Or, it must be possible to support some kind of reasonable family life on less than two full time incomes.*

* This does not mean "exactly one full time income", aka "woman, get in the kitchen". There are many desirable options between "one traditional full time male earner" and "two people working a combined 90 hours of paid employment". Also doesn't necessarily mean all the trappings of an affluent Western lifestyle, big suburban home with two new cars on the drive, foreign vacations every year etc.