Koko, a gorilla said to have mastered American Sign Language, died in the US state of California at the age of 46 on June 19, 2018. Born at the San Francisco Zoo in 1971, Koko was said to have an IQ of between 75 and 95. The average IQ for humans is 100. Koko used 1000 words of sign language to communicate with humans and understood 2,000 words of spoken English. The gorilla also gained public attention for caring for cats.