The origin of the Earth – II, Biological evolution, Origin and Evolution of Man

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Biological Evolution

  • The essence of Darwinian Theory about evolution is natural selection. The rate of appearance of new forms is linked to the life cycle or the life span.
  • Microbes that divide fast have the ability to multiply and become millions of individuals within hours.
  • A colony of bacteria (Type A) growing on a given medium has built- in variation in terms of ability to utilize a feed component.
  • A change in the medium composition would bring out only that part of the population (type B) that can survive under the new conditions.
  • In due course of time this variant population outgrows the others and appears as new species. This would happen within days.
  • For the same thing to happen in a fish or fowl would take millions of years as life spans of these animals are in years.
  • Hence, there must be a genetic basis for getting selected and to evolve.
  • Another way of saying the same thing is that some organisms are better adapted to survive in an otherwise hostile environment. Adaptive ability is inherited. It has a genetic basis. Fitness is the end result of the ability to adapt and get selected by nature.

A Brief Account of Evolution

  • About 2000 million years ago (mya) the first cellular forms of life appeared on earth.
  • The mechanism of how non-cellular aggregates of giant macro molecules could evolve into cells with membranous envelop is not known.
  • Some of these cells had the ability to release O2. The reaction could have been similar to the light reaction in photosynthesis where water is split with the help of solar energy captured and channelized by appropriate light harvesting pigments.
  • Slowly single-celled organisms became multi-cellular life forms. By the time of 500 mya, invertebrates were formed and active. Jaw less fish probably evolved around 350 mya. Sea weeds and few plants existed probably around 320 mya.
  • We are told that the first organisms that invaded land were plants. They were widespread on land when animals invaded land.
  • Fish with stout and strong fins could move on land and go back to water. This was about 350 mya. These animals called lobe fins evolved into the first amphibians that lived on both land and water. These were ancestors of modern day frogs and salamanders.
  • The amphibians evolved into reptiles. They lay thick-shelled eggs which do not dry up in sun unlike those of amphibians. Again we only see their modern day descendants, the turtles, tortoises and crocodiles.
  • In the next 200 million years or so, reptiles of different shapes and sizes dominated on earth. Giant ferns (pteridophytes) were present along with reptiles but they all fell to form coal deposits slowly.
  • Some of these land reptiles went back into water to evolve into fish like reptiles probably 200 mya (e.g. Ichthyosaurs).
  • The land reptiles were, of course, the dinosaurs. The biggest of them were Tyrannosaurus and ultrasaurus.
  • About 65 mya, the dinosaurs suddenly disappeared from the earth. We do not know the true reason. Some say climatic changes killed them. Some say most of them evolved into birds. The truth may live in between. Small sized reptiles of that era still exist today.
  • The first mammals were like shrews. Their fossils are small sized. Mammals were viviparous and protected their unborn young inside the mother’s body.
  • Mammals were more intelligent in sensing and avoiding danger at least. When reptiles came down mammals took over this earth.

Origin and Evolution of Man

  • 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 man-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. They were probably not taller than 4 feet but walked up right.
  • Two mya, Australopithecines probably lived in East African grasslands. Evidence shows they hunted with stone weapons but essentially ate fruit.
  • Some of the bones among the bones discovered were different. This creature was called the first human-like being the hominid and was called Homo habilis. The brain capacities were between 650-800cc. They probably did not eat meat.
  • The Neanderthal man with a brain size of 1400 cc 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 arose in Africa and moved across continents and developed into distinct races. During ice age between 75,000-10,000 years ago modern Homo sapiens arose.
  • Pre-historic cave art developed about 18,000 years ago. Agriculture came around 10,000 years back and human settlements started. The rest of what happened is part of human history of growth and decline of civilizations.

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