 Montagu said that the retention of these juvenile characteristics of the skull into adulthood by australopithecine or Homo Erectus could have been a way that a modern type of human could have evolved earlier than what actually happened in human evolution.The psychiatrist Stanley Greenspan and Stuart G. Shanker proposed a theory in "The First Idea" of psychological development in which neoteny is seen as crucial for the "development of species-typical capacities" that depend upon a long period of attachment to caregivers for the opportunities to engage in and develop their capacity for emotional communication.Because of the importance of facial expression in the process of interactive signaling, neotenous features, such as hair loss, allow for more efficient and rapid communication of socially important messages that are based on facially expressive emotional signaling.