Cyclic changes in hormonal, physical, behavioral, and linguistic measures in a female lowland gorilla

Since 1972, Koko, a captive-born female lowland gorilla, has been the subject of longitudinal linguistic and behavioral research. Data on behavioral and physical concomitants of Koko's estrous cycle have been gathered since her cycles began at the age of 5 years, 9 months. This study presents evidence of endocrinological influence on cognitive functioning: It demonstrates that frequency of sign-language use by Koko is greater in the follicular phase of her reproductive cycle. This finding supports an earlier report on Koko and is in agreement with recent studies correlating human menstrual-cycle phases with patterns of manual sequencing and verbal fluency. This study also confirms that nonlaboratory hormone tests designed for human female urine samples appear to be useful for detecting luteinizing hormone (LH) in gorilla urine and establishes the applicability of such tests for determining pregnanediol-3-glucuronide (PdG) levels in gorilla urine. Analyses of preliminary test results indicate that these enzyme immunoassay (EIA) tests match earlier radioimmunoassay (RIA) findings on the relationship between reproductive hormones and variables such as genital swelling and proceptivity in female gorillas.