Another reason for goblins not being related to Falmer; If Goblins were discovered to be of Elven blood, their Altmer trainers would kill them all since they would be elves of impure blood.
I'm starting to think that the Altmer, far from being so frivolous with Merrish life, don't actually euthanize their defective babies.
They just paint 'em green and ship 'em off for Goblin-boot-camp.
I did a search for "fertility" on TIL. Apparently it comes from a single line of dialog in Morrowind. I'm inclined to say that puts it on the same level as the argonian life-phase, but even if it doesn't, the Altmer could easily manipulate the conditions of their fertility. One easy technique: wage war.
It does make sense, in any case, for longer lived organisms to reproduce less. If the Altmer, who can easily reach 200, were to be not just perennially fertile but
fecund, the population strain would be of several thousand magnitudes past 'totally Malthusian apocalypse'. Ecological collapse, mass starvation,
overcrowding, urban squalor, crime. All very un-Altmer.
The high-folk are static, anuic. They aren't given to the chaos of men because they don't suffer the same population burdens. Men aren't always at war just because they feel like it, they need lebensraum.
Also, wars deplete populations. I can't imagine a total war being good for anybody's birthrate.