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9TH CLASS BIOLOGY Classification- వర్గీకరణ


                                9TH CLASS BIOLOGY CLASSIFICATION Charles Darwin developed the idea that each species had developed from ancestors with similar features, and in 1838, he described how a process he called natural selection would make this happen.Darwin's idea of how evolution works relied on the following observations:
1. If all the individuals of a species reproduced successfully, the population of that species would increase uncontrollably.
2. Populations tend to remain about the same size from year to year.
3. Environmental resources are limited.
4. No two individuals in a given species are exactly alike.
5. Much of this variation in a population can be passed on to offspring.
Darwin deduced that since organisms produce more offspring than their environment could possibly support, there must be a competitive struggle for survival - only a few individuals can survive out of each generation. Darwin realized that it was not chance alone that determined survival. Instead, survival depends on the traits of each individual and if these traits aid or hinder survival and reproduction. Well-adapted, or "fit", individuals are likely to leave more offspring than their less well-adapted competitors. Darwin realized that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population. Traits that help an organism survive and reproduce would accumulate over generations. On the other hand, traits that hinder survival and reproduction would disappear. Darwin used the term "natural selection" to describe this process.
Observations of variations in animals and plants formed the basis of the theory of natural selection. For example, Darwin observed that orchids and insects have a close relationship that allows the pollination of the plants. He noted that orchids have a variety of structures that attract insects - so that pollen from the flowers gets stuck to the insects’ bodies. In this way, insects transport the pollen from a male to a female orchid. In spite of the elaborate appearance of orchids, these specialized parts are made from the same basic structures that make up other flowers. Darwin proposed that the orchid flowers did not represent the work of an ideal engineer, but were adapted from pre-existing parts, through natural selection.
Darwin was still researching and experimenting with his ideas on natural selection when he received a letter from Alfred Wallace describing a theory very similar to his own. This led to an immediate joint publication of both theories. Both Wallace and Darwin saw the history of life like a family tree, with each fork in the tree’s limbs being a common ancestor. The tips of the limbs represented modern species and the branches represented the common ancestors that are shared amongst many different species. To explain these relationships, Darwin said that all living things were related, and this meant that all life must be descended from a few forms, or even from a single common ancestor. He called this process "descent with modification".
Darwin published his theory of evolution by natural selection in On the Origin of Species in 1859. His theory means that all life, including humanity, is a product of continuing natural processes. The implication that all life on earth has a common ancestor has met with objections from some religious groups who believe even today that the different types of life are due to special creation.Their objections are in contrast to the level of support for the theory by more than 99 percent of those within the scientific community today.

                                       

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