Attachment is believed to be an innate, evolutionarily adaptive tendency to form bonds with caregivers (e.g., Hodges et al., 2003; Lewis, 1990). Differences in attachment relationships suggest that it emerges from a process which is biologically driven, but the nuances of the relationship are shaped by events occurring in real life. Attachment relationships are thought to be necessary in infancy to set the course of future relationships with other people. Insecure attachment in early life predicts later problems, including aggression (Loeber & Hay, 1997). Research has shown significant continuity of attachment categorizations as secure or avoidant, for example, across childhood (e.g., Ammaniti, Speranza, & Fedele, 2005), but modest ones from early childhood to adolescence and adulthood. Evidence is limited on the ability of early attachment classifications to predict later aggressive and disruptive behavior (Pettit, 1997), but because of the centrality of child attachment behavior and parental sensitivity in infancy, disturbed interactions during infancy are expected to have a potent effect on future interpersonal problems.
Relating to our discussion of sensitive periods, the attachment process must begin very early in life for the normal process to occur (Lewis, 1990). Attachment- related behaviors such as stranger anxiety and separation anxiety emerge about the same age in all human societies and in chimpanzees about that age too, “suggesting a long evolutionary history” (Geary & Bjorklund, 2000, p. 59). Evolutionary psychologists hypothesize that attachment behaviors were selected due to the reduction in infant mortality.
Some babies, such as preterm babies and those with mothers who have psychological problems such as depression, are more likely than others to have disturbed interactions (Field, 2007). Associations between depression in mothers and problems in babies, such as cognitive deficits, are thought to be due, in part, to impaired interactions.
Poignant examples have been provided in the literature in studies of children from Romanian and Bosnian orphanages where food and shelter were provided, but the babies were not given attention or cuddling (e.g., Miller, Chan, Tirella, & Perrin, 2009; Rutter, Kreppner, & O’Connor, 2001; for more on severe deprivation, see Smith et al., 2003).
Orphan studies have shown that children who are not provided “mothering” in the form of handling, rocking, and affection suffer from many adverse outcomes, even compared to other infants living in nurseries. Behaviorally, they have been observed to show retardation of motor behavior, delays in head control and walking, little interest in the environment, crying rather than trying to escape from unpleasant stimuli, deficits in emotional reactivity, and failure to seek an adult when in distress. While no comparison to a group of children exposed to such deprivation at other periods in life has ever been provided, we might expect that it would not have the same effects among older children. Long-term follow-up of children placed in homes has found that institutionalized infants remain deficient in language and social relations when followed up to ages 10-14 (Provence & Lipton, 1962). They were noted to be aggressive and “unrepentant” as well.
In animal studies, significant distress is found in maternally-deprived baby monkeys and some other animals (Gandelman, 1992). Early films of experiments involving maternally-deprived primates provide a sad example of these effects (e.g., Harlow, 1958; Harlow & Suomi, 1971). They have been observed to experience physical “wasting,” including lack of appetite, pallor, loss of muscle tone, vomiting, diarrhea, and excessive sleep as well as “exceptionally high” (p. 129) mortality rates (Gandelman, 1992). Isolated monkeys later have trouble in peer relationships (associated with delinquency in humans) and do not initiate or reciprocate grooming or play with peers. Other behavioral symptoms such as sterotyped rocking and self-clutching are present. Dogs are adversely affected by maternal and littermate privation. They become nonvocal, nonoral, and later have problems with aggression. Prolonged individual housing creates “social deprivation syndrome” or “isolation syndrome” in some species (Gendreau & Lewis, 2005). Isolated animals exhibit high levels of emotional reactivity to various stimuli. They are hyperreactive even to mild, nonthreatening stimuli, especially social stimuli. Social deprivation has been associated with aggressiveness, social avoidance, depression, and defensive/fearlike behavior in primates, dogs, and rodents. Socially deprived animals also demonstrate learning deficits and inadequate reproductive and maternal behavior including neglect and abuse that sometimes results in death their own infants (Gandelman, 1992).
Thus, although empirical reviews have not emphasized caregiver sensitivity, or attachment, as an important cause of violence per se, we have selected it as a good prospect in our search for likely causes.