fascinating post about great apes and when they wean.
Of course there is variation between the species, but they all nurse until at least 3 years, and some routinely nurse until 5 or 6 or even 7. Their biological development is similar to ours (how and how long it takes the brain to develop for example), so then logically humans' "natural" weaning time is probably in a similar time frame.
I'm not saying that we all need to nurse our kids until they start kindergarten, but I do think the oft-preached practice of weaning at 12 months does a great disservice to the average child (and mother). My plan was always for 2 years. I nursed Bear several months longer than that because he wanted it, but weaned him at about 2 1/2. At 12 months old he was actually still consuming more breastmilk than solid foods--it would have been hard on both of us to make him give up his primary source of nutrition. Besides which, the older a child is when he is introduced to a new food, the less likely it is that he will have an allergic reaction to it.
Eagle I will nurse until we reach some mutually agreeable age--it will probably be around 2 as well. There is a huge difference in the maturity of a child between age 1 and age 2, both physically and emotionally. So that is why I continue to believe in extended breastfeeding.