Darwin and Wallace both studied changes in organisms over time. Their theory of "decent with modification by natural selection" was unprecedented because it:

a. rejected the idea that species are fixed and emphasized the importance of variation and change in populations
b. was the first theory to refute the ideas of special creation
c. rejected the idea that species vary and emphasized the importance of the fixation of change in populations
d. proved that individuals acclimated to their environment over time
e. was the first time a biologist had proposed that species changed through time