Due to the variations some individuals would be better adjusted towards the surroundings than the others.Īdaptive modifications are caused through the struggle for existence. It means there are differences among the individuals. Thus, climate and other natural factors also help in restricting the number of individuals of particular species.Įxcept the identical twins, no two individuals are similar and their requirements are also not exactly the same. It is the struggle between the organisms and the environmental factors, such as drought, heavy rains, extreme heat or cold, earthquakes, diseases, etc. For example, a fox hunts out a rabbit, while the fox is preyed upon by a tiger. This struggle is normally for food and shelter. It is the struggle between the members of different species. The thinking of both Darwin and Wallace in respect of organic evolution was similar. The essay was titled “On the Tendencies of varieties to Depart Indefinitely from the original type”. Alfred Wallace (1823-1913), a naturalist from Dutch East Indies was working on Malay Archipelago (present Indonesia). While Darwin was busy in formulating his theory of natural selection, he received a brief essay from Alfred Wallace in June 1858. have also been produced through selective breeding. Many crop plants like broccoli, cabbage, cauliflower (Fig. He also observed that humans have perfected the toy-like Shetland pony, the Great Dane dog, the sleek Arabian race horse and many cultivated crops and ornamental plants. The breeders have successfully produced cows that give increased amount of milk. Thus Darwin was much influenced by Malthus Theory of human population growth.ĭarwin came to know that humans have been modifying wild plants and animals to suit their requirements. Darwin considered that like in humans, competition exists among all living things. Darwin noticed the conflict between resources of population and its continued reproductive pressure.
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