Great points fearn!
Just something I'd like to add, if it means anything
Originally Posted by fearn
In the tropics, moisture is a huge issue. This keeps archers from using horn for compound bows (since it messes up the glue and promotes rot of all materials). Even drying the bow wood to get maximum performance is impossible. There are two ways around this: making huge wood bows (as in South America and Papua New Guinea), and using smaller, weaker bows but poisoning the arrows. I know the latter was used by the pygmies and others, and from the pictures above, I'll bet the former was used as well.
Moisture is a problem... Most Amazonian natives replace their longbows every year, and the bowstrings frequently. Daily use combined with moisture make it necessary.
One exception to the moisture negating horn is Java. I believe the Javanese had horn bows made with water buffalo horn. However modern Javanese competition archery uses wooden recurve bows. Here's an article from ATARN
(an excellent Asian traditional archery site). However it wasn't like a composite bow, it was two horn slats joined at the grip with a wooden(?) grip strapped on, I think
Only other culture I know of who made horn bows (not like Asiatic composites) were the Shoshone and maybe some related tribes... using mountain sheep's horn. Very powerful compact bows.