Simmel also hypothesized between dyads and triads and how they may differ. Triads of wasps show more discrimination and aggression toward non-nestmates than dyads of wasps. Medieval and Renaissance cadences are based upon dyads rather than chords. All members have six eyes arranged in three groups of two (dyads). Sessions are in groups with no more than 6 parent-child dyads. These dyads are elements of psychological structure. HLM also allows for analysis of growth curve models of dyads and groups. Georg Simmel wrote about dyads, or partnerships with two people. Individual tones, octave dyads, and major chords are quite high in tonalness. Third, animal models are commonly utilized in studies of co-regulation within adult dyads. Plutchik also theorized twenty-four "Primary", "Secondary", and "Tertiary" dyads (feelings composed of two emotions). In turn, this led to being able to play dyads and chords. Sisters are most likely to maintain contact with one another, followed by mixed-gender dyads. Female-female dyads groom far more than male-female and male-male dyads. Democratic dyads have a 55% reduced chance.