A brief account of evolution

• About 2000 million years ago (mya) the first cellular forms of life appeared on earth.
• Some cellular form had the ability to release o2 and slowly single cell organisms became multicellular organisms.

Evolution of animals

• By the time of 500 mya, invertebrates were formed and active.
• Jawless fish probably evolved around 350 mya . fish with stout and strong fins could move on land and go back to water.
• In 1938, a lobe finned fish caught in south africa happened to be a coelacanth which evolved into first amphibians that lived on both land and water and water and these were the ancestors of modern day frogs and salamanders.
• The amphibians evolved into reptiles which lay thick shelled eggs which do not dry up on earth.
• The modern day descendants of reptiles are the turtles tortoises and crocodiles.
• In the next 200 million years or so, reptiles of different shapes and sizes dominated on earth.
• Some of the reptiles went back into water to evolve into fish like reptiles around 200 mya.
• The land reptiles were the dinosaurs and the biggest of them is tyrannosaurus rex was about 20 feet in height and had huge fearsome dagger like teeth.
• About 65 mya, the dinosaurs suddenly disappeared from the earth, some of them evolved into birds or might be killed by the climatic changes.
• The first mammals were like shrews and their fossils were small sized.
• Mammals were viviparous and protected their unborn young inside the mother’s body.
• Mammals dominated the earth when the population of reptiles came down.

Evolution of plants :-

• Plants invaded land before animals.
• Bryophytes originated earlier than vascular plants like pteridophytes and gymnosperm.
• The first vascular plants developed in silurian period.
• Sea weeds and few plants exited around 320 million years ago ( mya)

Bryophytes

Pteridophytes

Gymnosperm

angiosperm

Origin And evolution of man :-

Dryopithecus and ramapithecus –

• About 15 mya. Primates called dryopithecus and ramapithecus were existing.
• They were hairy and walked like gorillas and chimpanzees.
• Ramapithecus was more man-like while dryopithecus was more ape-like.
• Few fossils of ma-like bones have been discovered in ethiopia and tanzania.
• These revealed hominid features leading to the belief that about 3-4 mya, man-like primates walked in eastern africa.

Australopithecus-

• About two mya, australopithecines probably lived in east african grasslands.
• They hunted with stone weapons but essentially ate fruit.
• Some of the bones among the bones discovered were different.
• They were intermediate between apes and man.

Homo habilis :-

• The brain capacities were between 650-800 cc.
• They probably did not eat meat.
• They were the makers of stone tools.

Homo erectus-

• About 1.5 mya, homo erectus arose.
• Homo erectus had a large brain around 900cc.
• Homo erectus probably ate meat.

Neanderthal man-

• The neanderthal man with a brain size of 1400cc lived in near east and central asia between 1,00,000-40,000 years back.
• They used hides to protect their body and buried their dead.

Homo sapiens or modern man –

• Arose in africa and moved across continents.
• During ice age between 75,000- 10,000 years ago modern homo sapiens arose.
• Prehistoric cave art developed about 18,000 years ago.