While that sounds kinda logical, why then does Katherine Dettwyler put the
natural age of human weaning somewhere between 2.5 and 7? That's such a huge
variation.. it seems odd that 6-7 year olds could have the right shaped
mouth and my three-year-old doesn't. Hmm, perhaps this is just an extension
of her playing with her food :-p

well some children may wean for other reasons, but I don't think the
range is that implausible, I mean some newborn babies have genuine
problems with breastfeeding due to the shape and muscle tone of their
mouths - thankfully they can usually be helped by an occupational
therapist with relevant experience and training. Every mother/child pair
is different, each mother is going to vary at what point the latch
causes discomfort and when the stimulation changes to the point of very
little milk being produced and each child is going to vary on how much
milk is worth it and so on, so many permutations that will give a wide
variation in age.

Cheers
Anne