Koko is a female western lowland gorilla

Western Lowland Gorilla

The western lowland gorilla is a subspecies of the western gorilla that lives in montane, primary, and secondary forests and lowland swamps in Angola, Cameroon, Central African Republic, Congo, Democratic Republic of the Congo, Equatorial Guinea and Gabon. It is the gorilla usually found in zoos...

 who, according to Francine "Penny" Patterson

Francine Patterson

Dr. "Penny" Patterson is an American researcher who taught a modified form of American Sign Language, which she calls "Gorilla Sign Language", or GSL, to a gorilla named Koko....

, is able to understand more than 1,000 signs based on American Sign Language

American Sign Language

American Sign Language, or ASL, for a time also called Ameslan, is the dominant sign language of Deaf Americans, including deaf communities in the United States, in the English-speaking parts of Canada, and in some regions of Mexico...

, and understand approximately 2,000 words of spoken English.

As with other ape language experiments, the degree to which Koko masters these signs has been controversial, as has been the degree to which such mastery demonstrates language abilities.

Koko was born at San Francisco Zoo

San Francisco Zoo

The San Francisco Zoo, housing more than 260 animal species, is a zoo located in the southwestern corner of San Francisco, California, between Lake Merced and the Pacific Ocean along the Great Highway...

 and has lived most of her life in Woodside, California

Woodside, California

Woodside is a small incorporated town in San Mateo County, California, United States, on the San Francisco Peninsula. It uses a council-manager system of government. The U.S. Census estimated the population of the town to be 5,287 in 2010....

, although a move to a sanctuary on Maui, Hawaii, has been planned since the 1990s.