The theory that focuses on parents pressuring males to be
more masculine and females to be more feminine is the parental imperative in
which is focused on gender identification of an individual that is being
maintained in order to ensure the survival of one’s children.
The 25 000 is a good tip: what happened then?
It was the time of the last Glacial Maximum (Ice age). So either the Bering Strait was frozen over at the time, or the sea water was lower because so much water was taken up by the glaciers (or, most likely, a combination of the two).