There's a lot of other studies about different passive fertility in forager groups that bear out the cross-cultural applicability of the San studies as well. Forgot to add that.
Studies of forager groups on several continents have come to the same basic conclusions around that. Some of those findings are summarized here: http://books.google.com/books?id=grrA421tRNkC&pg=PA431&lpg=PA431&dq=foragers+and+menarche&source=bl&ots=WNuoQO-gYV&sig=h1ahBo5ApBv4Q9uYxD47pM_whNM&hl=en&ei=NtBNTpzkFeOssALYip3rBg&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDAQ6AEwAg#v=onepage&q=foragers%20and%20menarche&f=false
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: