Origin and evolution of life

In a Nutshell

1. Big Bang :

i) The universe came into existence with an explosion called the “Big Bang” which occurred about 15 billion years ago. Then, formation of our solar system consisting of the sun and planets took place.

ii) The earth may have originated about 4.6 billion years ago.

2. Theories of the origin of life :

i) Protobiogenesis means the origin of life on the earth.

ii) Life came into existence from the non-living substances of the primordial earth about 3 billion years ago. The following are the theories of the origin of life.

Theory	Proposer	Details
Special Creation	Spanish Monk Father Sudrez proposed the theory of special creation.	The living beings on the earth were specially created by God or by some supernatural power.
Cosmozoic or Panspermia theory	Richter in 1865, proposed this theory.	Life on the earth came from a distant planet in the form of spores or micro-organisms called cosmozoa or Panspermia.
Spontaneous generation or Abiogenesis or Auto bio-genesis	This theory was initially put forth by Greek philosophers in 600 B.C. and later supported by Aristotle.	Life originated from non-living material spontaneously, without any interruption. Louis Pasteur finally disproved this theory.
Bio-genesis	According to the theory of bio-genesis	Living organisms are always produced from pre-existing living forms by reproduction and not from non-living or lifeless matter.

3. Modern self assembly theories :

According to this theory, origin of life on the earth occurred due to inherent property of self-organization or self assembly shown by chemical molecules.

4. Chemical evolution of life or self-assembly theory of origin of life :

This theory is also called biochemical origin of life or molecular evolution. This theory was formulated by haeckel, but developed by oparin and Haldane.

5. Oparin-Haldane theory of chemical evolution :

Oparin and Haldane proposed the theory of chemical evolution of life. According to this theory, the entire process of chemical evolution can be divided into the following steps :

i) Origin of earth and its primitive atmosphere

ii) Formation of ammonia, water and methane

iii) Synthesis of simple organic compounds

iv) Formation of complex organic compounds

v) Formation of nucleic acid

vi) Formation of protobiont or pre-cells

vii) Formation of first cell

viii) Biological evolution

6. Concervate theory of Oparin :

In 1983, oparin performed an experiment to demonstrate the formation of protein molecules during chemical evolution. This was named as coacervates. He suggested that coacervates gave rise to the first cell-like forms, i.e. “protobionts” or “eobionts”.

7. Micro-sphere theory of Sydney Fox :

Dr. Syndney Fox studied Oparin’s coacervate theory and performed the experiments to show that the amino acids polymerized into proteinolds. These later formed micro-spheres.

8. Coacervates and the micro-spheres were the fore-runners of the first form of life on this earth.

9. Urey and Miller performed an experiment in support of chemical evolution.

10. Organic Evolution :

Organic evolution is defined as a slow, gradual, continuous and irreversible change through which the present day complex forms have descended from their simple pre-existing forms of the past.

11. Theories of Organic Evolution :

i) Darwin’s theory of origin of species by Natural selection :

Darwin’s theory of organic evolution by natural selection is based on the following principles :

a) Over production or enormous fertility or prodigality of production.

b) Struggle for existence.

c) Variations and heredity.

d) Survival of the fittest or Natural selection.

e) Origin of new species.

ii) Hugo de Vries theory of Mutation theory:

The main features of de Vries mutation theory are as follows:

a) The new species originate suddenly due to mutations.

b) Mutations are the raw material for organic evolution.

c) Mutations occur frequently among the members of naturally breeding populations or species.

d) Mutations are heritable changes that can establish new species.

e) Mutations are random, taking place in all directions.

f) Unsuitable mutations are destroyed by Natural selection.

iii) Modern synthetic theory of evolution:

Scientists like Dobazansky, Mayer, J. Huxley, Simpson, Stebbins, Fisher, Haldane, Sewall Wright, etc. Are the main architects of the modern synthetic theory of evolution?

12. Genetic Populations (Mendelian Populations) :

Mendelian population is a group of similar individuals interbreeding among themselves and occupying a geographical area is called genetic population.

13. Gene pool:

Gene pool is the sum total of genes of all individuals of interbreeding population.

14. Gene frequency:

Gene frequency is the proportion of an allele in the gene pool as compared with other alleles at the same locus.

15. Concepts of the modern synthetic theory:

It consists of three main concepts, viz. Genetic variations, Natural selection and isolation.

i) Genetic variation:

The change in gene and gene frequencies is called genetic variation. The following factors cause genetic variation in populations.

a) Gene mutation: Sudden changes in the chemical makeup of a gene are called “Gene Mutation” or point mutation.

b) Gene Flow: The transfer of genes between populations that differ genetically from one another is called gene flow.

c) Genetic recombination: Sexual reproduction and crossing over are two important means of genetic recombination. It is responsible for spreading the variations in the population.

d) Genetic drift: Any alteration in allele frequency in the natural population by pure chance is called genetic drift. It is also called Sewall Wright effect.

e) Chromosomal aberrations: It refers to the structural alterations in a chromosome causing changes in the chromosome.

ii) Natural Selection :

Natural selection is the fundamental and the only operating mechanism of evolution.

· Industrial Melanism: The industrial melanism is an example of natural selection in action. Peppered moth showed this phenomenon which was studied by Kettle well.

· In peppered moth, called Biston betularia, Natural selection established a phenotype trait according to the changing environmental conditions.

iii) Isolation :

· Separation of a single population into several sub-units is called isolation.

· No interbreeding occurs between isolated groups thereby preventing genetic exchanges.

· The isolating mechanisms are of two types, namely, geographical isolation and reproductive isolation.

· Types of isolation mechanisms / classification of isolating mechanisms :

a) Pre-matting or Pre-zygotic isolating mechanisms :

i) Habitat isolation

ii) Seasonal isolation

iii) Ethological isolation

iv) Mechanical isolation

b) Post-matting or post-zygotic isolating mechanisms :

i) Gamete mortality

ii) Zygote mortality

iii) Hybrid sterility

16. Evidences for evolution:

There are four evidences, viz., paleontological evidences, comparative anatomical evidences, embryological evidences and molecular or genetic evidences which support the theory of evolution.

i) Paleontological evidences :

· The fossils in various forms are paleontological evidences.

· Primitive forms of organisms are obtained from the lower strata while advanced forms are obtained from the upper strata of the surface of earth.

· These are sound, reliable and direct evidences in favor of evolution.

· Fossils are formed in the sedimentary rocks, amber, volcanic gas, ice, peat bogs and soil, etc.

· Types of fossils are actual remains, modules, casts, etc.

· Connecting links are also obtained in the form of fossils. Seymouria, Ichthyostega and Archaeopteryx are some well known and important connecting links.

ii) Comparative anatomical evidences :

· Homologous organs: Organs which are structurally similarly similar but functionally dissimilar.

· Analogous organs: Organs which are structurally dissimilar but functionally similar.

· Vestigial Organs: Function less, organs whose presence is not required.

iii) Embryological evidences :

· Embryological evidences show that different vertebrates have similar developmental pattern.

· This suggests the common origin and the same ancestral stock.

iv) Molecular evidences :

Molecular evidences are seen in the form of similar cell organelles, proteins, gene functioning catabolic activities, ATP as energy currency, etc.

17. Geological time Scale:

Geological time is arrangement operas, periods and epochs, the time scale in an order of their age.

i) Eras: Azoic, Archeozoic, proterozoic, palaeozoic, Mesozoic and Coenozoic.

ii) Periods :

· Periods of Paleozoic era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian.

· Periods of Mesozoic era: Triassic, Jurassic, Cretaceous.

· Periods of Cenozoic era: Tertiary and Quaternary.

iii) Epoch: Holocene, Pleistocene, Pliocene, Miocene, Oligocene, Eocene, Paleocene.

18. Adaptive radiation:

Transformation of original species to many different varieties in order to adapt their surroundings is called adaptive radiation.

19. Dardy-Weinberg Principle :

Hardy-Weinberg principle states that the gene frequencies remain the same form generation to generation unless disturbed by factors like mutation, nonrandom and genetic drift, etc. There is no evolution, if Hardy Weinberg equilibrium is established.

20. Origin and evolution of Human being:

i) Order Primates is divided into two sub-orders-Prosimii (including lemurs, Lories and tarsiers,) and Anthropodea (including new world monkeys-Ceboidea, Old world monkeys-Cercopithecoidea, Apes and Man-Hominoidea.)

ii) Hominoid evolved in Miocene in three separate lines are shown as under:

· Hyalobatidae – Bibbons

· Pongidae – Gorilla, Chimpanzee and Orangutan

· Hominidae – Primates with human characteristics.

21) Suborder of Primates:

i) Prosimii: Lemurs and tarsiers.

ii) Anthropoidea : New world monkeys such as squirrel monkey, spider monkey and old world monkeys such as baboons, macaques, languor’s.

iii) Hominoidea (Hominoids) : Apes and man.

22) Paleontological evidences of human evolution:

The available fossils are skills,, mandibles, teeth, bones like humerus, femur and stone implements.

23) Four main stages in the origin of man:

i) Ape-stage: Propliopithecus.

ii) Ape-men stage: Ramapithecus, Kenyapithecus and Australopithecus.

iii) Primitive men (Prehistoric man) :

· Homo habilis (Handy man).

· Homo erectus (Java man and Peking Man)

· Homo heidelbergensis (Heidelberg man)

· Homo neanderthalensis (Neanderthal man).

iv) Modern men :

· Cro-Magnon man (Homo sapiens fossils)

· Homo sapiens sapiens.

The Fascinating Science of Origin and Evolution of Life