Board Thread:Speculation House/@comment-173.200.7.205-20151206214731/@comment-144.13.83.96-20151211191844

What if it's genetic, and you get both your parents semblances at birth, but dormant, and the childhood events you experience sort of decide which actually manifest later on. The Schnees could then breed outside of their bloodline, but teach their children through their childhood in order to control the semblance and insure that the Schnee semblance manifested. Yang had a hard childhood, and took on her mother's semblance instead of her father's, while Ruby wanted to be like her mother, and so took on her mother's semblance through her training. We could then assume that, down Blake's bloodline, someone had the decoy semblance, and as a Faunus that was very useful, meaning that acted as the dominant semblance for many generations of her family, regardless of what other semblance options were there, until, like the rest, she manifested that semblance.

It's basically like any other gene, except the dominant/receiveness doesn't come about until the gene manifests. For example, lets (for the sake of the example) assume Weiss and Ruby had a kid. That kid, upon birth, would not have a semblance, as they activate for most during childhood (poor Jaune). Then, at a certain time, that child would unlock their semblance. If they were being taught by the Schnees, you could expect them to bring out the Glyph semblance through training. However, if the child was being taught to be a scyth-weilder by Ruby, you could expect the hightened agility and reaction speed of Ruby's semblance to be more useful, and that semblance would manifest instead.

I assume, like all genes semblances can mutate and change over generations, which is probably why we see so many different types of semblances nowadays.