You're implicitly assuming that production is "hand-bound". It could also be bounded by natural resources. For example even if the number of mouths to feed inc

You're implicitly assuming that production is "hand-bound". It could also be bounded by natural resources. For example even if the number of mouths to feed increases, the number of farmers cannot increase beyond what there is farmland for. So the hands will be competing for who gets to plough the fields, in exchange for a meal. Too many hands along with too little land, and the losers starve.