Another proposed adaptive function is creating intra-group bonding. In this aspect it has been seen as complementary to language by creating strong positive emotions while not having a specific message people may disagree on. Music's ability to cause entrainment (synchronization of behavior of different organisms by a regular beat) has also been pointed out. A different explanation is that signaling fitness and creativity by the producer or performer in order to attract mates. Still another is that music may have developed from human mother-infant auditory interactions (motherese) since humans have a very long period of infant and child development, infants can perceive musical features, and some infant-mother auditory interaction have resemblances to music.