continue: The "modern synthesis" of genetics and Darwinian evolution involves mutations, variation caused by gene rearrangement, and natural selection. >New variants of genes added to population through mutation - caused by mistakes in replication, UV and radiation, and transposons. >Recombination of genes by segregation and independent assortment produce an almost limitless number of possible genotypes and thus a very large number of possible phenotypes. >Randomness and small steps of variation produced by recombination are necessary conditions for natural selection to operate. Otherwise, selection is simply an "executioner". >Particulate inheritance - no loss of variation from generation to generation. Recessives don't get diluted out. >Natural selection favors the "fittest" individuals, those phenotypes which produce the largest number of viable progeny which mature and reproduce. Because the phenotype carries with it the genes which specify its phenotype, these genes are passed on preferentially and become most common. from web link: //www.bio.miami.edu/tom/courses/bil160/bil160goods/03_darwin.html