Koko nearly died as an infant at the San Francisco Zoo. She became very sick and needed round the clock care to nurse her back to health. Koko eventually recovered and was living in the nursery at the San Francisco Zoo when she began participating in a language study with Penny Patterson, a student at Stanford working toward her Ph.D. at the time.
Penny would spend time with Koko every day. In the mornings, before the zoo opened to the public, Penny and other caregivers would take Koko out on walks around the grounds. This provided plenty of opportunities for communication. Koko was immersed in spoken English and American Sign Language (ASL) from an early age and had Penny as a lifelong, consistent caregiver.