Originally tiny mythical beings, elves have become a clichéd race of pointy-eared, arrow-slinging, forest-loving, effeminate warrior mages that populate every unimaginative stab at fantasy storytelling. Recent mutations look like dumptrucks.
The elves have undergone some serious changes of late. Early examples of the species tended toward being small, ineffectual, and annoying. They spent a great deal of their time bothering humans with pranks that ranged from annoying (souring your cow's milk) to "beyond Punk'd" (luring horny young men into remote locations and killing them). Medieval peasants would likely have lumped them into the same category as rats and stray dogs, if they weren't so busy starving to death and being oppressed by royalty.
It appears that elves began to develop a more cohesive society somewhere around the 16th century, ultimately electing a King (Oberon) and a Queen (Titania). While they were still a mixed lot of smelly, grimy little freaks, they were at least starting toward what we usually think of as an elf (prior to World of Warcraft fouling all that up (see below)).
Based on Shakespeare's "A Midsummer Night's Dream," Fussli's "Das Erwachen der Elfenkonigin Titania" depicts elves as most renaissance Europeans would have encountered them: goat-horned little drunkards dressed like they're one step away from a classical Greek orgy. Note that some common "elven" features became the norm in this period: pointy ears, flowing fabrics, and a borderline-sexual love of trees and woodland animals.
The Minor Elf
Toward the end of the European renaissance, it appears the elves diverged into two distinct sub-species. The first consisted of the smaller, craftier elves, the kind that enjoy building toys or baking cookies. They maintained their predecessors' small, plump, ugly appearance, but they appear to have moved away from the habits of kidnapping peasant babies and killing livestock.
It is common knowledge that Santa Claus has been breeding and enslaving the minor elves for his North Pole "workshop" for centuries. No one knows where he captured his original stock, but some people have speculated that he took his reindeer sled to some isolated South Pacific islands in the 1600s to find mating pairs. (The big red sack hasn't always been used to transport toys...)
Mr. and Mrs. Claus took the chihuahua approach, selectively breeding their elves to be as small and amenable to training as possible. They attached bells to their hats and boots in order to more easily find any runaways on the vast emptiness of the North Pole. This is also why they are dressed in bright reds and greens: the better to stand out against the white snow.
The Keebler Elves were discovered in 1969; they are a reclusive group of baked-good artisans that appear to have built their commune inside a large hollow tree. While there were two female elves discovered there (Ma Keebler and Flo the accountant), the community is otherwise entirely composed of "artistic" men. Anthropologists have since suggested that this group was driven out of or left a larger elf community in search of sociological freedom.
Sadly, the lack of sexually reproductive partners have led to the slow decline in the Keebler Elf population. They have since been put on the WWF endangered species list, and will likely be extinct by 2013.
The Major Elf
While the minor elves were being enslaved by Kris Kringle and hiding in hollow trees, the other branch of the elf family, the major elves, enjoyed a surge of popularity because of the writing of J. R. R. Tolkien.
Tolkien describes the race in his Middle Earth tales (most notably The Hobbit and The Lord of the Rings) as beautiful, elegant, immortal warrior-poets. They're interested in archery, lore-making, architecture, and orc-disemboweling. While solid soldiers, these elves tend to be a bit on the delicate side, preferring to fire arrows from a distance while invoking ancient spells and whatnot.
Later fantasy writers shamelessly "borrow" from Tolkien's anthropological studies, choosing to describe the major elves verbatim instead of coming up with anything even remotely original.
The major elves appear to have taken control of their image during the unfortunate rise of tabletop gaming. Recent investigations suggest that Titania and Oberon approached Gary Gygax while he was making the first editions of Dungeons and Dragons, pushing for their inclusion as a noble race of spell-wielding badasses in return for the occasional rendezvous with an elf maiden.
(It should be noted that when the dwarves offered a similar deal to Gygax, they were initially turned down due to the "quality" of the dwarf maidens.)
Any further discussion of the D + D elves is entirely irrelevant, since anyone that still cares about them will already know their preferred classes, armor restrictions, health bonuses, spell bonuses, attack bonuses, masturbation bonuses, and whether or not they can breed with gnomes. And really, only social recluses play Dungeons and Dragons anymore. If you own any dice with more or less than six sides you've killed any chance you had at mating.
Thankfully, the increased availability of personal computers and home gaming systems all but killed off tabletop gaming (small pockets still exist in the rare overlaps of nerds and technophobes), allowing the major elves to focus their image concerns on a new genre: the video game.
The major elves continued to look the same throughout the rise of the videogame, becoming a standard race in every fantasy game ever released (although occasionally under an inexplicably different name). Warcraft 2, Oblivion and Dragon Age all show the consistency of the elves' image.
They maintained their usual dimensions as skinny, graceful, and endowed with pointy ears, and they were most often used as thieves, scouts, rangers, archers, or the objects of intense, homoerotic fanfiction.
The World of Warcraft Shift:
A major evolutionary shift occurred around the time of the World of Warcraft explosion. Gaming in general had taken a turn toward the absurd, with characters becoming more and more swollen with impossibly huge muscles and increasingly tiny heads. (See Gears of War, Unreal and Batman: Arkham Asylum.)
Perhaps afraid that they would appear anemic and effeminate next to these behemoths, the elves have taken the Scott "Carrot Top" Thompson approach to overcompensation, packing on unnecessary bulk to become something that looks more "cave troll" than "Legolas" (read "gay").
In fact, the only thing that seems to be carried over from their woodland origins is a pair of pointy ears that have now been so damaged by the steroid use that they have grown out of all control. We can only assume that their HGH abuse is the cause of those eyebrows as well.