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