Peter Leithart passed on Paul Stephenson’s contentions about why Christians grew numerous in the Roman Empire: the requirement of husbands’ faithfulness to their wives, the forbidding of anal and oral sex, and the rejection of abortion and infanticide.
Infanticide often targeted girls in Rome. Leithart here quotes Stephenson’s book Constantine:
“If the population of the Roman Empire was sixty million at the time of Constantine’s birth, only around twenty-four million of these were women. Given that boys are more problematic in the womb, more sickly and more inclined to die at a young age in military activity or by violence, this figure is quite remarkable and can be explained only by the fact that baby girls were frequently murdered.”
He goes on: “It was rare for all but the wealthiest families to raise more than one daughter, however many were born . . .
“and infanticide was the surest way to dispose of unwanted girls. It was legal, philosophically justified and widely practiced. An infamous letter sent by a man to his pregnant wife in 1 BC instructs her: ‘if it’s a boy keep it, if it’s a girl throw it away.’ . . . far fewer girls than boys were allowed to grow to maturity, that is to child-bearing age, and consequently the general rate of reproduction in the late Roman world was kept artificially low.”