Rather bad explanation...

...yet informative, I'm here referring to Vlog 8.
The thing is that it's really easy to explain: it all depends on the genes, if a gene is recessive it will become rare over the ages (in one species) but when it is dominant it will remain intact and will be visible there.
So when in a normal household the more recessive Elf genes will be preserved because there is nothing more dominant to suppress them. In a combined household however, let's say human (since I don't remember the new name) and elf, the 'weaker' elf genes (like the youth genes) will be suppressed by the 'stronger' dominant human genes, so the child will have more characteristics of a human then of an elf. Simple.
That explains everything you explained about that in the Vlog.
(

Druidic Society?

Once chosen the looks and size of the elf, the next question I ask myself is, would they have a feudal or a druidic society?

Feudal: You know how it goes... it is the typical human model with kings, princesses, knights and the like. The classical noble elf, pretty and long-lived but with very human passions.

Druidic: A society that is not centralized, with some kind of religious belief in the base but no one person or group with oligarchic or religious control. The belief in "the natural order of things" would be so deep to eliminate the need for politics. People picks a job in base on their skills and likings, everyone shares. Utopian society in which everyone is happy and cared for. No personal cravings allowed or tolerated...

I'd personally go for the second option, as I find it more interesting/characteristic than the first. This would by the way cause elves to shun any kinds of destructive or polluting technology although they may have no problem with the cleanliness of gearwork gadgets. Also they would be likely to become rangers, healers and alchemists.

Which type of elf?

Originally, in the Norse/Germanic mythology, the elves were conceived as powerful and beautiful human-sized beings. In addition to these human aspects, however, they are commonly described as semi-divine beings which are not bound by physical limitations and could pass through walls and doors in the manner of ghosts.

The influence of Shakespeare later made the use of elves as small beings the norm. In Victorian literature, elves usually appeared in illustrations as tiny men and women with pointed ears and stocking caps. These are probably the same kind of elves as the little "Christmas" elves, skilled engineers with with long noses, and pointy hats.

On the other hand, Tolkien's elves tend to be taller, more beautiful and wiser than humans, with sharper senses and perceptions, facial hair, and long and pointed ears and great aptitude for magic although not magical creature themselves and thus bound to the regular laws of physics.

So I wonder... what type/size of elf is it that you are thinking about?

- Will they be smaller/taller than humans?
- Will they be so naturally powerful as "magical creatures" to be able to seemingly bend the law of physics? (e.g. levitate / walk through walls?)
- Will they be skilled engineers (like the "gnome" kind of elf) or substantially rely on their magical skills and actually shun/dislike technology as something unnatural and possibly evil?

"Standard" Elves

ELVES:
Elves mingle freely in human lands, always welcome yet never at home there. They are well known for their poetry, dance, song, lore, and magical arts. Elves favor things of natural and simple beauty. When danger threatens their woodland homes, however, elves reveal a more martial side, demonstrating skill with sword, bow, and battle strategy.

Personality:
Elves are more often amused than excited, more likely to be curious than greedy. With such long lives, they tend to keep a broad perspective on events, remaining aloof and unfazed by petty happenstance. When pursuing a goal, however, whether an adventurous mission or learning a new skill or art, they can be focused and relentless. They are slow to make friends and enemies, and even slower to forget them. They reply to petty insults with disdain and to serious insults with vengeance.

Physical Description:
Elves are short and slim, standing about 4
1/2 to 5 1/2 feet tall and typically weighing 85 to 135 pounds, with
elven men the same height as and only marginally heavier than
elven women. They are graceful but frail. They tend to be paleskinned
and dark-haired, with deep green eyes. Elves have no facial
or body hair. They prefer simple, comfortable clothes, especially in
pastel blues and greens, and they enjoy simple yet elegant jewelry.
Elves possess unearthly grace and fine features. Many humans and
members of other races find them hauntingly beautiful. An elf
achieves adulthood at about 110 years in age and can live to be over
700 years old.
Elves do not sleep, as members of the other common races do. Instead, an elf meditates in a deep trance for 4 hours a day. An elf resting in this fashion gains the same benefit that a human does from 8 hours of sleep. While meditating, an elf dreams, though these dreams are actually mental exercises that have become reflexive through years of practice. The Common word for an elf’s meditation is “trance,” as in “four hours of trance.”

Relations:
Elves consider humans rather unrefined, halflings a bit staid, gnomes somewhat trivial, and dwarves not at all fun. They look on half-elves with some degree of pity, and they regard halforcs with unrelenting suspicion. While haughty, elves are not particular the way halflings and dwarves can be, and they are generally pleasant and gracious even to those who fall short of elven standards (which, after all, consists of just about everybody who’s not an elf)

Elven Lands:
Elves mostly live in woodland clans of less than two hundred souls. Their well-hidden villages blend into the trees, doing little harm to the forest. They hunt game, gather food, and grow vegetables, their skill and magic allowing them to support themselves amply without the need for clearing and plowing land. Their contact with outsiders is usually limited, though some few elves make a good living trading finely worked elven clothes and crafts for the metals that elves have no interest in mining. Elves encountered in human lands are commonly wandering minstrels, favored artists, or sages. Human nobles compete for the services of elven instructors, who teach swordplay to their children.

Religion:
Above all others, elves worship Corellon Larethian, the Protector and Preserver of life. Elven myth holds that it was from his blood, shed in battles with Gruumsh, the god of the orcs, that the elves first arose. Corellon is a patron of magical study, arts, dance, and poetry, as well as a powerful warrior god.

Language:
Elves speak a fluid language of subtle intonations and intricate grammar. While Elven literature is rich and varied, it is the language’s songs and poems that are most famous. Many bards learn Elven so they can add Elven ballads to their repertoires. Others simply memorize Elven songs by sound. The Elven script, as flowing as the spoken word, also serves as the script for Sylvan, the language of dryads and pixies.

Names:
When an elf declares herself an adult, usually some time after achieving her hundredth birthday, she also selects a name. Those who knew her as a youngster may or may not continue to call her by her “child name,” and she may or may not care. An elf’s adult name is a unique creation, though it may reflect the names of those she admires or the names of others in her family. In addition, she bears her family name. Family names are combinations of regular Elven words, and some elves traveling among humans translate their names into Common while others use the Elven version. Male Names: Aramil, Aust, Enialis, Heian, Himo, Ivellios, Laucian, Quarion, Thamior, and Tharivol. Female Names: Anastrianna, Antinua, Drusilia, Felosial, Ielenia, Lia, Qillathe, Silaqui, Valanthe, and Xanaphia. Family Names: Amastacia (“Starflower”), Amakiir (“Gemflower”), Galanodel (“Moonwhisper”), Holimion (“Diamonddew”), Liadon (“Silverfrond”), Meliamne (“Oakenheel”), Naïlo (“Nightbreeze”), Siannodel (“Moonbrook”), Ilphukiir (“Gemblossom”), and Xiloscient (“Goldpetal”).

Adventurers: Elves take up adventuring out of wanderlust. Life among humans moves at a pace that elves dislike: regimented from day to day but changing from decade to decade. Elves among humans, therefore, find careers that allow them to wander freely and set their own pace. Elves also enjoy demonstrating their prowess with the sword and bow or gaining greater magical powers, and adventuring allows them to do so. Good elves may also be rebels or crusaders.

Elfin horoscope, "Casts" and affinity to Elements?

I already mentioned it in the now-closed thread, but I will ask again as there was no feedback back then. ;)

It could be that magical energy was so strong in the elves that they'd be born already bound/with affinities to a specific element (earth, water, air, fire). Just think of some kind of big horoscope which "naturally" defines what kind of jobs a person will be good at when they are adults. Not really a casts system, but more of a birth-right and a logical way to do things. What I mean is, if an elf would be born under XXX constellation/planet, these magnetic energies could give him or her (for example) a subtle understanding of nature and feeling for life-strenght (Earth) then he/she would most likely a healer. And so on...