Origin of Life – Geography – UGC NET – Notes

Evolution

Evolution mainly deals with the origin of life on earth. The conditions and the forms of life on earth were entirely different from what we see today. Everything evolved from one form to another for a better chance of survival.

The Origin of the Universe

The origin of life begins with the origin of the universe. The universe, an old vast and empty space comprising galaxies, originated around 20 billion years ago. There was nothing but blackness filled with gas and dust. The Big Bang Theory is the most accepted theory regarding the origin of the planet earth and the existence of different life forms on it. According to this theory, the universe is a result of a massive explosion which occurred 20 billion years ago. Whether it is a hypothesis or a fact, a new universe was formed. The atmospheric condition after the explosion became more stable. The temperature reduced and gasses like hydrogen and helium formed which led to the formation of galaxies of today.

Later, after 10 billion years, the earth was formed which was covered by water vapour, methane, carbon dioxide, and ammonia. There was no atmosphere but only gases and moisture. The powerful rays of the sun stimulated and hastened evolution. By making and breaking bonds between gas molecules, the earth came out with a new face. After millions of years i.e., once the earth’s atmosphere was stable, the first life on earth came into existence (around 4 million years ago). There began the story of the origin of life on earth.

The Origin of Life

There were lots of hypotheses regarding the origin of life on earth. Certain experts suggested that life came from outer space as spores while another group explained that life came from a non-cellular component such as decaying matters like mud. The latter theory was known as the theory of spontaneous generation, which was discarded later.

In the year 1953, Oparin and Haldane suggested that life originated from non-living organic molecules like proteins and RNA. This was followed by the theory of chemical evolution which suggested that atmospheric conditions of the earth led to the formation of organic molecules from inorganic molecules. Few scientists conducted experiments regarding the same. However, once the first life came into existence, they started to evolve in different ways and forms. This laid a stepping stone to the theory of evolution.

Theory of Special Creation

The greatest supporter of this theory was Father Suarez. According to this theory life was created by supernatural power. 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. According to Hindu mythology the world was created by God Brahma. Brahma is considered the God of creation.

He created the whole universe with his desire. The first man was Manu and the first woman was Shradha. Special creation theory lacks scientific evidences, on account of which it is not accepted.

Theory of Spontaneous Generation (Abiogenesis or Autogenesis)

This theory states that life originated from 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. These beliefs have no scientific grounds and hence are discarded.

Evidences against the Theory of Spontaneous Generation:

The theory of spontaneous generation was disproved by many scientists of 17th, 18th and 19th centuries. They proved that new organisms can be formed from pre-existing ones, i.e., omnis vivum ex ovo or vivo (‘Biogenesis’ of Harvey-1651 and T. H. Huxley-1870). Noted scientists who experimentally challenged the theory were Francesco Redi (1626-1697), Lazzaro Spallanzani (1729-1799) and Louis Pasteur (1822-1895).

(i) Redi’s Experiment:

Francesco Redi, an Italian physician, took the flesh and cooked it so that no organisms were left alive. Then he placed flesh in three jars, of which, one was uncovered, the second was covered with parchment and the third one was covered with fine muslin. He kept these jars for a few days and observed that maggots developed only in the uncovered jar though the flies also visited other jars.

(ii) Spallanzani’s Experiment:

Spallanzani (1765), an Italian scientist disproved the spontaneous generation of microorganisms. He experimented that animal and vegetable broths boiled for several hours and soon after sealed, were never infested with microorganisms. From this experiment he concluded that high temperature had killed all living organisms in the broths and without them life could not appear. When the broths were left exposed to air, were soon invaded by microorganisms.

(iii) Pasteur’s Experiment:

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.

But according to biogenesis, life originated from pre-existing life which does not explain the origin of life. So / к biogenesis is also disapproved.

Theory of Panspermia or Cosmozoic Theory or Spore broth Theory

This theory was proposed by Richter (1865). According to this theory, ‘protoplasm’ reached 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. In fact, panspermia theory is the alternative name of cosmozoic theory.

Evidences against Cosmozoic Theory:

Living matter cannot survive the extreme cold, dryness and ultra-violet radiation from the sun required to be crossed for reaching the earth.

Theory of Eternity of Life

This theory was proposed by Preyer in 1880. According to this theory, different types of living beings have always existed on earth and shall continue to exist forever, changing only in form.

Evidence against Theory of Eternity of Life:

It is accepted that earth had not always existed. If life is eternal, where did it exist before this planet was formed.

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.

Theories of Inheritance of Acquired Character

Lamarck’s Theory of Evolution

Lamarckism is the first theory of evolution, which was proposed by Jean Baptiste de Lamarck (1744-1829), a French biologist. Although the outline of the theory was brought to notice in 1801, but his famous book “Philosophic Zoologies” was published in 1809, in which he discussed his theory in detail. Lamarck coined the terms “invertebrates” and “Annelida”. The term “Biology” was given by Lamarck and Treviranus (1802).

Lamarck’s Propositions:

Lamarckism includes four main propositions.

1. Internal Vital Force: All the living things and their component parts are continually increased due to internal vital force. Lamarck.
2. Effect of Environment and New Needs: Environment influences all types of organisms. A change in environment brings about changes in organisms. It gives rise to new needs. New needs or desires produce new structures and change habits of the organisms. Doctrine of desires is called appetency.
3. Use and Disuse of Organs: If an organ is constantly used it would be better developed whereas disuse of organ results in its degeneration.
4. Inheritance of Acquired Characters: Whatever an individual acquires (to possess) characters in its life time due to internal vital force, effect of environment, new needs and use and disuse of organs, they are inherited (transmitted) to the next generations. The process continues. After several generations, the variations are accumulated upto such extent that they give rise to new species.

Examples in Support of Lamarckism:

Lamarck explained his theory by giving the following examples.

1. Evolution of Giraffe: The ancestors of giraffe were bearing a small neck and forelimbs and were like horses. But as they were living in places with no surface vegetation, they had to stretch their neck and fore-limbs to take the leaves for food, which resulted in the slight elongation of these parts. Whatever they acquired in one generation was transmitted to the next generation with the result that a race of long necked and long fore-limbed animals was developed.
2. Webbed Toes of Aquatic Birds: Aquatic birds like ducks have been evolved from the terrestrial ancestors.
3. Disappearance of Limbs in Snakes: The snakes have been evolved from lizard like ancestors which were having two pairs of limbs.
4. Flat Fishes: They are flat and bear both the eyes on one side and live at the bottom of the water. During the embryonic stage their eyes are present laterally, one eye on either side. The body of these fishes is not flat at this stage but later on both the eyes is shifted to one side and the body becomes flat to withstand the pressure of water.
5. Flightless Birds: The ancestors of these birds (e.g., Ostrich) were capable of flying, but due to some environmental factors they had plenty of food and were well protected. So they did not use their wings and that is why the latter became vestigial.
6. Retractile Claws of Carnivorous Mammals: The ancestors of carnivorous mammals such as lions, tiger etc. had ordinary claws for tearing the flesh of their preys. As the latter gained in running, the carnivorous mammals also had to run fast for which claws were a hindrance. The animals, therefore, developed retractile claws. TOR
7. Deer: The ancestors of deer were not having so much speed in running, but as they needed protection from other animals of that time they started running, due to which present speed were achieved by the deer.
8. Cave Dwellers: The ancestors of cave dwellers had normal eye sight. On account of living under continuous dark conditions, the animal lost their power to see.
9. Emergent Hydrophytes: The effect of environment and inheritance of acquired characters is clearly seen in emergent hydrophytes like Ranunculus aquatilis. Here the submerged leaves are dissected while the emerged ones are simply lobed. When the plant is grown out of water, all the leaves are un-dissected. In the submerged environment all the leaves are dissected.

Criticism of Lamarckism:

• The first proposition of Lamarck suggests the tendency to increase in size. While the evolutionary trend in certain groups of organisms may be associated with the increase in size, there are many cases, where evolution proceeded not only without any increase in size but rather through a reduction in size. Many plants contradicts this principle by showing such a reduction in size during their evolution.
• The second Lamarckian principle that new organs result from new needs, is quite manifestly false. In the case of animals, he believed that the environment acted through the nervous systems; in other words, the desire of the animal leads to the formation of new structures. In its crudest form this would mean that the man who mused “Birds can fly, so why can’t I?” should have sprouted wings and taken to the air.
• The third Lamarckian principle that organs will develop due to use and degenerate due to disuse may be correct as far as growth of an organ within the lifetime of an individual is concerned. However, this principle is meaningful only when it is studied in relation to the following fourth principle.
• The fourth proposition of Lamarck was that the inheritance of characters was acquired during the life time of the individual. This principle has been experimentally found incorrect. Certain experiments which have discredited it are the following:
  • August Wiesmann was the first person to make a definite distinction between heritable changes and those which cannot be inherited. According to Wiesmann, the characters influencing the germ cells are only inherited. There is a continuity of germplasm but the somatoplasm (protoplasm of somatic cells) is not transmitted to the next generation hence it does not carry characters to next generation. Weismann cut off the tails of rats for more than 20 generations and allowed them to breed, but tailless rats were never born.
  • Loeb artificially fertilized the eggs of sea urchin by certain chemical stimuli and these parthenogenetically fertilized eggs produced the generations, the members of which possessed no parthenogenesis.
  • Boring of ears and nostrils in Indian women is never inherited to the next generations. All the aforesaid cases and experiments clearly showed that Lamarckian theory is not tenable.