Silly but simple thought experiment: - 10 people on an island - 2 people can pick enough coconuts for all 10 to eat well - Using a ladder, productivity picks up enough so 1 person can pick enough coconuts for all 10 - A coconut picking robot is developed, picking enough coconuts for all 10 The coconut picking robot's productivity can't scale indefinitely but it doesn't have to.
I am sure you can see the implications of using robots in the real world.
Edit: Speaking of babies, prof. Hans Rosling's TED talks are mandatory. http://www.ted.com/speakers/hans_rosling http://www.ted.com/talks/hans_rosling_religions_and_babies
Anyway, I think the first people to lose their jobs would be the ladder makers.
Second, China solved the overpopulation problem quite well with the one-child policy (maybe too well, even).