Theories of Evolution: Neo-Lamarckism & Darwinism for Competitive Exams

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Image of Neo-Lamarckism

Image of Neo-Lamarckism

Image of Darwinism

Image of Darwinism

Theories Of Evolution: Neo-Lamarckism & Darwinism Modification of species (Anthropology)

  • A group of evolutionary biologists such as McDougall, Spencer, Cope, Packard, Kammerer and Sumner etc., further studied and modified the Lamarckism.

  • Lysenko, a powerful scientist in the uppermost hierarchy of communist Russia in early 1950s, was such a vehement supporter of Lamarckian theory that he put all finances in jeopardy by undertaking large-scale wheat development programmes based on the theory of inheritance of acquired characters only to be discredited and scarified later on:

  • Following are the experiments in support of inheritance of acquired characters are worth mentioning:

  • F.B. Sumner’s Experiment: He reared white rats at 20o C to 30o C and found that rats develop larger bodies, Long tail and hind feet and these acquired characters were transmitted to the next generation. However, high temperature may have effected germ cells along with soma cells.

  • Tower’s Experiment: He kept potatoes in experimental harsh conditions and found altered structures which were transmitted. The experiment suffers with the same flaw as of Sumner’s experiment.

  • Kammerer’s Experiment: Kammerer reared larva of Salamander in yellow & black boxes and tried to show that animal acquires such colourful features and transmit it to the next generation. When Kingsley Nobel, the famous American biologist, visited laboratory of Kammerer, it was found out that he had fraudulently painted the adults with China-ink to prove his point. The disrepute was so overbearing that Kammerer had to commit suicide.

  • Griffith’s Experiment: He put white rats in cage and rotated it on a wheel in such a way that rats developed dizziness. This dizziness was shown to be inherited in various degrees by the offspring. It has not been confirmed by others.

  • McDougall’s Experiment: He trained white rats to come out through maze fitted with electrical wiring so that when a rat committed mistake it got a shock. Such trained rats were mated and later generations were raised which were again put to maze learning experiment. It claimed that number of mistakes committed decreased in succeeding generations indicating inheritance of learning, an acquired character.

DARWINISM

Image of DARWINISM

Image of DARWINISM

  • Charles Robert Darwin (1809-1882) was born on 12th February, 1809 at Shrewsbury in England. As a student, he studied the Greeks and encountered the views of Thales, Empedocles and Aristotle. He also read the view of his grandfather and the comprehensive theory of Lamarck. With this background, it is apparent that Darwin had at least been exposed to much of the past development of evolutionary thought. Darwin was given an opportunity by British government in 1831to travel by HMS Beagle for a voyage of world exploration. He went on the voyage from 1831 to 1833 and explored the fauna and flora of a number of continents and islands of which Galapagos Islands are the most important.

Image of Charles Robert Darwin

Image of Charles Robert Darwin

  • The publication of T.R. Malthus, Sir Charles Lyell and Alfred Russel Wallace influenced Darwin very much.

  • Malthus (1798) published an essay titled “On the Principles of Populations” which states that populations increase geometrically and food sources increase arithmetically.

  • Charles Lyell (1797- 1875) in his book ‘Principles of Geology’ presented the theory of Uniformitarianism. His theory is based on studied of rock layers and geological processes. According to his theory the earth was always shaped and reshaped by geological forms from the beginning acting slowly over long period of time. Fossil materials provide evidence to Lyell’s hypothesis.

  • Darwinism is the term coined for the explanation offered by Charles Darwin for the origin of species by natural selection. Darwinism consists of five principles which are:

Image of Darwinism consists of five principles

Image of Darwinism Consists of Five Principles

  • Over-production or Prodigality of over-production: Many more individuals are born each generation than will be able to survive and reproduce. Though, as a matter of fact not young ones (eggs or babies) survive to reproduce, they can be destroyed at different stages.

    • By predation: Eggs and larvae constitute food for many species of animals and since they defenseless, they fall easy prey.

    • Delicate & low viability: The eggs and larvae are immature stages of organisms, are delicate, tender with low viability and very few reach adulthoods.

    • Low Susceptibility Against Biotic & Abiotic Vicissitudes: Since eggs are delicate and fragile, they are easily parasitized and killed. Besides even normal environmental factors are unbearable to them.

  • Variation and Heredity: There is natural variation among individuals of the same species. (This had been noted by naturalists from Aristotle through Lamarck but Darwin’s own observations made the greatest impression of this fact upon him.) Many of the favorable adaptations are hereditary and are passed on to the progeny of future generations.

  • Survival of the fittest or natural selection: Individuals with certain characteristics have a better chance of surviving and reproducing than others with less favorable ones. (This is the concept of the survival of the fittest through favorable adaptations to the conditions of life.)

  • Struggle for existence: Organic beings increase by a geometrical ratio, while food production only increases in an arithmetic ratio. So that in a very short time, an area will be over populated with any one species, unless something happens to check the increase. As a result, there is a struggle for existence which is three-fold as given below:

Image of struggle for existence which is three-fold

Image of Struggle for Existence Which is Three-Fold

  • Intraspecific Struggle: found among the individuals of same species. The competition is heavy in case of intraspecific struggle, because the needs and requirements of the members of the same species are same who lives in the same environment. It is the most severe check on the rate of reproduction.

  • Interspecific Struggle: found among organisms of different species living together. Members of one species struggle with other species for similar requirements i.e., food, shelter and mating.

  • Struggle with the environment: Living organisms struggle with the adverse environmental conditions like floods, cold waves, heat waves and earth quakes, etc.

Modification of Species in the Long Geological Periods

  • Gradual modification of species could have occurred over the long periods of geological time through additive process occurring in the past in the same manner as they are occurring in the present.

  • Charles Lyell’s geological interpretation provided knowledge of the long span of time necessary for evolution to proceed and supplied Darwin with the concept of uniformitarianism as a modus operandi for the process of biological evolution

#Theories of Evolution: Neo-Lamarckism & Darwinism

# F.B. Sumnner’s Experiment, Tower’s Experiment, Kammerer’s Exp, Griffith’s Exp, McDougall Experiment.

#Darwinism – Introduction of Charles Robert Darwin.

#Malthus- Population’s Theory

#Charles Lyell- Theory of Uniformitarianism.

#5 Principles of Darwinism- Over production, Variation and Heredity, Struggle for existence, Survival of the fittest, Modifications of species.

# Physical Anthropology

#NET

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