Plutarch, Quaestiones Romanae
Goodwin, Ed.

Solution. Perhaps it's a natural reason, that girls are forwarder, for the female grows up and comes to full stature and perfection before the male. But they take the day after the seventh, because the seventh is dangerous to infants by reason of the navel-string; for with many it falls off at seven days, and until it falls off, an infant is more like a plant than an animal. Or is it, as the Pythagoreans reckon, that the even number is the feminine, and the odd number the masculine? For it is a fruitful number, and excels the even in respect of its composition. And if these numbers be divided into units, the even, like a female, hath an empty space in the middle; the odd number always leaves a segment full in the middle, wherefore this is fit to be compared to the male, that to the female. Or is it thus, that of all numbers nine is the first square number made of three, which is an odd and perfect number, but eight is the first cube made of two, an even number; whence a male ought to be square, superexcelling, and complete; but a woman, like a cube, constant, a good housewife, and no gadding gossip? This also may be added that, as eight is a cube from the root two, and nine a square from the root three, so the female makes use of two names, and the males of three.