Biology-Today.com

1. What are the propositions of Darwin’s theory?

Ans. According to the book “Origin of Species by means of Natural Selection” (1859) the Propositions of Darwin concept may be summarized as follows:

a) Hypothesis:

i) Prodigality of Production.

ii) Resources are constant.

Deductions:

Struggle for existence.

b) Hypothesis:

i) Struggle for existence.

ii) Universal occurrence of variations.

Deductions

Survival of the fittest or Natural Selection.

c) Hypothesis

i) Gradual accumulation and inheritance of advantageous variations.

ii) Action of Natural Selection.

Deductions:

Origin of species.

2. What do you mean by Natural Selection?

Ans. Differential reproduction or survival of replicating organisms are directed by non-human agencies. Since such differential selective effects often act on genetic variations, Natural Selection is a common major cause for a change in the gene frequencies of a population that lead to a new distinctive genetic constitution (Evolution).

3. Who proposed the term of Natural Selection? What is the main proposition of the theory?

Ans. The theory of Natural selection was proposed by Charles Darwin (1809-1882). The main proposition of this theory is: The number of births of organisms always exceeds the corresponding resource content. This leads to a constant struggle for existence among themselves. The organisms having better adaptive ability to cope with their environment get the favour of selection to survive. These selective attributes (adaptive features) get accumulated through generations to give rise new species.

4. What is “Struggle for Existence”?

Ans. The struggle for existence refers to the competition among the individuals for the limited resources of the environment. The competition is a test to the variations in the traits of the organisms. Some of those traits which are useful to the organisms in a given environment are deemed to be adaptations.

5. What are the main points of criticism to Darwinism?

Ans. Darwinism has faced some criticism on some of the important aspects, such as:

a. He laid special emphasis on variations but failed to explain the origin of life.

b. The theory fails to explain the consequences of use and disuse as well as, the presence of vestigial organs.

c. As he could not distinguish the genetic and somatic variations, he thought all the variations as inheritable.

d. He talked about the survival of the fittest, but failed to explain the origin of the fittest.

6. What is Neo-Darwinism? What is its main proposition?

Ans. The drawbacks of Darwin concept have forced his strong supporters, like, Weismann and his followers to reestablish his theory in the light of new findings. This renewed version of Darwinism concept is known as Neo-Darwinism. Its main proposition is Adaptation (or evolution) of organisms is possibly by the action of several factors and Natural Selection is one of such factors.

7. What is ‘Modern Synthesis”?

Ans. The modern synthetic theory of evolution developed between 1930-1940 brought out the importance of natural selection based on the contributions of genetics, systematics and palaeontology. It has clearly been shown that genes regulate the phenotypic effects and all the variation have a genetic basis. It is also clear  that fossil data are fully consistent with Darwinian Theory. Thus Modern Synthesis is reestablishment of Darwinism in light of modern findings.

8. What is Modern Synthetic Theory? What is its main proposition?

Ans. Modern Synthetic Theory is new concept of Evolution developed from the knowledge of Mendelism, Mutation Theory and knowledge of genes. Its main proposition is:

a. Evolution is due to genetic variations caused by random mutation. Recombination may also bring about variations.

b. Reproductive isolation prevents the exchange of genes between different populations to establish the variants.

c. Natural Selection directs the course of evolution.

d. Change in the gene frequency indicates evolution.

9. What is Stabilizing Selection?

Ans. It is the selection that favours the survival of organisms in a population that are at an intermediate phenotypic value for a particular character and eliminates extreme Phenotypes (also called Normalizing or Centripetal Selection). Such selection is characteristic to stable environment and involves no variation.

10. What do you mean by Disruptive Selection?

Ans.  It is the selection that tends to favour the survival of organisms in a population that are at opposite phenotype extremes for a particular character and eliminates individuals with intermediate values (also called Centrifugal Selection).

Such selection results in the formation of sub-populations with different genetic constitution.

11. What is Directional Selection?

Ans. Directional Selection is the selection that causes the phenotype of a character to shift towards one of its phenotypic extremes. Such selection is characteristic to the environment which tends to change continually toward a definite direction leading to new adaptations, e.g., Selection in the evolution of horse.

12. What is Social Darwinism?

Ans.  It is the concept that social and cultural differnces in human societies arise through processes of natural selection similar to those that account for biological differences among populations and spices.

13. What is Darwinian Fitness?

Ans. Darwinian Fitness is the ability of genotype to transmit its genes to the next fertile generation, relative to that of other genotypes in the same environment. Such different genotypes may result in the population through mutation or recombination.

14. What is “Mutation Theory”? What are its main features?

Ans. Mutation Theory is the concept put forwarded by De Vries (1901-1903) which states that “New species originates as a result of discontinuous variations which appear suddenly and full fledged and form the new species at once”. Its main features are:

a) Mutations randomly appear in natural organism groups.

b) Mutation appear suddenly and bring about large changes among them.

c) They are inherited through generations to give rise new species.

d) They arrive in totality at once and there is no intermediate step.

Related Posts

• What is Genetic Drift? (0)
  In many small populations completely random fluctuations in the frequencies of certain alleles or ge...