The relation between social dominance and the menstrual cycle in female chimpanzees.

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Abstract
Response priority of chimpanzee mates in terms of a food-competition situation varied in apparent relation to the [female] menstrual cycle. This paper presents observations made regarding the same phenomenon in 5 pairs. 13 [female] were tested in 16 different pairings during various phases of the menstrual cycle. By means of a chute leading into their cages they were offered, daily, 10 pieces of food, one at a time at regular intervals. Response priority scores were obtained in terms of the number of pieces gotten by each animal in the daily session, and on the number of days each animal got any food. A total of 5190 trials were made. In all pairs one of the 2 subjects obtained food on the greater number of trials. This animal was designated as the "dominant." In 13 of the 16 pairs changes in response priority occurred. In 9 of these the subordinate animal obtained food more often when in the genital-swelling phase of her cycle, than in the permanent residual condition. Reliabilities on the various pairs were computed, and while significant in some cases, they were not in others. "Such a variety of behavior appeared in those pairs in which response priority varied in relation to sexual cycle that no single characterization of the psychobiological nature of relationship seems possible at present.".