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Interpret Lamarkism & Darwinism.

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Lamarkism :

(A) General 

• Jean Baptist Lamarck was a naturalist of France.

He was professor of Botany in Paris. In 1801 & 1802. he published two papers regarding evolution-

1. Systeme des animare sans vertebras 

2. Researches rural organization des corps vivans.

• In 1809 he described for the first time, the principles of evolution in a book “Philosophic Zoologique”. 

• He coined the term ‘‘Biology”. 

• He for the first time used the terms Invertebrate & Vertebrate. 

• Lamaskism is also called as “Inheritance of Acquired Characters”. 

(B) Assumption of Lamarkism 

• Lamark put forwarded four hypothesis which are collectively called as Lamarkism – 

1. Effect of the environment 

According to Lamark, the environment affect the morphology of the animals which causes changes in the behavior of the animals. As a result some organs or structure of the animals become abnormally active. 

2. Effect of needs 

According to it as a result of change in the requirement some new organ develops in the body of the animals or the structure of the existing organ is modified. 

3. Effect of use and disuse of organs 

According to it. if the organs are used frequently and continuously, they are strengthened, developed and enlarged. On the other hand if not used, they get weaken and finally disappear. 

4. Inheritance of acquired character

According to it the favorable characters which are gained or acquired during the life time of an individual are transmitted to the offspring. The cumulative effect of such acquired characters resulted in the origin of new species. 

(C) Examples of Lamarckism 

1. The ancestors of the modern horse were plantigrade, graminivorous & were living on moist soil. Changes in the environment & habitat caused changes in their habits. Now, they had to feed hard & dry grass and they had to run fast for protection on dry & hard land. Therefore, in due course of time, their legs become long, their cheek teeth get changed, number of fingers is reduced & they became unguligrade. 

2. The long necked giraffes evolved from ancestors having short height & short neck and were feeding grass. As a result of environmental changes, the grass vegetation is lost & the number of trees is reduced. The continuous stretching of neck & fore limbs by their ancestors to catch (feed) high located leaves of the desert plants caused elongation of the neck and the fore limbs have become longer than the hind legs. 

3. Ducks & other swimming birds acquired webbed feet, because the skin between the toes is subjected to stretching due to constant swimming. 

4. Wadding birds acquired long neck & legs from stretching. 

5. In snakes the stretching of the body of their ancestors, as they made their way through narrow passages in thick vegetation, lead to their elongation. The disuse of the limbs in such environment caused their gradual reduction & final disappearance. 

(D) Criticism of Lamarckism 

Lamarckism was criticized by many scientists. Cuvier and Weismann were the main opponent of the Lamarckism. 

Weismann (1885) proposed germplasm theory and contended that acquired characters are somatic & could not be transmitted. Weismann did one experiment on white rats by cutting their tails. He could not find reduction in the size of tail even after 22nd generation. 

Lamarkism is unable to explain follows points

1. Chinese females wear iron shoes so as to reduces the size of the feet. But children are born with normal feet even after several decades. 

2. The muscles of athletes are never inherited to their offspring. 

3. Piercing of ears & nose in India has been a tradition since decades but never a child is born with pierced nose & ears. 

4. Callosities on palm of blacksmith, farmers & labors etc. are never transmitted to their offspring. 

(E) Neo-Lamarckism 

Recently faith in the Lamarckism has been revived. Many scientists such as Sumner, Me Dougall, Tover, Pavlov, Lindsey Kammerer etc modified the Lamarckism and named its as Non-Lamarckism. These scientists proved by experiments that some of the acquired characters are inheritable. Such as

1. F.B. Sumner in an experiment on white rat had observed that when the rats are reared at 20 to 30 C the body, tail, pinnae & hind legs get longer. These characters were found to be inheritable. 

2. Me Dougall performed an experiment on rats. He trained the rats to escape from water tank through the zigzag path up to 45 generations. He observed that the rats committed less mistakes during training from generation to generation. 

3. Tover performed experiment on potato beetles. He observed that the beetles develop some somatic changes when the embryonic stages of battle are kept in extreme conditions of temperature & moisture. The changes were found to be inheritable. 

4. Pavlov in an experiment trained the doges to come for food in responses to a sound of bell. He observed that less training was required from generation to generation.

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Darwinism :

(A) General 

Charls Darwin (1809 to 1882) was an English naturalist. He made world tour on a British fighter ship, “Beagle”. He collected various animals from different islands & countries. He studied Finches birds on Galopagos island of South America. These birds are now called as Darwin,s Finches. 

A. R. Wallace (1823 to 1913) simultaneous to Darwin, but separately published view s similar to the Darwin. In 1858, the views of both Darwin & Wallace were published in a joint paper which were based on the views of Malthus. 

In 1859, Darwin published a book “Origin of species by natural selection. Darwinism is also called as “Theory of natural selection”. 

(B) Six fundamental propositions of Darwinism. 

1. Enormous fertility or over production in organisms. All animals & plants have an tendency of over production. 

Examples – 

A rabbit reproduces 3 to 4 times in a year and each time gives birth to 4 to 6 young ones. An oyster lays about 6 crore eggs in a year. Similarly, an ascaris lays about 2.5 crore eggs in a life spawn. If the entire progeny survives and multiplies, it will be eight times the size of the earth in a year. 

Elephant is a slowest breeder, matures at the age of 30 years. it’s life spawn is of 100 years and a single female gives birth to six young ones in its life spawn. It is calculated that in 750 years a single pair of elephant give rise to 1.9 crore of elephants. Thus all animals multiply in geometrical ratio but still their number is maintained at a constant level. 

2. Struggle for existence 

Irrespective of over production, the animal population is maintained at constant level. Because the food & space are limited which results in struggle for existence. The struggle for existence is of three types- 

(a) Intra specific struggle 

(b) Inter specific struggle 

(c) Extra specific struggle 

The animals which are not successful in the struggle, do not survive. 

3. Variation & Heredity 

Variations occur commonly in the organisms and no two individuals are alike. The fittest which survive have advantageous variations.

Variations give rise to new characters and heredity passes them on to the next generation. 

There are three sets of contrasting variations- 

(a) Meristic and substantive variations 

(b) Continuous and discontinuous variations 

(c) Somatic and blastogenic variations 

4. Survival of the fittest or Natural selection 

In the struggle for existence only for existence only those individuals survive which are fitted biologically to the new conditions, as they possess advantageous variations. The animals which are unfit get perished Darwin called it “Natural selection “ and the Spancer termed it “ survival of fittest”. 

5. Adaptation to the environment

Environment of any region is never constant. The environment changes are in food supply, climatic conditions (temperature, lightning, drought, food) and geographical conditions. The variations which best suited in a given environment may prove unfavorable in the changed environment. Therefore, in order to survive an organism must be capable of changing in response to the changing environment. 

For example in Mesozoic era, the environment was suitable for the dinosaurs, They ruled the Earth & occupied land, water and air. But later on in the Mesozoic are glaciations led to changes in the temperature and the vegetation became rare. In these conditions, the dinosaurs could not cope with the environment & soon became extinct. 

6. Origin of new species 

In the due course of time, the fittest are automatically selected. They survived & adapted to the natural environment. The adaptations of the survivors may result in the formation of new structures which are called as variations. The useful and favorable variations were transmitted from generation to generations and led to the formation of new species.

(C) Criticism of Darwinism 

Initially, Darwinism was accepted enthusiastically, but later several objections were pointed by the scientists which are as follows- 

• It describes the survival of fittest but not the “origin of fittes” 

• It’s natural selection does not explain the presence of the connection links. 

• It’s natural selection fails to explain super specialization of some organ, as a result some species get extincted. 

• Darwin was ignorant about heritable & non-heritable variations. It is called as agnostic period of Darwinism. 

• Darwin described micro variations in the evolution, but he failed to explain the initial origin of an organ. 

• Darwinism failed to explain variations found in somatic & germ cells. 

• Darwinism fails to explain the presence of vestigial organs. 

• Darwinism failed to explain that in man sometimes most unfit but luckiest are protected and the fittest are handicapped. It fails to explain toe origin of terrestrial animals from, the aquatic animals. 

• Darwinism failed to explain that how the characters are acquired & modified. 

(D) Neo-Darwinism 

In the beginning of 20th century, Darwinism had been modified on the basis of modem discoveries which is now called as New-Darwinism. 

Neo-Darwinism was strongly supported by Wallace, Davenport, Waldane etc New-Darwinism includes following 5 series

1. Gene mutation 

2. Changes in the number of structure of chromosomes 

3. Genetic re combinations 

4. Natural selection & 

5. Reproductive isolation 

(1) Gene mutations 

Change in the number of sequence of nucleotides in the DNA of gene is called as gene mutation. 

Most of the mutations are detrimental but few may be beneficial .

The gene mutations are caused due changes in the environment. There is no specific rate of mutations Normally, gene seldomly mutates but the large number of genes & large number of organisms provide sufficient chances of variations. 

(2) Changes in the structure & number of chromosomes 

Changes in the configuration & number of nucleotides & genes led to changes in the structure of the chromosome. These change are caused as a result of delition, duplication, translocation & inversion. 

Changes in the structure of the chromosomes causes variations in the animals which finally led to origin of species. 

(3) Genetic recombination 

Game to genesis involves meiosis in which crossing over results in the development of new genetic re combinations. As a result variation are generated in the organisms. 

(4) Natural selection 

Natural selection facilitates beneficial gene recombination’s to flow into the off springs. 

(5) Reproduction isolation 

When the different populations of a species get isolated by the barriers, after some times they fail to interbreed. It is due to the acclimated changes appeared in the gene structure as a result of mutations, chromosomal aberrations & polyploidy. These changes lead to the variations, as result the populations evolved into a new species. 

Geographical barriers like mountains, sea, rivers etc and physiological barriers prevent intraspecies reproduction 

The species which are developed as a result of geographical barriers are called as allopatric species. The species which are developed as result of reproductive (physiological) isolation in the same geographical environment are called as sympatric species.

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