Now that I know from context what "tanistry" means....
.... that's an interesting observation,
Ang. What would one expect such long life to have to do with hereditary rights?
Imagine that you are a 1,000 year old Elf and you have a brother who is a mere 200 years younger than you, and your father is roughly 1200 years older than either of you. While there are battles and warfare, there is no guarantee that father is going to die and pass on his realm to his first son any time soon. It could take a nother couple thousand years. So what do you do? What do you do if you're the second son? I know what I would do: I wouldn't wait around, I'd go and seek to create a new realm for myself where the Elvish population is sparse. But Tolkien's Elves didn't do that so much, did they? They stayed in the realms of their fathers and did'nt even wait - rather, it was as if they hoped never to become the hereditary ruler of their father's realm, for who wants father to die? What a strange situation....