Assuming normal human genetics any such imbalance will be temporary and due to extraordinary circumstances. An example would be Paraguay in the 1870's; the War of the Triple Alliance (1865-1870) had led to the deaths of more than half of Paraguayan adult males, creating a huge imbalance toward females. (The 1871 census listed 221,079 people: 86,079 children of both sexes, 106,254 adult females, and 28,746 adult males.) Even one hundred years later females outnumbered males there significantly; however, as of the present date the ratio is a normal 51 males to 50 females. So a ratio of nearly four females to one male has returned to the normal equality in one hundred forty years.