$ , $NH_3$  and water vapour at $8000^{\circ}C$</p>
</li>
<li>
<p>He observed formation of amino acids</p>
</li>
<li>
<p>In similar experiments others observed, formation of sugars, nitrogen bases, pigment and fats</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Analysis of meteorite content also revealed similar compounds indicating that similar processes are occurring elsewhere in space</p>
</li>
<li>
<p>With this limited evidence, the first part of the conjectured story, i.e., chemical evolution was more or less accepted</p>
</li>
<li>
<p>We have no idea about how the first self replicating metabolic capsule of life arose</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The first non-cellular forms of life could have originated 3 billion years back</p>
</li>
<li>
<p>They would have been giant molecules (RNA, Protein,Polysaccharides, etc.)</p>
</li>
<li>
<p>These capsules reproduced their molecules perhaps</p>
</li>
<li>
<p>The first cellular form of life did not possibly originate till about 2000 million years ago</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ 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>Origin of Life</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>These were probably single-cells</p>
</li>
<li>
<p>All life forms were in water environment only</p>
</li>
<li>
<p>This version of a biogenesis, i.e., the first form of life arose slowly through evolutionary forces from non-living molecules is accepted by majority</p>
</li>
<li>
<p>However, once formed, how the first cellular forms of life could have evolved into the complex biodiversity of today is the fascinating story that will be discussed below.</p>
</li>
</ul>
</div>
</main>
<hr>
<footer style= "font-size:18px">Introduction $\rarr$ <span style="color:blue">Origin of Life</span>  $\rarr$ Evolution of Life Forms - A Theory $\rarr$ What are the Evidences for Evolution $\rarr$ What is Adaptive Radiation $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ Origin and Evolution of Man</footer>