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CBSE - X - Biology - Heredity and Evolution


Asked by sweetynam 18th February 2009, 4:13 PM
Answered by Expert


Evolution literally means an unfolding. It refers to the gradual and continuous process by which the first and most primitive of living organisms have developed into the more advanced forms of today.


Darwin's Theory of Evolution is the widely held notion that all life is related and has descended from a common ancestor. Darwin's general theory stresses a purely naturalistic (undirected) "descent with modification". That is, complex creatures evolve from more simplistic ancestors naturally over time. In a nutshell, as random genetic mutations occur within an organism's genetic code, the beneficial mutations are preserved because they aid survival -- a process known as "natural selection." These beneficial mutations are passed on to the next generation. Over time, beneficial mutations accumulate and the result is an entirely different organism (not just a variation of the original, but an entirely different creature).


Objections to this theory:

i) Natural selection may be one of the main causes, but not the exclusive cause of structural modifications.

ii) It explains the survival of the fittest but not its arrival or cause.

iii) Only complete variations are useful in the struggle for existence but not those which are still to complete or just born.

iv) If nature selects the suitable forms and features, the theory is unable to explain the lingering existence of the vestigial organs.

v) It has been calculated that the time required by the slow process of natural selection to evolve the present day complex species, is much more than the age of the earth itself.

Answered by Expert 18th February 2009, 5:30 PM

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