Biology : Darwin Theory of Evolution (Darwinism)

Darwin Theory Of Evolution (Darwinism):

        Charles Darwin (1809 – 1892) was an Englishman. He was interested in observing the natural environments and collecting specimens. He was appointed to the post of Naturalist on the ship H.M.S Beagle in 1831. This ship was to make a five years (1831 – 1836) cruise around the world to observe and collect specimens of plants and animals from different places. During this trip, Darwin made many observations some of which are as follows:
On Galapagos Islands, which are in the Pacific Ocean, he found huge tortoise. He observed that the tortoise of each island were different from those of the other.
He also found that there were many different species of Birds (Finches) living on these islands. He observed that although the species resembled with those of mainland but the species of various islands differed in the size and shape of their beaks in accordance with their eating habits.
       
        On return from this trip, Darwin read an essay by Thomas Malthus on the principles of Population. In this essay, Malthus wrote that human population increases at a fast rate whereas resources for the food and space are limited. The result is that there is competition among the individuals for food. He has observed that there is tremendous crowding of living thing on Earth. The new individuals which are produced have to compete for food and space which reduced their chances of survival. Darwin had another observation in mind as to how certain desirable features in pigeons and certain plants could be artificially selected by a careful breeding progamme.
        In 1859, Darwin presented his theory in a book “On the Origin of Species by Means of Natural Selection”, in which he discussed the methods of evolution. The main points in Darwin's Theory can be summarized as follows:
Over Production.
Limiting Factors.
Struggle For Existence.
Hereditary Variations.
Natural Selection.

1.  Over Production:
Most species have a tendency to produce for more offspring than needed to maintain the population. If, for example, bacteria keep on reproducing unchecked, this will result in about 2,000 tons of bacteria in 24 hours. Same is the case with other living organisms.
2.   Limiting Factors:
    For each specie there are certain checks or controlling factors which keep the number of individuals in a     limited range. One of the most important to these checks is the limited food supply. Other limiting factors     include predatory animals, diseases and limitation of space for normal growth and reproduction.     Inanimate Environment which may include such factors like climate, seasonal changes and catastrophe     of various kinds, play a significant role in checking the number of individuals of each specie.
3.   Struggle For Existence:
    Since space and food are limited, the offspring in which generation must compete with one another     for obtaining necessities of life. This competition may be among the individuals of the same species     or the individuals of different species. Darwin called this as the Struggle for Existence.
4.   Hereditary Variations:
    In many species, the characters of the individuals are not alike. They may differ in the exact size or shape     of the body parts, in resistance to a particular disease and so on. Not two individuals are alike, not even     the identical twins. Darwin thoughts that some of these variations are passed on to the next generations.     They are called Hereditary Variations and are important in Evolution.
5.   Natural Selection:
    Darwin realized that individuals with variations that make them better adapted to their environment,     survive and reproduce in greater number than those less fit. Thus these favorable variations tend to be     passed on to the next generation. Over many generations favorable variations gradually accumulate in     the species and unfavorable variations disappear. Eventually, the accumulated changes become so great     that the net result is a new specie.

    Let us try to account for the evolution of the modern giraffe with Darwin's Theory. The original giraffe's population had some individuals with short necks and some with long necks. The ones with long necks could eat leaves of the trees as well as grass on the ground. During period of time, the grass was scarce, the giraffe with long neck could obtain more food than others and were more likely to survive and reproduce. This favorable variation of long neck was inherited by the offspring. The modern day, long necked animals in the result of the process of evolution.