![]() ![]() Nature selects only those organisms which are capable of adapting to the changing situations while the rest which are incapable to do so perish away. He also said that, nature also plays an important role in the selection of the fittest. The chances of survival are higher for organisms which show modifications which will help them to survive. He stated that there is a continuous competition between organisms for survival and the strongest of all survives. In this book he explained the theory of natural selection which talks about the survival of the fittest. Darwin’s theory of natural selection: Darwin is famous for the theory which he published in the book titled ‘Origin of Species’. These characters are termed as acquired characters which are transferred from one generation to another.ī. For example: giraffe has a long neck because it used to browse on leaves of tall plants by extending their neck for several generations, shoulders of iron smith are strong due to repetitive hammering movements, wings of ostrich and emu are weak because they are not used for flying, legs of birds and swan are used for swimming because they live in water. He proposed that the reason behind evolution was the changes in the morphological activities of the organism. Lamarckism: Lamarck gave the principle of 'use or disuse of organs’. This similarity in the development of embryos represents common origin of organisms.Ī. Therefore, they inform us about the time when a particular life form existed.ĭ. Fetal science or embryology is used as an evidence of evolution. Comparative study of embryos in vertebrates/chordates shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually. (iii) The most recent fossil is found in a rock nearest to earth’s surface. (ii) They inform us about the extent to which living things have changed over time. (i) They inform us about the types of living things that existed in the past. It has the same shape as the bone, but it is chemically more like a rock.â For example, the fossil of a bone will not have some constituents of the bone in it. The colour of a fossil depends upon the type of minerals that form it. Fossils have the same shape as that of the original animal, but their colour and texture may vary widely. They represent the ancestors of plants and animals, which are alive even today. Fossils provide evidences of evolution by revealing the characteristics of the past organisms, and the changes that have occurred in these organisms to give rise to a present organism. Therefore, this results in the formation of a new species of green beetles, which are reproductively isolated.Ĭ. âℿossils are the remains of organisms that once existed on Earth. For example, the green female beetles of an area will prefer to reproduce with the green males only because green beetles have the survival advantage. These sub-populations will eventually be incapable of reproducing with each other. Thus, the two populations of beetles become completely different from each other. This will result in changes in subsequent generations. For example, a particular sub-population of beetles evolves to blue or green colour due to natural selection or genetic drift. Genetic drift and natural selection: Genetic drift and natural selection can give rise to different changes in sub-populations. ![]() Now, if a river starts flowing between the two populations, then the two sub-populations would be further isolated and the chances of gene flow or reproduction further decreases. ![]() Reproduction will only occur within a sub-population, which will lead to the production of a new species. Geographical isolation: Since this population of beetles is spread over a large area, reproduction cannot occur between individuals of sub-populations. These sub-populations can lead to the formation of an entirely new species. ![]() As a result, sub-populations of beetles are spread over that area. Beetles are small insects, which cannot travel to far off places. Hence, the population of beetles in that area is very large. These two separate populations of beetles are spread on a wide mountain range since their food is widely distributed. Let us consider that a population of beetles has split into two separate populations, which cannot reproduce with each other. In order to understand speciation, let us consider the example of beetles. Speciation may be defined as an evolutionary process, which involves the formation of one or more species from an existing species. ![]()
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