The correct answer is the group of Romanian orphans adopted by Western families. Harry Harlow is an American psychologist known for his highly controversial experiments on the maternal and social isolation in Rhesus monkeys. These experiments along with several previously developed theories formed the attachment theory. Harlow's experiments showed that monkeys isolated from their mothers at birth, exhibited later on in life aggressive behaviour and were unable to form social relationships. These experiments suggested that maternal separation can lead to animals with antisocial behaviour. At the end of the Ceausescu regime in Romania, a big number of orphans were adopted in Western families. These orphans experienced poor living conditions in Romanian institutions, with no social interaction or proper nutrition. Romanian and British scientists followed the progress of these adopted orphans and the results suggested that this early deprivation was the cause of some social deficits. However, scientists are optimistic that these deficits can be reversed in some cases.
