[Smokin' Joe]

There was an elephant bone found on the Iberian Peninsula a few years back which had carved into it seven marks one way, 21 marks another way. While the anthropologist who was describing it said it 'was obviously of great religious significance', I laughed and said "It's a calendar"!

In the '70s Psychology Today had an article on a study done on groups of college women living in the same group (dorms and sorority houses). It turns out that those groups tended to synchronize their lunar cycles.

If the same phenomenon existed within tribal units, ...

I guess there was one week a month when it was preferable to go out and risk your life attacking huge beasts with pointy things rather than remain in camp...

[21twelve]

You might be right! The calendar on our kitchen wall has those glyphs for the three females in my house. Of course I can’t really schedule out-of-town projects around it!

[gleeaikin]

It would make sense for a nomadic tribal group to have all the females with synchronized lunar cycles. The wandering tribe could camp for a few days while the females did their thing, and the younger men could go off hunting unencumbered by slow moving women, kids and old folks. Also not staying in camp with no female “entertainment” available. It sounds like an evolutionary win-win solution.