> Does it provide a source for that figure? 4% seems pretty small. 

Thanks to Philip and Todd for reminding us that this figure is probably way too small.  I had forgotten that point and would love it if someone could dig up the study that supports it.  But it wasn't really my original reason for posting.  Hobbes may have had it very wrong.  It's a lovely thought, really, that perhaps life in nature wasn't "nasty, brutish."  And, yes, maybe it wasn't "short" either.

Jim