: Doubtless this has occured to some-- what about the barren-ness
: or relative infertility of the Elven race? After all, living
: thousands of years, most Elves only have one or two offspring.
: So what's up with birth control?

Well, actually, they averaged about four children per couple in the "early years" (Tolkien doesn't tell us when they started having fewer children, but I suspect that didn't begin until sometime after the middle of the Second Age, and probably varied from group to group).

In one of the essays Tolkien says that each time an Elf is conceived, some part of its parents goes into it. This is why Miriel was "burned out" by giving birth to Fëanor. He got more of her than a child normally inherited. But eventually, in normal reproduction, the parents eventually stopped having sex as their interests turned elsewhere. So you can say the sex drive diminished with each conception.

: Naturally these questions have not been deeply explored by
: JRRT.

Oh, but they were! :)

: Nevertheless, let me hazard one extrapolation for the board:
: Elven sex was a rare event, occuring no more frequently than
: pregnancy among the Second-born.

I suspect it occurred more often than that, but it evidently dropped off after enough children were born.

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Parma Endorion: Essays on Middle-earth, Revised Edition