Genelle:  You've done a lot of excellent research, and I see you've
already heard from the real expert in this field, Dr. Dettwyler herself (I
strongly recommend that you and your friend read her chapter "A Time to
Wean" from Breastfeeding:Biocultural Perspectives).

I just wanted to add that there is another important aspect of "prolonged"
or "extended" (read NORMAL) nursing:  benefits to the mother herself.  The
studies which have shown a decreased risk of breast, ovarian and uterine
cancer, although somewhat inconsistent, generally show that longer
duration of breastfeeding has more of an effect.  This may also be true of
reduced risk of osteoporosis.

We breastfeeding advocates sometimes get so involved in telling women how
good breastfeeding is for their babies, that we forget to tell them how
good it is for them as well.  Hope this helps, Alicia Dermer, MD, IBCLC.