Evolution, Darwin's theory of natural selection.

Evolution, Darwin's theory of natural selection.

First we discuss Evolution. 

EVOLUTION

    A gradual change in characters of population over the course of generation through a long time is called evolution. Variation in plants and animals of today has descended from simpler forms into advance form by the process of evolution. The evolution process is a slow process and can be observed in a population after a long time and not in an individual.

    Biological evolution occurs:

1. Alteration in genetic traits over a long time.

2. Creation of new type of organism from a single type.

     But according to the "theory of special creation" all living organisms had been created by Allah in their current form.

DARWIN'S THEORY OF NATURAL SELECTION

Darwin's theory of natural selection:

Historical background:

     Charles Darwin (1809-1892) was born on February 12, 1809 in England. He was a naturalist. He spent most of his time in collecting and studying thousands of animals and plants. Darwin visit Galapagos island by a ship and spend 5 weeks their. He was surprised to see the diversity of finches and some reptiles in their island. Finally Darwin published his book on.

      "The origin of species by mean of natural selection"

        In this book he discussed his theory about natural selection.

      Charles Darwin observed the variations in beaks of finches. Each type of beak is best suited for a particular task. Some beaks are best for cracking hard nuts, Some for eating small seeds.

      According to Darwin's theory of natural selection, if all the individuals have the same gene, their offsprings will have the same gene. All will have equal chances of survival. Actually it is not so, no evolution without genetic variation. All the individuals of a species are different in characters from each other. There is a natural selection n the members of a population. Members having better adaptation are favoured by nature to survive and reproduce and become more common in the next generation.

       Evolution may occur in the following way:

1. Overproduction:

       Each population of organisms has the capability to reproduce large numbers of offsprings. But the resources in environment are limited. This creates a competition for the survival.

2. Competition:

       There is competition among organisms for survival. The fit organisms can utilize the resources and can survive.

Variations:

       There are genetic variations among individuals of a population. Only those individuals will survive who possess the characters best suitable to the environment. The weak organism will be excluded from the environment.

Natural selection: 

      Nature selects those organisms that have the capability of adaptation with changing environment. It is known as natural selection. The individuals with favourable variations become a major part of population.

3. Reproduction:

       The best adapted organisms can survive and reproduce. They pass on their best variations to their offsprings.

4. Speciation:

       As time and generations continue, adaptations are passed on generation after generation. After many generations and through natural selection new species may evolve from a common ancestor. The favourable changes in successive generations are combined in descendants, which are quite different from their ancestors. It is called speciation.

Artificial selection:

      Selective breeding between individuals of certain quality and traits is called artificial selection. Selective breeding has brought a revolution in agricultural and livestock production throughout the world. Organisms with desirable qualities are selected for breading.

     The artificial breed of animals is known as 'Breeds' while breeding plants are called varieties or cultivars. Numerous breeds of sheep, goat, cow, hen etc. have been produced by artificial selection to increase production of milk, meat, milk, wool and eggs.

     Humans can also bring changes in organisms, for selecting certain varieties for breeding. The expert chooses that animals among the group of animals that have specific characteristics. He allows these animals to breed.

     Similarly many plant varieties have been produced for better quantity and quality of fruits, vegetables and cereals.

Example:

● The major cereals like wheat, rice, maize etc were developed from wild grasses by artificial selection. Cattle breeds are also an  example of artificial selection.

● Different  varieties of animals like cattle, dogs, cats, rabbits and horses are the example of artificial selection.

● Many ornamental plants are the result of selection for attractive features.

Relation b/w Natural selection and survival of the fittest:

Natural Selection:

      Those organisms that have the capability of adaptation with changing environment will survive. It is called natural selection.

Survival of the fittest:

      Those individual will survive l who passes character best suitable to the environment.

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