Genie's case does in some way prove that there is a critical period for language development. As it's usually the case with feral children who become integrated in society once again, in most cases the sooner they are exposed to human contact the faster they learn the language - albeit it's a rarity for a feral child to learn how to speak.
It's related to the muscular structure of the vocal organs, their potential must be trained from the earliest age otherwise it's not uncommon for them to lose their function.
As for the "nature versus nurture" aspect, there are a lot of things to consider in this peculiar case. First off, that the child suffered extreme psychological trauma, from the constant abuse to crippling absence of external stimuli
It's related to the muscular structure of the vocal organs, their potential must be trained from the earliest age otherwise it's not uncommon for them to lose their function.
As for the "nature versus nurture" aspect, there are a lot of things to consider in this peculiar case. First off, that the child suffered extreme psychological trauma, from the constant abuse to crippling absence of external stimuli