I think that's a fallacy. 1 in 4 women died in childbirth. In Rome (the city), men were 10 times more numerous than women. I don't know of any period in which women were more abundant than men, except for today.
Today is the first time in Sweden when there are more men than women, and a search in Swedish church books shows that there were a female surplus of up to 13% during the period between 1750 and 1850, and earlier on, during the 17th and early 18th century, the surplus was even larger, in some villages there were twice as many women as men. During the 1890ies the female surplus in Sweden was 150.000 women.
http://fof.se/tidning/2015/6/artikel/nu-ar-mannen-fler-kvinnorna One reason for the female surplus in Sweden during the 17th and 18th century was that Sweden was involved in wars on the continent and later on in Russia. Young men were conscripted and left Sweden while the women stayed, and many of the men never came back, they died or became prisoners of war in foreign countries. The same story is true for many other countries that has been involved in wars on foreign ground, take all those soldiers Napoleon took with him to war, in antiquity there were Alexander and his men marching east, as well as the crusaders later on.
Yes, it's true that many women died in childbirth, but very often the widowers remarried, it can be considered as a kind of polygamy, even if there isn't more than one wife at the time.
As for Rome, when in history were there ten times as many men as women there? Of those men, how many were soldiers and how many were slaves, and later on how many were priests? Not all men were able or permitted to marry, and it wasn't always that men and women were at the same places. If there is a surplus of men in one area, there is most likely a surplus of women somewhere else.
