Elven biology, by an amateur
I've been thinking about elves and men. How comes that elves are immortal and men aren't, when (a) elves came first, so are, in a way, a trial run; and (b) elves and men can have children together? Now, I know nothing about biology except what I managed to forget after school, but the elven immortality looks like it comes from their body tissue being more durable, so it lasts longer and renews better. Also there should be some differences in muscle and bones, allowing them more flexibility and more strength with lighter body build. So, differences in body construction and tissue construction, but not enough genetic differences for cross-fertility to be impossible (no, I don't know whether this is technically possible).
So, why men, then, and why these differences? I think that it must be related somehow to elves having fewer children. Perhaps Eru decided that immortals have to have limited number of children or maybe their differences somehow make for lessened fertility. And the resulting number of elves turned out not to be satisfactory. Maybe Eru wanted more of Arda settled, who knows. So, the tissue durability is taken out of the new model; and maybe body differences too - perhaps otherwise mortals would make too many risks. So we have men, mark 2, so to say.
The only question this hypothesis leaves out is the one of the half-elven. How are they able to choose? Perhaps they have a more elven body build, but each cell has both types of development, durable and not-durable, which lie dormant until the time of choice and require a mental command to be switched on and off (and that must be an elven trait, since elves can make their bodies die at will).
And probably that makes no sense whatsoever, but I can't remember if these things were discussed in Tolkien's work.
So, why men, then, and why these differences? I think that it must be related somehow to elves having fewer children. Perhaps Eru decided that immortals have to have limited number of children or maybe their differences somehow make for lessened fertility. And the resulting number of elves turned out not to be satisfactory. Maybe Eru wanted more of Arda settled, who knows. So, the tissue durability is taken out of the new model; and maybe body differences too - perhaps otherwise mortals would make too many risks. So we have men, mark 2, so to say.
The only question this hypothesis leaves out is the one of the half-elven. How are they able to choose? Perhaps they have a more elven body build, but each cell has both types of development, durable and not-durable, which lie dormant until the time of choice and require a mental command to be switched on and off (and that must be an elven trait, since elves can make their bodies die at will).
And probably that makes no sense whatsoever, but I can't remember if these things were discussed in Tolkien's work.