Renne

Renne definitely knows about magical ability running in bloodlines, and through creatures - the Tarutaru themselves have natural resistance to magic, and even the dullest of their numbers can feel other magic in the air. She's read a few papers on affinities for particular types of magic running through families, and one pointing out that Viera would have severe back problems from their fondness for high heels were it not for a curious blessing among their kind.

As for Materia growth, the current widespread theory on Materia is that it's a fungus-like mineral that grows when exposed to magic for extend periods of time. It reproduces through absorbing enough magic that it grows and creates another, lesser form of itself, but Materia "spores" are sometimes found and, with enough magic, start to form proper Materia.