You've never seen a firebender born to a family of waterbenders, have you? I think its a mix.

It has to be genetic and spiritual both. The fiery whackos of the earth kingdom cant bend fire, so it cant be entirely spiritual. And those who do bend in the Earth kingdom only bend Earth, so its gotta be genetic/spiritual.

BTW you said its kind of spiritual, then its also spiritual. Silly goose.

Well, (and I can't believe I'm saying this) Joychi made a good point. *flinches and waits for the world's end*
Genetic in a sense of who your original decendants are--and if a male firebender were to have a child with a female waterbender, the child would most likely be a firebender(if a bender at all), due to the fact that it is an Asian culture, and the legacy is carried on through the males. The spirits watch over their specific nation; that's why there were so many waterbenders in the Northern Tribe, but only one in the Southern. Since the spirits had taken a physical form, they couldn't really make the journey, so perhaps Katara was also a bender in her past life? Meh, just throwin' around ideas, here.

That's what I've been sayin'!!!!!!!!!!

The child's bending is going to be the same as his ancestors if at all(genetic)

And he'll only be a bender if his spirit matches the spirit of the bending itself(spiritual)

A MIX I SAY!

Have you ever seen a guy who had his two parents bending differents elements ? Then we could tell it. Because we don't have any exemple, Tyro was married to a non bender and Haru was an Earthbender, it's the same thing for Zuko but it's just for the boys.

Close, but not quite, Joychi. Yes, I said the ability is passed through the males, but I'm not saying that Haru would HAVE to be a bender due to his father. Just cross-element....
OK, OK, genetic too. Rub it in my face, then, Kemari. ;_;

I agree completely with Kemari, its a mix. You could say that there are dominant and recesive traits, but the spirits ultimately decide who is a bender. Its just more likely if you have a bender close to you in the family. Thats my opinion. Anyway, I did this mainly because I wanted 100 posts because Arashiko is totally pwning me in postage.

What Kemari said doesn't prove anything because it's obvious that a child bending will be the same as his ancestor since they're from the same Nation and this is why it's spiritual because you can only bend your nation's element. I know what you're gonna say, if a bender has his descandants in another nation they'll still have the same bending as their ancestor so that's genetic too. WRONG because the ancestor is from a certain nation so the spirituality will make that his descendants will have the same bending as him. So it's more spiritual than genetic. *applause, "thanks, thanks a lot"* (I tried to translate in english as well as I could so I hope you'll understand ;D)

I think of it like this. Bending is based on spiritual energy, but you can't tune into said spiritual energy if you don't have the right biological hardware gifted to you by your ancestors... Each nation has a patron spirit of some kind, and I gather that they are fairly territorial with their 'human breeding stock', so that crossbreeds favor one side of their heritage or are scorned by both patrons as 'tainted', the Avatar representing a ancient pact of balance between the four signed 'somewhere near the begining'

Did you really understand what Halaku said, Arashiko ? I think my theory is more plausible than his. Because his idea about these "spiritual patrons" is hard to understand.

In the Cave of the Two Lovers, their patron spirits for the earthbenders were the mole thingies. I have to agree with Halaku on this one. I mean, what he said makes sense. If an Earthbender and Waterbender were to have a child, there would be a 75% chance for one, and a 25% for the other depending who was male or female. If they turned out to be an Earthbender, tehy would have to whorship the moles. Besides, the Swamp Waterbenders are members of the Earth Kingdom, so that discounts that they have to bend their Nation's element.

Look. Way back in the finallie to season one, it was explained that 'Tui and La crossed over to become one with the world'. Subsequently, when one of them keeled over, all the Waterbenders lost their powers. By extrapolation, all of the nations have to have patron Bending spirits in one way shape or form, likely some sort of imortal animal.

The Water Tribe gets fish. The Earth Kingdom could have a Badgermole. The Fire Nation has who knows what. And the Air Nomads? Maybe they had a lemur.

Anyway, each of these patrons channel their respective power to their followers, provided they have the right hardware, of course...

You're saying its not genetic because they have the spirituality of their nation. If your ancestor is an earthbender, and you have the spirit of an earthbender, and all your other relative bend water, you'll likely be an earthbender. It's a genetic spiritual mix. No dur if your ancestors are earthbenders and you have the spirit of an earthbender youll be an earthbender! What your saying is, its not because theyre genetic, its because they're like their nation, at least spiritually. Well, if their family was of the nation, and they werent related to a bender at all, would they be able to bend? That's the big question to determine if its spiritual or genetic: If their family cant bend, can they be able to at all? I dont think so.

That was uncalled for Kermari. The fact that we are limit in knowledge means that any of our theories could be true. If you disagree with someone, then disprove their idea in a logical fashion with what facts you have.

I a have an alternative theory that could be argued as ether genetic or spiritual. If you have two benders of different element try and breed, you would get no benders at all. Genetically this could be seen as the genes in conflict with each other and just cancel out (my knowledge of genetics is a little weak though). Or the sprits could have agreed on a stop gap in an effort to maintain balance.

I do agree that bending is passed on through a person's heritage. It would explain how the swamp dwellers are earth kingdom citizens and waterbenders. Perhaps they were very old off shots of the water tribes, maybe an exploration team. Because of the isolation of the swamp, they were able to prevent mixed breeding.

Fair enough, Do Sho. Post modded.

One thing about your post however: I do not think genes 'cancel out'. You either have dominant or regressive, and every gene for a trait falls into a category. for example, here's what eyes look like, from most dominant to most regressive:

Brown
Black
Hazel
Blue
Green
Grey
Red(albino)

Thats just basically. Thers more colors(pale icy blue, green-blue, etc) but that's how genes work in a nutshell. If you have a gene for grey and for green, you'll have green, always.

Following this, I think that either, 1) Some bending genes are more dominant than others, thus always creating one type of bending over the others in the case of mixed families.

or, 2) Bending is only genetic in the sense that the spirits bless the descendents of the first benders with bending, which I think is the case,

or finally, 3) Bending genetics do not follow any dominant/recessive trend like most genes

These are my thoughts

Yes I would go with #3. But like I said be for, my knowledge of gentics is not that great to determine if that is even possible.

When you're talking about the eyes' colors, you're talking about the Avatar's world or in the real world ? Because I'm a bit lost, I don't see the relationship with the bending. And the bending didn't come from the genes, it came from the spirits. It may be transmissible by genetic because if a Waterbender and an Earthbender had a child, here is how I think things would work :
There would be:- 25% of chance that he would be an Earthbender
- 25% of chance that he would be a Waterbender
- 50% of chance that he wouldn't bend at all
But if that child had a baby, the bending of his baby would depend on the bending of the mother. If she was a Waterbender, the baby would be a Waterbender, and if she was an Earthbender the baby would be an Earthbender because of the genes of the father. I don't know for Firebending. I proved that the bending was possibly transmissible by the genes but it came from spirits. So now I recognize my error : it's a mix (I can't believe I admitted it).