Er, now I'm really confused! So...you think that people CAN learn how to bend without the help of the lion turtles? I guess, I always just assumed that, Lion Turtles gave them the bending ability, and then only after that, those that had bending from them, were able to pass it on with genetics.
I never though that, bending was something anyone could achieve. Or that there was bending in genetics prior to the Lion Turtles. lol Then again, the whole thing is kind of confusing to me. The fact that Bison are the original air benders, wat. So like, I guess Turtles are animals....so I guess that kind of makes sense? That animals had bending before humans, or something.
*head explodes*
You assumed it, but nothing of the sort was ever stated. In the World of Avatar, some people can bend while others can't, and that has never changed throughout ATLA and LOK. Genetics, spirituality or pure luck, it's always been the same mixed of muddled reasons why humans can bend.
Some people simply had it. You're not the first one to be confused by this since, from what I've been reading online, a lot of people forgot this very essential piece of information from ATLA, despite that it was talked about a lot in many episodes (the guys at the Republic City Dispatch podcast, for example, were surprised the Sky Bison were the original airbenders after watching Book 3 of Korra, what?!)
The original benders, physical beings that could manipulate the four elements, were sky bison, badgermoles, dragons and, in the case of waterbending, the Moon and Ocean (which were spirits). This is essential to the mythology of ATLA. The Lionturtles, physical animals and NOT spirits, had the ability to energybend.
In LOK, this is expanded upon: In the era before the Avatar (the era of Raava, as it's called in the Avatar Wiki), the Lionturtles energybent humans so that the ability to bend an element was awoken within them (and then, removed).
Also, the bending animals do not "give" bending to humans, simply that some humans began to look to them and think "hey, could we do that?" and viola,
some discovered that they could and learned fire bending from the Dragons, others pushed and pulled like the tides (moon and ocean), airbenders started whooshing around air like the sky bison, and others (like Toph) copied the movements of badgermoles.
LOK did not retcon this. We could infer that what the Lionturtles regularly did to humans had a lasting effect, or maybe it was the creation of the Avatar coupled with Harmonic Convergence that awoke bending in some humans. Wether or not these humans already had the ability to bend before, is not stated.