Thanks for the link, pfranz...

From it:

Koko initiates the majority of conversations with her human companions and typically constructs statements averaging three to six words. Koko has a tested IQ of between 70 and 95 on a human scale, where 100 is considered "normal."

It would be very interesting to know how Koko would perform on a gorilla IQ test--to know whether she is an average gorilla or a genius gorilla. Suppose she were an average gorilla. Imagine how a genius gorilla would perform on the human, instead of my imaginary gorilla, IQ test.

'Course: It has been well-argued that human IQ tests finally only prove which people perform best on IQ tests and not much more.