Resumo de On The Origin Of Species

The animals have been classified into groups in accordance with their likeness to one another since eighteenth century. The species, most of these groups, can produce themselves but never breed with another species. How does the enormous number of Animal species with their varied patterns survive? "What is their origin?? In domesticated animals and plants the variance becomes noticeable in their structure and hence these should be studied as follows:-
1a) the outside factors such as cold, heat, food supply, resistance and;
1b) their inherent factors affecting specially their reproductive organs.

The inheritance factor is essential for the development of characteristic. The variations do not happen in isolation rather in combination with other abnormalities. For example white blue eyed cats are always deaf due to lack of pigments. Over generations an animal body structure also alters depending on the use or disuse of the parts. A domesticated cow?s udders are more developed than the wild ones not milked.

Intercrossing of different breeds should be done by man with care and skill to avoid birth of mixed group of mongrels of different color and sizes. Domesticated plants and animals produce rich varied harvest. (Example: GM /BT crop of plantation or cultivation) Here MAN takes the place of Nature.

The indefinable group of species collectively forms a genus which turns into a family, then the group turns into order and finally into classes. The classes are finally included in ?Phylum? which is the basic pattern developed by the Nature. For example vertebrates or back-boned animals are opposed to arthropods or crustaceans like lobsters, built on different plan.

The individual differences are so remarkable that naturalists frequently confuse about two related animal forms as to whether it is species or a variety of it. The species, varieties and sub species inter mingle into each other so much that they become indistinguishable. The individual differences over generations lead to new varieties which may develop into new species. A small variance in forms and inability to reproduce suggests they are species. The division of life into groups subordinate to groups is due to genus.
A sterile animal despite its strength will be wiped out and so reproducing of its kind is also a part of the struggle for existence. Similarly destruction of individuals and their groups is also important for the survival in order to keep the number of any species down.

As a man selects and rejects according to his needs and usefulness Nature also adopts the same process in more cruel fashion by bestowing its blessing on certain verities and weeding out others. But it does so for the benefit of plant and animal. Nature takes its own time to do its finer and marvelous handiwork. The life span of plant and animal solely depends on the circumstances it has lived or lives in.

Natural selection is a surgeon?s knife by which varieties persisting and reproducing survive and others vanish. It preserves only useful variation. It is concerned with the perfection of an organ from a utilitarian point of view and not as a beauty as admired by human eyes. As the laws of Natural selection concern to the bodily structure and instincts of the animal, the changes take place gradually .An instinct fades away if not used.

Analogous-: The theory of descent with modification states that there may be affinity of animal types due to their common ancestors with modification as animals may resemble each other owing to the acquisition of similar mechanissms under similar circumstances known as Analogical. For example dugongs and whales have similar shapes but the former is a fish and the latter is a mammal.

Homologous-: There is group/class of animals which have resemblance of fundamental pattern in their structure and are known as homologous.

Embryology-: Throws light on the natural affinity of animals. Body?s parts very similar in embryo become completely different with the progress of development. The insects who do not go through the stages of metamorphosis and adopt adulthood pattern early loose the power to learn and make further modification..

Irrespective of the final different adult form similarity of embryo indicates common ancestry. But at the same time dissimilarity does not mean absence of relation of descent as in one group the development may have been suppressed and in the other modified and lengthened not even recognizable.

Rudimentary organ relate to the organs useless and vary widely in size, shape and position in different individuals and are larger in the embryo than in the adult. Disuse may result in the sinking of organs but inheritance continues for generations until it is completely obliterated. In other words Natural selection was the main but not the sole means of modification. By analogy all plants and animal life come from one basic form. The action of poisons, the existence of sex and of forms intermediate between animal and plants life strongly suggest a primitive forerunner of these two living kingdoms.

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