Peter asked
> Wasn't the geography also a factor? Deeply divided valleys,
> heavily wooded, making movement difficult. No wonder so many
> tribes or "tribelets" developed. The PNG situation cannot really
> be compared to areas with a rather different geography.
I doubt it. Also in the PNG case there seems to have been
a "diversity selection" factor operating at the heart of most
tribes. Tribal warfare was such that most people lived and died less
than 10km from their place of birth (long distance trade was always
through the hands of intermediaries except in exceptional
circumstances (eg there is pre-contact stories of Kagua Anggal Heneng
people moving to Kikori and of Koroba Huli moving as far south as
Mount Bosavi).
Regarding "diversity selection" it operates at the level of vegetable
cultivars as well as human languages too. It is known, for instance,
that sweet potato has only been present in Papua New Guinea over the
last 350 years. And yet the Herbarium at Aiyura has a collection of
over 400 cultivar varieties and French has shown that this impressive
collection represents about 0.5% of the total number of genetically
distinct varieties of sweat potato in the country (giving a
staggering total of 80,000 different varieties).
Given that amongst many tribes, male initiation cults encourage the
development of a wholly new language limited to one's age mates (and
unintelligable to one's elders) - the speed with which new languages
develop can be put down to more factors than lack of markets,
geographic isolation or shifting subsistence lifestyles.
Regards
John