Evolution and opinion of biologist.....part2

Formation of theory of natural selection.

Darwins frame an outline of theory of natural selection,which was elaborated in 1844 in the form of a long essay but was not published.

Malthus 1766-1913 published essay on the principle of population.Alfred Russell wallace 1823-1913 another naturalist working in East indies developed a theory of natural selection identical to Darwins.

The theory was presented to the Linnaen society of london on 1st july,1858 under joint authorship of Darwins and wallace.

Over a year later,in November 1859,Darwins published the theory by his own name in the form of a book "On the origin of species by means of natural selection".In this book Darwins develop two main points.

1.Descent with modifications:

According to Darwin organism surviving today are descendants of some common ancestors that lived in remote past.

In the Darwins view,the history of life like a tree,with multiple branching and rebranchanging from a common trunk all the way to the tips of living twigs,symbolic of the current diversity of organisms.

At the each fork the evolutionary tree is an ancestors common to all lines of evolution branching from the fork.

2.Natural selection and adaptation:

Darwin suggest that population of individuals species become better adapted to their local environment through natural selection.

Based....

Production of more individuals than the environment can support,leading to struggle for existence.

Survival in the struggle for existence is not random.Those individuals whose inherited characters fit them best in the environment are likely to leave more offspring than less fit individuals.

This leads to gradual changes in population which accumulate over the generation,thus leading to evolution of new species.

Steps/points of Darwins theory:

1.variation

2.over-population

3.survival of the fittest

4.struggle of the fittest

5.Origin by species by mean of natural selection

1.Variation:

The individual of every species show many differences.

No two individuals are ever exactly alike.

Although Darwins did not know the nature of this variability yet he knows the most of that most of these variation were hereditary.

2.Over-population:

The population size of all organisms rapidly increases by reproduction in the other words there is an overproduction all over all the organisms produce offspring in far greater number than can possibly survive.

3.Survival of the fittest:

In this competition the individual with more useful variation or more fit are better adapted to their environment and hence remain alive in the struggle for existence.

In other words nature select such organisms for survival and future reproduction and weeds out the order.

4.Struggle for existence:

Over production naturally leads to a serve competition among the individual of a population for necessities of life .

5.Evolution of new species:

The operation of natural selection generations after generations leads to accumulate of more and more favorable variation in the succeeding generation.

Neo-Darwinism:

The theory of evolution proposed by Darwin has been modified in the light of population genetics.

Variation within population

the quantative characters therein.

With the progress in population genetic 1930,Mendelism...

Darwinism were reconclines and the genetic basis of variation and natural selection was worked out.

An extensive theory of evolution was thus developed in 1940.

It is also called synthesis because it includes discoveries and ideas fromay different field of biology including paleontology taxanomy biogeography ecolgy ethology and the population genetics.

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