Origin Theories
Several theories regarding the ‘origin of life’ have been put forward.
1. Special Creation Theory :
According to this theory universe was created by God in six days. This theory has been published in Bible.
According to this theory—
First day—Earth and heaven were created.
Second day—Sky was created.
Third day—Dry earth and plants were created.
Fourth day—Sun, moon and stars were created.
Fifth day—Birds and fishes were created.
Sixth day—Man and all other animals were created.
2. Spontaneous generation theory : As the name indicates, according to this theory every living thing was created spontaneously from the inanimate substances. This is also known as theory of abiotic genesis.
3. Biogenesis : This theory was given by Francessco and confirmed by Lazzaro in 1765. According to this theory life can only be originated from life.
4. Modern Theory : Haeckel proposed this theory and Oparin elaborated it. According to this theory origin of life was a gradual process not a sudden process. This theory was given by Oparin in 1922. Life was originated from inorganic substances.
Chemical Evolution : In this, changes in atmosphere took place. Certain elements like Carbon, Hydrogen, Nitrogen, Phosphorus, Sulphur, Nickel, Aluminium, Iron, Copper, Silicon, etc. were formed.
Inorganic substances like Carbondioxide, Ammonia, Hydrogen, Water etc. were formed.
Organic substances like methane, ethane, carbohydrates, ketones etc. were formed.
Complex substances like carbohydrates, fats, proteins etc. were formed. Finally the formation of nucleoproteins took place. J.B.S. Haldane referred these materials as hot soup.
Organic Evolution referred these materials as hot soup.
Organic Evolution : The process of gradual and orderly change which has led to the development of present day complex living organisms pre-existing single ones is called organic evolution.
Whatever theories are there, the processes have similarities—
Similarities : 1. Environment provides energy and material to all living beings.
2. All living beings reproduce their own kind.
3. Proteins and nucleic acids are synthesized by all living organisms.
4. All living beings have genetic code.
Millers and Urey have carried out many experiments concerning organic evolution. Their experiments showed that C, H, O, and N are the important biologically elements.
Fossils
Fossils are remnants of plants and animals of ancient times found in rocks or in soil. The study of fossils is known as palaeontology. This branch was established in 1800 by George Cuvier.
Now the question arises, how fossils were formed.
1. Bones, teeth, shells of animals were preserved.
2. Hard parts of plants and animals were pressed and preserved.
3. Decayed parts of plants and animals were preserved in minerals.
4. Complete body of animals was frozen and preserved in snow for thousands of years.
Many types of fossils have been discovered by the scientists. These are petrified fossils such as bones, shells, teeth, tree trunks etc. Leaves wings of insects were found as mould fossils. Unaltered fossils were found covered in snow. Bodies of mammoths and rhinoceros were found. Print and compressed fossils have also been discovered.
Age of the rocks have been found out by studying fossils. Two methods namely Uranium-lead method and Radioactive carbon method have been used to determine the age of fossils. Study of fossils have helped a lot to understand evolution.
Geological Time Scale
The age of the earth, rocks etc. can be calculated by using geological time scale method. According to this study the time scales are—
Age of the earth—4.6 billion years.
According to the age of earth the total time has been divided into following eras.
1. Archaeozoic era.
2. Proterozoic era.
3. Paleozoic era.
4. Masozoic era.
5. Cenozoic era.
In these eras following are the important events.
1. Archaeozoic era : First life and unicellular organisms about 1500 million years ago appeared.
2. Proterozoic era : In this era about 925 million years ago primitive life and marine invertebrates appeared.
3. Paleozoic era : Ancient life, fishes, amphibians came into existence.
Cambrian period : Ordovician period, silurian period, devorian period, carboniferos period, permian period all come under Paleozoic era. This era existed from 550 million years to 215 million years back.
4. Mesozoic era : This is also known as age of reptiles. It contains Triassic period, Jurassic period and Cretaceous period. This existed from 190 million yeas to 120 million years. All kinds of reptiles existed in this era.
5. Cenozoic era : This was the age of mammals, birds and modern insects. It has tertiary period and quaternary period. It existed from 70 million years to 1 million years. Recent epoch which showed rise of modern man is only 20,000 years old.
Theories of Organic Evolution
There have been two theories namely—
(a) Theory of natural selection
(b) Theory of pangenesis.
Theory of Natural Selection : This theory is based on six prepositions namel—
(i) Enormous fertility in the organisms.
(ii) Struggle for existence.
(iii) Variation and their inheritance.
(iv) Survival of the fittest.
(v) Variation in the organisms due to changing environment.
(vi) Origin of new species.
Theory of natural selection was given by Charles Darwin. It had certain criticisms. These were corrected in New-Darwin theory.
(b) Theory of Pengenesis : This was mainly based on Mendals ideas i.e. based on hereditary characters.
Many evidences have been given for evolution. These evidences are Morphological evidences, homology and analogy, vestigal organs, Embryological evidence etc. Many scientists like Charles Robert, Haeckel Von Beer etc. contributed a lot in bringing theories of evolution.
Human Evolution
The sequence of human evolution has been as follows—
(i) Primitive ape lived about 40 million years ago.
(ii) Home eracius lived about 5,00,000 years ago.
(iii) Home Neanderthal man lived some 1,50,000 years ago.
(iv) Cromagnon man lived some 50,000 years ago.
(v) Modern man is about 25,000 years old.
Human Evolution
Anthropoid : A group of primates in which only monkeys, apes and humans were included.
Hominid : A member of the family hominid containing humans and their direct ancestors known only by the fossils record.
Hominoid : A member of a superfamily having humans and the great apes.
Mammal : Members of vertebrates having hair and mammary glands.
Molecular Clock : The ideas that the rate at which mutation changes accumulate in certain types of genes is constant over time and is not involved in adaptation to the environment.
Neanderthal : Hominid who lived during the last age in Europe and the Middle East; these people made stone tools and lived together in a kind of society.
Primate : Animal that belongs to the order primate. It includes, monkeys, apes and humans.
Proconsul : A forest-dwelling primate with some characteristics of living apes.
Prosimian : A group of primates that includes lemurs and tarsiers and may resemble the first primates to have evolved.
Marsupials : Mammals that carry their youngs in a pouch. e.g. Kangaroos and Opossums.
Placentals : Mammals in which the foetus is attached to the wall of the womb and nourished by an organ called placenta.
Primates : Highest order of animals including monkeys, apes and men.
Dryopithecus : A twenty million years old first fossils record in tracing the evolution of man. It was first discovered in France in 1856. Dryopithecus showed the characteristics of both monkeys and apes.
Australopithecus : Australopithecus or “southern ape” is considered as a connecting link betwen ape and man. Its fossils were found in South Africa by Prof. Raymond Dart in 1925.
Homo erectus : Homo erectus or the first true man is the descendent of Australopithecus. He is also known as African ape man or Java man. Its fossil was discovered by E. Dobois in Java.
Homo Neanderthalensis : Homo nenderthalensis or Neanderthal man is the descendent of Homo erectus. The fossils of Homo neanderthalensis were found in Neanderthal valley of Germany in 1856.
Cro-Magnon Man : The Cro-Magnon man is considered as the forefather of modern man.
Homo habilis : Hominid of 2 million years ago; possibly a direct ancestor of modern humans.
Homo sapiens : Homo sapiens is the descendant of Cro-Magnon man. He is considered as the most advanced form of primate. According to H.L. Shapiro, the future man will be taller, baldy and with more developed body. His name has been given as Homo futuris.
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