For CivilLies: While I cannot speak for the author I believe that it is a reference to the different methods used to conceive. 1-Was the natural way with sex. 2- Was by fertilization, where they insert multiple fertilized eggs to increase the chance of success. Which usually leads to multiple babies. and 3- Not sure, could be just a parody, an exaggeration. Or it could be a metaphor for the population explosion. In the last 100 years we have produced more people than all the years previous combined.