There are equal arguments as to whether bending abilities are genetic.
- Katara's mother, father, grandmother, and brother cannot bend, but Katara can.
- In "The Fortuneteller", one of the twin brothers can bend while the other can't.
- Both of Piandao's parents were benders, but he is not.
- All people from the four nations learned how to bend– the technique hasn't always existed as a genetic ability.
- Genetic inheritance would explain why the benders of a certain nation don't have the ability to bend another element.
In an interview, Mike and Bryan said once that bending has to do both with genetics and spirituality, but never elaborated on it. So bending can be viewed as something like a talent.
It could be that the ability itself is inherited, but the bender who has inherited it can only develop their power to its true potential through the help of a master.
Perhaps all people must have at least one bender in their heritage. People, besides the Avatar, only have the ability to bend one element. For instance, in the poles, water is abundant; and as such, the human adaptation would be to control water. More so, with the Air Nomads, their choice to settle in a place of high altitude would mean an adaptation to control air.
The most important thing to consider as an argument either way is that the Air Nomad society consists entirely of airbenders. None of the other nations meets this case, and it seems that either their spirituality or genetics could be a factor in this.