Oh no don't say we're straying into Chris knight teritory and his theories of women being amphibious.

Any idiot can face a crisis - it's day to day living that wears you out.

It is purely coincidental. The lunar cycle is slowing down. A billion year ago, it was much shorter, may be just 16-20 days, I can't dig a link right now. The Earth-Moon system is gradually transforming its angular momentum from close&fast to far&slow (it's a tide effect, and at the same time, tides and other planets dissipate some of this momentum, but there is also a transfer from the rotation of the earth).

And the Earth days themselves are slowing down, they had fewer hours a billion year ago.

The Moon is already tide-locked with one side watching the Earth. Eventually if the system could go on long enough (it won't, the sun will blast it all earlier), the Earth would also become tide-locked with the moon, with a day that last weeks and the Moon further from the Earth than it is now.

And anyway, it's only western women who have a 28 days cycle, found this looking for a ref. on wikipedia:
http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=1340049&dopt=A bstractPlus

Pierre

It needn't be coincidental (although it may be). Nor does it need to be about tides.

City life and brick and mortar dwellings have made us unaware of a very basic aspect of the moon cycle : a full moon means lights. Which may have had very practical effects in the way of life of your basic hunter-gatherer tribesman, especially pre-fire.

The fact that women's cycles are very variable means the adaptation could have been a weak one ; and that synchronisation within the tribe may have helped to adjust the cycles to the moon's cycles. And maybe the synchronicity happened only because once a yearly cycle was too long for reproductive success, another rythm was needed - and the one given by the moon was fairly convenient for biological purposes.

Un roi sans divertissement est un homme plein de misères