Earlier quoted context omitted.
That evolutionary instinct came from a time when humans lived in communal support networks and new parents had help from extended family, and does not translate well to a world where Mom has to work 9-5 in an office a few months after birth. You might as well express shock that suburbanites don't supplement their diets by foraging for fruit and mushrooms. Besides, it's not like parents 10K years ago had the option to…
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This is not a US phenomenon, it's pretty much a global phenomenon by now. It's the flip side of breaking down the traditional family/society model - as more and more households had two incomes, the market quickly compensated for the surplus, and now most households struggle without two incomes.