The impact of human fertility cycles ("concealed ovulation’) and human evolution is a vast, deep field of study and speculation in itself, but I am making some very sweeping generalizations here, referencing people’s capability to choose when to reproduce on the broadest levels, not that there was a period or specific instance of this having an impact… more like, it made a difference over very large scales of time, as evident by the fact that our breeding cycles are nothing like most other mammals.