The US administration's "zero tolerance" policy that led to more than 2,300 children being separated from their families in the first month of its implementation sparked widespread condemnation and outrage.
The Trump administration was forced to back down on this policy, signing an executive order that would ostensibly halt the practice of separating families at the border.
The executive order, however, did nothing to undo the damage already done nor reunite the thousands of children still forcibly separated from their parents.
One of the cruellest and most damaging things we can do to children is to deprive them of their primary caregivers. We know this intuitively and we know it from the tears and fears expressed by young children at the prospect of being separated from their loved ones.
Even relatively minor separations, like the first day at nursery, can be fairly traumatising for pre-schoolers and parents alike.
Alongside our intuition and common sense, decades of research have demonstrated the ill effects of depriving children of their parents or primary caregivers.
The hugely influential psychologist, child psychiatrist and psychoanalyst John Bowlby devoted his career to exploring the consequences of what he termed "maternal deprivation".
Writing in the 1950s, Bowlby concluded that “mother-love in infancy is as important for mental health as are vitamins and proteins for physical health”.
Bowlby studied children who had been separated from their families, cataloguing a host of problems he attributed to their experience of disrupted attachment.
These included physical consequences such as stunted growth (known as psychosocial short stature, or PSS) through to a whole spectrum of social, emotional and behavioural problems too.
Even relatively brief separations in early infancy were viewed as having physical and psychological consequences that might persist into adulthood.
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One of Bowlby’s collaborators, the celebrated developmental psychologist Mary Ainsworth, took this work further.
Beyond case studies, Ainsworth went on to explore infant attachment styles in a laboratory setting. To do this, she established a procedure that became known as the “strange situation”.
The process involved briefly separating an infant from its primary caregiver (usually the mother) while a psychologist would surreptitiously observe the infant’s response to separation and reunion from behind a two-way mirror. The infant’s reactions were coded and catalogued as "attachment styles".
Ainsworth discovered that healthy, "secure" attachment styles in infants were associated with a consistency of care provided by the primary caregiver. Prolonged separation between infants and primary caregivers could lead to inconsistent care and therefore the development of "insecure" attachment styles or even attachment disorders.
Taking on the theories of Bowlby and Ainsworth, other psychologists have looked at how the links between attachment styles and relationships play out in adulthood.
While not set in stone, insecurely attached children tend to grow up to have insecure attachment styles in adulthood.
The opposite is true for securely attached infants, who tend to grow into adults who enjoy secure relationships, feel good about themselves and others and are compassionate and self-confident.
Secure attachment styles are associated with better coping methods and resilience across a range of stressful and adverse life events, from personal failures to relationship breakdowns and chronic pain.
Conversely, insecure attachment styles are associated with increased vulnerability and distress and are viewed as a trans-diagnostic risk factor for numerous psychological problems.
In short, we know that separating children from their families can have devastating and enduring implications for the individual, for their future relationships and for society as a whole.
We are aware that separating, or even threatening to separate, children from their loved ones provokes enormous amounts of anxiety and distress.
We know that when we deprive children of their caregivers, they might cry themselves to sleep, regress into bed-wetting and might even stop growing for a while as a result of PSS. We know all of this and have known it empirically for at least 50 years, so how could such a policy have been proposed and passed in the first place?
The reversal of the so-called zero-tolerance policy is great news. Greater news, however, would be assurances that the thousands of children separated from their families between April and June of this year will not suffer any lasting psychological consequences as a result of their inhumane ordeal.
Unfortunately, such assurances are not possible and all the children separated are not yet reunited with their parents.
One Honduran man, Marco Antonio Munoz, separated from his wife and three-year-old son at the US-Mexico border, reportedly took his own life inside a Texas jail last month. That is at least one family that, tragically, will never be fully reunited and a consequence that must never be repeated.
Dr Justin Thomas is professor of psychology at Zayed University and author of Psychological Well-Being in the Gulf States
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