Well heres what I know about the Elderlings...
The Elderlings are probably one of the rarest speices on Oddworld, infact the Rasin is the only known one to exist on Mudos. They spend most of there begining years as Elderling trees (first 6000 years to be exact) as Max said. During these years they become more intouch with nature and see many interesting events play by, such as Wars, Death, Birth, Forest Destruction, Navtive village destruction, the formation of "Abe's" moon, and many other things. Its because of all this that happens before him that the Rasin is so wise.
Once they grow pass the 6000 year mark they go to thier third stage which is what we see the Rasin in today. At this stage they begin to master their meditation methods, learing how to free themselves from thier body and explore Mudos. Our Rasin particularly loves to look through the eyes of a newborn. The Rasin has looked into the personal lives of every inhabitant on Mudos, its because of this that he is able to feel compassion for
every creature on Mudos (yes even the Glucks, Sligs, Vykkers, and Interns, etc.). If you look at his skin you can still see what looks to be a pattern of Elderling tree bark, and his small stubbles at the bottom of him where his once gicantic roots.
Sorry if you wanted Max to answer this Im just trying to boost my reputation and gain some sort of Oddworld Knowlege title, like Max and Kanzumer. *Sigh* but I guess that will never happen.