Paper No. : 08 Human Population Genetics Module : 31 Evolutionary History of Life Development Team Prof. Anup Kumar Kapoor Principal Investigator Department of Anthropology, University of Delhi Paper Coordinator Prof. Gautam K. Kshatriya Department of Anthropology, University of Delhi Content Writer Dr. Rajesh Kumar Gautam Dr. H.S.G.University, Sagar, MP Prof. A.Paparao Sri Content Reviewer Venkateswara University, Tirupati, Andhra Pradesh 1 Human Population Genetics Anthropology Evolutionary History of Life Description of Module Subject Name Anthropology Paper Name 08 Human Population Genetics Module Name/Title Evolutionary History of Life Module Id 31 2 Human Population Genetics Anthropology Evolutionary History of Life CONTENTS: 1. Learning outcomes: At the end of the module the reader will know Formation of earth Origin of life Theory of Divine or special creation Theory of Spontaneous generation Theory of Cosmozoic origin Theory of eternity Theory of Catastrophism Theory of Organic evolution Synthetic theory of evolution Pre-biotic chemistry First Evidence of Early Life Prokaryote to Eukaryotes Unicellular to Multicellular Photosynthesis Sexual Reproduction Geological Time Scale 3 Human Population Genetics Anthropology Evolutionary History of Life Evolutionary History of Life Introduction The life on the earth was originated by the process of complex physical and chemical reactions. When earth came into existence it was hot. The formation of earth crust has taken billion of years. By the combination of Oxygen and Hydrogen atom water was formed which is an essential part of life. Gradually, continuous thunder, lighting, raining has created environment for emergence of super matter having consciousness from unique combination of simple matter and energy. Atoms of carbon, nitrogen, hydrogen, oxygen, phosphorus and some other elements combined and given shape to macro molecules or polymers like RNA and DNA which have the capacity of replication and reproduction. There are many speculations about how and when life was originated. Scientific theories about origin and evolution life are based on facts and evidences. There are different theories about the origin of life. Before knowing about these theories, let we understand about the origin of universe because it is prerequisite for origin of life. In a book entitled “A Brief History of Time - From the big bang to black holes” the famous astronomer Stephen Hawking states that the universe was originated from an explosion of dark matter condensed at a place. This explosion was so powerful that the matter was spread in the universe and different celestial bodies like stars, planets, satellites were formed. In this process, by some of the matter the Sun its planets and satellite were formed. Our Sun and solar system is a small part of a family of many such stars (Sun) and their solar system which is called Galaxy. There are many such Galaxies in the Universe, according to an estimate; their approximate number is 170 billion (1.7 × 1011) galaxies in the observable universe ( Gott III et al. 2005). Each of these galaxies has billions of stars (sun). Small or dwarf galaxies have just a few thousand (103) stars, whereas the giants galaxies have one hundred trillion (1014) stars (Uson et al. 1990). Our own Galaxy called Milky Way is estimated to contain as high as one trillion stars (Odenwald 2014). After billions of years of Big Bang explosion the planet earth came into existence. After 1.0 to 3.5 billion of years of emergence of the planet earth, the earliest form of life was originated in the form of prokaryotic cells viz. virus and bacteria. Gradually, unicellular and multicellular organisms were evolved. The main theories about the origin of life on the earth are as follows: 4 Human Population Genetics Anthropology Evolutionary History of Life 1. Divine or special creation Theory 2. Spontaneous generation Theory 3. Theory of cosmozoic origin 4. Theory of eternity 5. Theory of Catastrophism 6. Theory of Organic evolution 7. Synthetic theory of evolution Divine or special creation Theory Divine or special creation theory is one of the oldest theories about the origin of life on the earth. According to this theory life was created by supernatural power. In every religious scripture there is mythology about origin of the Universe, Earth and Life. According to Hindu mythology the world was created by God Brahma. He is considered the God of creation. He created the whole universe. The first man was Manu and the first woman was Shradha. According to Islam and their holy Quran the Universe was created by Allah (God). Allah begins by stating that the universe and planet Earth took six "days" to create. (7:54) According to the Bible, the world was created within six days. On the first day, God made the heaven and the earth, on the second day; He separated the sky from the water, on the third day. He made the dry land and plants, on the fourth day. He formed the sun, the moon and the stars, on the fifth day. He made the fishes and the birds and on the sixth day, He formed the land animals and human beings. The first man, Adam and the first woman, Eve were created by God. Buddhists do not believe in any such divine or special creation. They have opinion that one does not need to know the origin of life in order to achieve enlightenment. Many Buddhists do not think about these kinds of questions as meaningful for the Buddhist goal of relieving oneself and others from suffering. Special creation theory lacks scientific evidences, on account of which it cannot be accepted. Theory of Spontaneous Generation (Abiogenesis or Autogenesis) Theory spontaneous generation or Abiogenesis or Autogenesis states that the life originated from 5 Human Population Genetics Anthropology Evolutionary History of Life nonliving things in a spontaneous manner. This concept was held by early Greek philosophers like Thales, Anaximander, Xanophanes, Empedocles, Plato, Aristotle, etc. In ancient Egypt, it was believed that the mud of the Nile could give rise to frogs, toads, snakes, mice and even crocodiles when warmed by the sun. Van Helmont (1577-1644) held that human sweat and wheat grains could give rise to organisms. He placed a dirty shirt in a receptacle containing wheat bran and found that after 21 days the gases from the shirt and wheat had formed living mice. Louis Pasteur, a French scientist took broths in a long necked flask and then he bent the neck of the flask. He boiled the broths in the flask to kill any microorganisms that might be present in them. The curved neck acted as a filter. If the flask with ‘swan neck’ (curved neck) is kept for months together, no life appeared, as the germ laden dust particles in the air were trapped by the curved neck which serves as filter. If the swan neck was broken off, the broths developed colonies of moulds and bacteria. Thus, he showed that the source of the micro-organisms for fermentation or putrefaction such as for milk, sugar and wine, etc., was the air and the organisms did not arise from the nutrient media. Thus Louis Pasteur (famous for “Germ Theory of Disease and Immunology”) finally disapproved abiogenesis and proved biogenesis. 6 Human Population Genetics Anthropology Evolutionary History of Life But according to biogenesis, life originated from pre-existing life which does not explain the origin of life. So abiogenesis is also disapprovedTheory of Cosmozoic Origin: This theory was proposed by Richter (1865). According to this theory, ‘protoplasm’ reached to the earth in the form of spores or germs or other simple particles from some unknown part of the universe with the cosmic dust, and subsequently evolved into various forms of life. Helmholz (1884) speculated that ‘protoplasm’ in some form reached the earth with falling meteorites. Arrhenius (1908, Nobel Prize Winner of 1903 in Chemistry) postulated the Panspermia Theory and stated that organisms existed throughout the universe and their spores etc., could freely travel through space from one star to the others. But, experiments have proved that Living matter cannot survive in the extreme cold, dryness and ultra-violet radiation hence the theory of cosmozoic origin was also discarded. This theory also fails to explain how the life originated, inspite, it advocated that the life had travelled from one to another planet. Theory of Eternity of Life: Theory of eternity states that there is no beginning of life and it will never end. It was as it is, and it would remain as it is. Some of the Indian religion for example: Jainism and Sikhism also have similar concept about the life. They believe that life is eternal, it has no beginning, it will never end. Theory of Catastrophism: Georges Cuvier (1769-1832), Father of “Modern Palaeontology” and Orbigney (1802- 1837) were the chief advocates of this theory. According to this theory, cataclysms (great destruction) or catastrophic (concerning disastrous event) revolution occurs upon earth from time to time which completely destroys all organisms (living beings). New organisms, then, suddenly form from inorganic matter. Each creation consists of life quite different from that of the previous one. In fact, this theory is merely a modification of theory of special creation. This theory is also not accepted. Theory of Organic Evolution 7 Human Population Genetics Anthropology Evolutionary History of Life Charles Darwin (1859) in his book entitled ‘Origin of Species’ stated how new species evolved from pre-existing ancestors by the process of natural selection, which operates through struggle for existence and survival of the fittest. And, in this way, only few individuals, who are best, got chance of reproduction. This process repeated in every generation, and after many generations the progeny of distinct characteristics evolve as a ‘new species’.