Talk:Bumi/@comment-76.113.18.134-20120619041253/@comment-5143091-20120619124630

Bending is primarily genetic, with some spiritual tampering when it comes to the Avatar. Certain genetic traits allow one person to bend a certain element, while another set of traits allows someone to bend a different element, or not bend at all. depending on what genes are available from the parents, there are multiple combinations for being a bender of one type or another, or being a non-bender. We know Katara has nonbending genes because Sokka and her parents are all nonbenders. Aang's lineage is unknown but we know he is Air Dominant, while Katara is Water Dominant. Since we can safely assume neither have any Fire Nation or Earth Kingdom genes, the potential possiblities for their children would be Airbender, Waterbender, or Nonbender. While it was a rare possibility in Aang and Katara's case, there was a chance for them to have an non-bending child. Which they did

http://www.youtube.com/watch?v=Yji6Hn315PY

http://www.youtube.com/watch?v=XsVdZgyivpA&feature=relmfu

Check these out. they explain it much better