| Human females are the only one's to go into heat every 28 days. All other mammals have a completely different, almost opposite way. Take my female dog for instance; she goes into heat every 6 months for a one week period (sic). During that week, she is very interested in sex and can become pregnant about 5 days into her cycle. She also bleeds during this entire process.
As far as I know, human females are the only mammal to almost always be receptive to sex and get pregnant between their oestrus periods. Receptive meaning they can decide whether they want to or not (comment made to appear PC, as my experience is that many more factors such as plausible socially available identity on the part of the male plays as much of a role in whether sex actually occurs).
That thing about women getting into sync with their cycles is probably a hormonal thing. Not sure what the evolutionary advantage was, but I theorize it was to be available at the same time as the others, maybe to coincide with the return of the hunter-male groups. Party time!
To answer an earlier response, yes male humans do have one less rib, or more precisely, an atrophied rib where the human female has the whole thing.
I am amazed at human inventiveness, where the whole concept of Adam's rib was posited to explain this enigma. Personally I like the earliest explanation, credited to the followers of Mithras, that the missing rib needed to be used for other, boner, purposes. :-) |