cx-ncert-theory-class12-chap06-evolution-en-part05

<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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>About 2000 million years ago (mya) the first cellular forms of life appeared on earth</p>
</li>
<li>
<p>The mechanism of how non-cellular aggregates of giant macromolecules could evolve into cells with membranous envelop is not known</p>
</li>
<li>
<p>Some of these cells had the ability to release $O_2$</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The reaction
could have been similar to the light reaction in photosynthesis where water is split with the help of solar energy captured and channelised by appropriate light harvesting pigments</p>
</li>
<li>
<p>Slowly single-celled organisms became multi-cellular life forms</p>
</li>
<li>
<p>By the time of 500 mya, invertebrates were formed and active</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Jawless fish probably evolved around 350 mya</p>
</li>
<li>
<p>Sea weeds and few plants existed probably around 320 mya</p>
</li>
<li>
<p>We are told that the first organisms that invaded land were plants</p>
</li>
<li>
<p>They were widespread on land when animals invaded land</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Fish with stout and strong fins could move on land and go back to water</p>
</li>
<li>
<p>This was about 350 mya</p>
</li>
<li>
<p>In 1938, a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct</p>
</li>
<li>
<p>These animals called lobefins evolved into the first amphibians that lived on both land and water</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>There are no specimens of these left with us</p>
</li>
<li>
<p>However, these were ancestors of modern day frogs and salamanders</p>
</li>
<li>
<p>The amphibians evolved into reptiles</p>
</li>
<li>
<p>They lay thickshelled eggs which do not dry up in sun unlike those of amphibians</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Again we only see their modern day descendents, the turtles, tortoises and crocodiles</p>
</li>
<li>
<p>In the next 200 millions years or so, reptiles of different
shapes and sizes dominated on earth</p>
</li>
<li>
<p>Giant ferns (pteridophytes) were present but they all fell to form coal deposits slowly</p>
</li>
<li>
<p>Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g.  Ichthyosaurs)</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The land reptiles were, of course, the dinosaurs</p>
</li>
<li>
<p>The biggest of them, i.e., Tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth</p>
</li>
<li>
<p>About 65 mya, the dinosaurs suddenly disappeared from the earth</p>
</li>
<li>
<p>We do not know the true reason</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The first mammals were like shrews</p>
</li>
<li>
<p>Their fossils are small sized</p>
</li>
<li>
<p>Mammals were viviparous and protected their unborn young inside the mother’s body</p>
</li>
<li>
<p>Mammals were more intelligent in sensing and avoiding danger at least</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>When reptiles came down mammals took over this earth</p>
</li>
<li>
<p>There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc</p>
</li>
<li>
<p>Due to continental drift, when South America joined North America, these animals were overridden by North American fauna</p>
</li>
<li>
<p>Due to the same continental drift pouched mammals of Australia survived because of lack of competition from any other mammal</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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>A Brief Account of Evolution</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Lest we forget, some mammals live wholly in water</p>
</li>
<li>
<p>Whales, dolphins, seals and sea cows are some examples</p>
</li>
<li>
<p>Evolution of horse, elephant, dog, etc., are special stories of evolution</p>
</li>
<li>
<p>You will learn about these in higher classes</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ <span style="color:blue">A Brief Account of Evolution</span> $\rarr$ 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 and Evolution of Man</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>About 15 mya, primates called Dryopithecus and Ramapithecus were existing</p>
</li>
<li>
<p>They were hairy and walked like gorillas and chimpanzees</p>
</li>
<li>
<p>Ramapithecus was more man-like while Dryopithecus was more ape-like</p>
</li>
<li>
<p>Few fossils of man-like bones have been discovered in Ethiopia and Tanzania (Figure 6.11)</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ <span style="color:blue">Origin and Evolution of Man</span></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 and Evolution of Man</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Two mya, Australopithecines probably lived in East African grasslands</p>
</li>
<li>
<p>Evidence shows they hunted with stone weapons but essentially ate fruit</p>
</li>
<li>
<p>Some of the bones among the bones discovered were different</p>
</li>
<li>
<p>This creature was called the first human-like being the hominid and was called Homo habilis</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ <span style="color:blue">Origin and Evolution of Man</span></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 and Evolution of Man</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The brain capacities were between 650-800cc</p>
</li>
<li>
<p>They probably did not eat meat</p>
</li>
<li>
<p>Fossils discovered in Java in 1891 revealed the next stage, i.e., Homo erectus about 1.5 mya</p>
</li>
<li>
<p>Homo erectus had a large brain around 900cc.<em>Homo erectus</em> probably ate meat</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ <span style="color:blue">Origin and Evolution of Man</span></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 and Evolution of Man</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>The Neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000-40,000 years back</p>
</li>
<li>
<p>They used hides to protect their body and buried their dead</p>
</li>
<li>
<p>Homo sapiens arose in Africa and moved across continents and developed into distinct races</p>
</li>
<li>
<p>During ice age between 75,000-10,000 years ago modern <em>Homo sapiens arose</em></p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ <span style="color:blue">Origin and Evolution of Man</span></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 and Evolution of Man</B></Primary></p>
<hr>
<main>
<div style='float: left; width:100%; text-align: left;font-size:23px'>
<ul>
<li>
<p>Pre-historic cave art developed about 18,000 years ago</p>
</li>
<li>
<p>One such cave paintings by Pre-historic humans can be seen at Bhimbetka rock shelter in Raisen district of Madhya Pradesh</p>
</li>
<li>
<p>Agriculture came around 10,000 years back and human settlements started</p>
</li>
<li>
<p>The rest of what happened is part of human history of growth and decline of civilisations</p>
</li>
</ul>
</div>
</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 $\rarr$ Biological Evolution $\rarr$ Mechanism of Evolution $\rarr$ Hardy - Weinberg Principle $\rarr$ A Brief Account of Evolution $\rarr$ <span style="color:blue">Origin and Evolution of Man</span></footer>