There is nothing stating the changes can not be abrupt .... adapting to some kind of environmental change .. and there has been no sinking of the survival of the fittest theory .. and we do see rather gradual evolution in many cases .. just because there are links and gaps does not sink evolution. .. its not like you find everything over a billion years .. stuff gets wiped out.
In particular we see a large degree of evolution in humans over a relatively short period of time Neanderthal to Homo Sapien. Survival of the fittest is reality in proper context .. taken out of context you have Eugenics