When Adam Smith wrote The Wealth of Nations, he noted that although the wages of the lowest classes were oftentimes determined by the lowest their employers could pay, humankind's present population acknowledges that at large, even with an imbalance of wealth, employers could not sustainably pay their workers less than would maintain a family of four (Book I, chapter VIII). If employers were to seek to pay less, then populations would shrink until competition over labor would force the wages of even the lowest classes higher. And since the population of the world is now greater than in past years, especially considering that Western societies are generally monogamous in terms of marital structure, then the poorest working classes must have been able, even without minimum wage regulations, to afford families of five and greater. If this was not the case, then wealthy families would have been primarily responsible for the present population -- a highly unlikely scenario, considering even Smith acknowledged that wealthier women were less inclined toward childbearing.
Adam Smith, eh? So Henry Ford read his book.
In any case, another source seems to confirm Smith's theory.
The author of the linked article goes on to compress all of the old Rockford Institute's work (Allen Carlson, not the current occupants) into a few grafs.
He's right, you know.