This is a fascinating topic! I'm not sure if you are familiar with the story behind the modern "wild-child" known as "Genie." It's not her real name, as it was given to her to protect her identity.
"Genie" was discovered at the age of 13 in 1970. Her deranged father had locked her in a room alone for over 10 years. She spent most of this time tied down to a chair, and slept in an oversized crib, covered by a metal screen- only when her family didn't forget to untie her at night!
During this time of intense neglect and abuse, Genie was not exposed to language. Her father did not speak to her and instructed other family members to also not talk to her. As such, she had acquired very little language- limited to phrases such as "no more" or "stop".
When her mother (who was afraid of the abusive father) finally got Genie and her other child away from the home, Genie was 13 years old and only weighed 59 lbs! The social workers initially thought she was 7 years old and autistic.
Interestingly, Genie began to learn to speak through therapy. While at first her speech recovery seemed rapid, she hit a developmental ceiling. She acquired some basic language skills, and would string together basic phrases such as "no have food". However, her language skills never developed beyond this- She was never able to say it properly ("I do not have food"), and the number of words in her vocabulary never developed beyond a few hundred.
Now, the questions are, of course, why did this happen? Some language theorists say that language must be learned in a "critical period"- typically before the teenage years (adolescence). This makes for an interesting combination of the idea of nature vs. nurture. Some scientists claimed Genie's condition is proof of this. Some of the scientists studying Genie disagreed, saying that her level of abuse and neglect contributed to her lack of vocabulary. Others pointed out that she did not have any left hemispheric activity in her brain, which inhibited her ability to speak properly.
Perhaps it is a combination of all of these things? It is difficult to say. I've written too much! :) What do you think?
(and btw, I'm not sure that I will talk about feral children directly. i will talk about many of the related issues from above tomorrow, as well when we discuss language and development.)
-jwn