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Evolution (part5)
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All important topics releated to this chapter.

Shivam Sharma
Learning and teaching Biology, pursuing medical studies at TU.

Unacademy user
sir ji hmko ldka or ldki me gland payi jati h uske bare me pta krna h ldke or ldki me kon si pai jati h
  1. History of Evolution of Animals About 2000 million years before, the first cellular form of life appeared on the earth. Slowly these single- celled organisms evolved into multicellular organisms Invertebrates were formed around 500 mililon years before. Jawless fish must have evolved around 340 million years ago. At around the same time, fish with stout & strong fins, that could move on land & go back to water, must have appeared. The coelacanth or lobefins were the ancestors of modern day frogs & salamanders. These amphibians evolved into reptiles that lay thick- shelled eggs which do not dry up in the sun; this made the reptiles more successful than amphibians . . .

  2. In the next 200 million year or so, reptiles of different shapes and sizes dominated the earth Some of these land reptiles moved back to water to evolve into fish like reptiles (Ichthyosaurs) at around the same time (200 million years ago) . . . The land reptiles i.e., dinosaurs suddenly disappeared from the earth (mass extinction) about 65 million years ago, while some small sized reptiles continue to exist today like birds, crocodiles etc.

  3. When the reptiles disappeared, mammals started dominating the earth . The first mammal was like shrew There were mammals like horse, hippopotamus, rabbit, bear etc., in South America but when South America joined North America (in the continent drift), these animals were over- ridden by the fauna of North America Australian land mass remained isolated & the pouched mammals survived as there was no competition from any other mammal . .

  4. History of Evolution of Plants Some of the single celled organisms that appeared 2000 million years ago had pigments to capture solar energy and release oxygen, in the process of photosynthesis Bryophytes were the first plants to colonise lands (plants colonised the land much before animals) Sea weeds & few plants existed around 320 million years ago About 200 million years before, giant ferns (Pteridophytes) were present, but they all fell to form coal deposits slowly Herbaceous lycopods & arborescent lycopods evolved from Zosterophyllun of palaeozoic era Psilophyton is the common ancestor of horsetails, ferns & gymnosperms . . .

  5. Evolution of Man The common ancestor of apes and man is a primate Dryopithecus, that lived 15 million years ago .At the same time, another genus Ramapithecus also existed .Both Dryopithecus& Ramapithecus were hairy and walked like gorillas & chimpanzees; Dryopithecus was more ape like, but Ramapithecus was more man-like and is the forerunner of hominid evolution Chimpanzee fetus Chimpanzee aduit Human fetus Human adult

  6. . The human evolution is as follows: 1. Australopithecines . They probably lived 2 million years ago, in the east Africa grass lands They has brain capacity of 450- 600 cc . They hunted with stone weapons but essentially ate fruits. . 2. Homo habilis . This is called first human like being, the hominid . They had brain capacity of 650- 800 cc. . They probably did not eat meat 3. Homo erectus . Their fossils were found in java (Java man) in 1981 . They probably lived about 1.5 mya . They had a brain capacity of about 900cc . They probably ate meat.

  7. 3. Homo sapiens (Primitive man) Their fossils were found in near East & Central Asia He must have lived between 1,00,000- 40,000 years before Neanderthal man (Homo sapiens neanderthalensis) had a brain capacity of about 1400 cc. They used hides to protect the body & buried the dead They moved across continents & developed into distinct races . . . 4. Homo sapiens sapiens (Modern Man) . Homo sapiens sapiens arose during ice age between 75000- 10000 years ago He spread all over the globe & learned to cultivate plants & domesticate animals . .Pre- historic cave art developed about 18,000 years before . Agriculture started around 10,000 years back . Human settlements and cultivations started