I get the purpose of the movie

i get that the scientists goal was to preserve life by placing his life force in each doll and give them each there ouwn souls also its implied that atleast some of the Dolls had to die for it to rain Bacteria for life to be reborn. but what i do not get is why did he choose Dolls

if he has the scientific know how and the knowledge of alchemy to build living dolls could n;t he have just built him self some Frankenstein monsters that could be programmed to bone and bring life back that way instead the manner in which he did it with the bacteria will take billions of years before life repops up