Taking care of the young as a joint activity
Once the intentional communication and cooperation between the mother and the infant are established in a social group, all individuals go through this phase as infants and all female individuals experience it from the maternal side.
Since the mothers, as has been observed in various cases, would otherwise be overwhelmed with the task of raising the children alone, fathers, grandmothers, older siblings and other relatives also take on the responsibility of looking after and caring for the offspring.
These individuals will also use the new intentional communication they have experienced and which the infant demands from them when they communicate with the infant.
Since the new form of communication does provide advantages, adolescents and then later adults will playfully make use of intentional communication and cooperation. This is how the new form of communication will become established in the social group.