Board Thread:Questions and Answers/@comment-25801533-20150531094407/@comment-10452902-20150603215503

Actually, that doesn't make sense. Plus in the Soul Society can reproduce otherwise it would be impossible for the noble families to maintain their numbers and strength, let alone produce someone who can use a Bankai

From what I understand, they can reproduce which would how noble families are able to maintain their power and produce a captain. It also makes sense since most member of the noble families would never die easily but live for hundreds of years therefore, their numbers would be far too small if they could only increase in size through reproduction in the World of the Living. We don't really have all the fact so it's difficult to say for certain so most of this is speculation at best.