There was a wonderful episode of Nova, called "The Secret of the Wild Child." It was about "Genie" a girl who was kept in isolation until she was found at 13. She couldn't talk. Scientists, though drawn to her, also saw an opportunity to test nature vs. nurture. It is a wonderful show, but everything was inconclusive because they could not determine whether Genie was born mentally retarded, or is her retardation was a result of her total isolation. There are very few cases of total isolation, so balance of nature vs nurture is hard to discern. I do believe, like some of you, that it's a combination.
It's a mesmerizing story. The girl draws you in. I wonder what ever happened to her.
Transcript
here.