Bowlby developed a theory which focused on the idea that the continual presence of care from a mother or mother substitute is essential for normal psychological development of babies and toddlers, emotionally and intellectually. Bowlby said that mother love in infancy and childhood is as important for mental health as are vitamins and proteins for physical health. Being separated from a mother in early childhood has serious consequences.
Separation vs deprivation
Separation means the child isn't in the presence of the PAG. This only becomes a problem if the child becomes deprived of emotional care (this can happen even it the mother is present). Brief separations, when the child is with a suitable substitute who can provide emotional care, aren't significant for development at extended separations can lead to deprivation (which by definition, causes harm).
Critical period
Bowlby saw the first 2-5 years of live as a critical period for psychological development. If a child is separated from their mother in the absence of suitable substitute care and so deprived of emotional care for an extended duration during this critical period then psychological damage was inevitable. He also believed there was a continuing risk till the age of 5.
Effects on development - Intellectual
Bowlby believed that if children were deprived of maternal care for too long during the critical period they would experience delayed intellectual development - abnormally low IQ. This has been demonstrated in studies of adoption. Goldfarb found lower IQ in children who had remained in institutions as opposed to those who were fostered & thus had a higher standard of emotional care.
Effects on Development - Emotional
Bowlby identified affectionless psychopathy as the inability to experience guilt or strong emotion towards others. This prevents a person developing normal relationships and is associated with criminality. Affectionless psychopaths can't appreciate the feelings of victims so lack remorse for their actions.
Bowlby's 44 thieves study examined the link between affectionless psycopathy & maternal deprivation. The sample in this study consisted of 44 criminal teenagers accused of stealing. All thieves were interviewed for signs of affectionless psychopathy : characterised as a lack of affection, lack of guilt about their actions & lack of empathy for their victims. Their family was also interviewed in order to establish whether the thieves had prolonged early separations from their mothers. The sample was compared to a control group of 11 noncriminal emotionally disturbed young people.
Bowlby found that 14/44 thieves could be described as affectionless psychopaths ; 12 of these had experienced prolonged separation from their mothers in their first two years. In contrast, only 5 in the remaining 30 thieves had experienced separations. Only two participants in the control group of 44 had experienced long separations. Bowlby concluded that prolonged early separation /deprivation caused affectionless psychopathy.