商品簡介
It is said that "necessity is the mother of invention". To be sure, wheels and pulleys were invented out of necessity by the tenacious minds of upright citi- zens. Looking at the history of mankind, however, one has to add that "Ieisure is the mother of cultural improvement". Man's creative genius flourished only when his mind, freed from the worry of daily toils, was permitted to entertain apparently useless thoughts. In the same manner, one might say with regard to evolution that "natural selection mere(y tnodifted, while redundanry created". Natural selection has been extremely effective in policing alleHe mutations which arise in already existing gene loci. Because of natural selection, organisms have been able to adapt to changing environments, and by adaptive radiation many new species were created from a common ancestral form. Y et, being an effective policeman, natural selection is extremely conservative by nature. Had evolution been entirely dependent upon natural selection, from a bacterium only numerous forms of bacteria would have emerged. The creation of metazoans, vertebrates and finally mammals from unicellular organisms would have been quite impos- sible, for such big leaps in evolution required the creation of new gene loci with previously nonexistent functions. Only the cistron which became redun- dant was able to escape from the relentless pressure of natural selection, and by escaping, it accumulated formerly forbidden mutations to emerge as a new gene locus.
