Theories Of Evolution

Darwin's theory of natural selection proposes that within any population individuals vary in heritable traits, and those whose variations best suit the environment tend to survive longer and leave more offspring. Over many generations this differential reproductive success gradually changes the population's characteristics, leading to adaptation and eventually the origin of new species. The option of inheritance of acquired characters describes Lamarck's theory, which held that traits gained during an organism's lifetime are passed on; this idea was later discredited. The choice of sudden large mutations alone reflects the mutation theory of de Vries (saltation), which Darwin's gradualism did not emphasise as the sole mechanism. The notion of an internal vital force guiding progress is a vitalistic, non-scientific concept rejected by Darwinian thinking. As explained in NCERT Class 12, Chapter 7 (Evolution), natural selection works on existing variation, favouring the fittest. As a consistency check, since only heritable advantageous traits increase in frequency through better survival and reproduction, the fittest-variant survival mechanism is the correct description of Darwinian evolution.