I was reading about apes learning sign language, and I saw that Koko the gorilla began learning sign language at the age of 1,and by the end of her life could sign 2,000 words. I had been wondering why great apes, who allegedly have an IQ comparable to a slow human child, never develop many of the abilities and skills that come so naturally to humans, mainly abstract thought.

I remember a case where a girl was discovered having been badly abused, spending her entire life chained to a high chair, where she was fed once a day and never really spoken to. There was also never anything in her room to stimulate her mind, and she was often left in complete darkness. She was rescued around 12 years old, but they had trouble determining her age because she had been so neglected and malnourished.

Even though she was taken in by a child psychologist for a year, and worked with an expert in communication, especially in abused children, the girl was never able to learn language. She was able to learn words comparable to Koko, but she was never able to learn grammar or abstract concepts.

It is believed, and Chomsky developed a lot of this, that the human brain is programmed to naturally develop language between the ages of 1 year and 4-5 years. By age 5, the brain has developed concepts like theory of mind so that side by side with language, the child has gained the ability to accurately describe and think about their experiences, as well as imagining.

Does the fact that other apes can only learn words and not language prove that they lack the ability to learn language? That it is more than just an issue with them being unable to speak?If so, how was the leap made from no ability to language learning being programmed in?Does this point to there being something special about our intelligence that makes it incomparable to other animals?Or is language so important to abstract thought that it alone gives us such an advantage.