Two thoughts that suddenly got connected.
Thought 1:
In Appendix A of The Lord of the Rings we learn that in his youth Aragorn journeyed through Rohan and Gondor and won fame under the name of Thorongil. (LR A.1.iv.63-67.) He made quite an impression on the people of those countries at the time, but a few decades later things are different. We don’t hear of any old men in Rohan who recognize him, even though he rode with Thengel, father of Theoden. Denethor apparently recognizes Aragorn through the image in his palantir, so his appearance can’t have changed too much. But then Prince Imrahil, who is of similar age, says “Shall we not now send for the Lord Aragorn?” when Aragorn is standing a few feet away. (LR 5.08.041) Imrahil doesn’t notice him until he speaks.
But here’s the thing – Aragorn is “at least 6 ft. 6.”. 1 Even great warriors like Boromir aren’t that tall. 2 How is a bean-pole like Aragorn not immediately recognized by everyone over the age of 50? His reception in Edoras should have been less laden with suspicion, and more like, “Eala, Thorongil! Long time no see! How’s the weather up there?”
Thought 2:
The odd shrinkage of Elves. Medieval fairies could be small, or very large, or human-sized. “Taking the broadest known parameters, we find that size can range from fourteen feet high to a being small enough to sit on a cowslip.” 3 Victorian fairies are uniformly tiny, though. Tolkien wondered about this in “On Fairy-stories”. 4
As for diminutive size: I do not deny that the notion is a leading one in modern use. I have often thought that it would be interesting to try to find out how that has come to be so; but my knowledge is not sufficient for a certain answer.
The Professor goes on to speculate that elves started to shrink during the Age of Discovery, when Europeans sailed all around the world and found no Faërie anywhere. In order for Elves to continue to be a thing people could believe in, they needed to be able to hide from view. It was advantageous for them to shrink. The process was exactly parallel to evolutionary pressure: just as squirrels are now the right size to fit through the holes in a chain-link fence, Elves met the challenge by shrinking until they could hide practically anywhere, even behind garden flowers.
Synthesis:
Evolution by natural selection is tempting, but it is fraught with difficulties when we’re dealing with immortal creatures. Fortunately, there’s an easier answer, provided by Tolkien himself. The way the cloaks of Lothlorien hide you from view must be to make you look short. Otherwise, there’s no way Aragorn could have maintained his anonymity while standing half a head above everyone around. Apparently it’s not just Galadriel and her maidens who can make those; it’s a common skill among Elves. Maybe it’s the only way they know to make clothes. It also explains the cloaks’ preternatural effectiveness in getting Sam and Frodo to Mount Doom — knock a foot off the perceived height of hobbits and they’re just barely macroscopic.
I’m not just making this up. Let’s jump over to “Smith of Wootton Major”.5 Alf’s dramatic revelation at the end:
’Would you spare a few moments for the King of Faery?’ the other answered. To Nokes’s dismay he grew taller as he spoke. He threw back his cloak.”
In 1939, Prof. Tolkien’s knowledge was not sufficient, but by 1967 he had figured it out.