Has anyone read anything about birth order and enneatype, regarding any consistent correlations? Any books to recommend, or links to share? What brings this to mind is I was wondering the other day if e8s tend to be older siblings, but I'm curious about whatever correlations exist for any type.
I'm also wondering about instinct variant. I'd be surprised if birth order played much of a role in variants, though I am curious about similar stackings between siblings.