Can social isolation kill babies? According to the Wikipedia page for Language Deprivation Experiments, > An experiment allegedly carried out by Holy Roman Emperor Frederick II in the 13th century saw young infants raised without human interaction in an attempt to determine if there was a natural language [...] > > The experiments were recorded by the monk Salimbene di Adam in his Chronicles, who wrote that Frederick encouraged "foster-mothers and nurses to suckle and bathe and wash the children, but in no ways to prattle or speak with them; [...] But he laboured in vain, for _the children could not live_ without clappings of the hands, and gestures, and gladness of countenance, and blandishments." There are many feral children that survived without social interaction, but I couldn't find any result for children that died from social isolation and not because of abuse. Can social isolation kill babies?

We cannot be sure exactly what happened 7 centuries ago; we only have the one account. However something akin to this experiment did occur, albeit without the controlled conditions. In Romania during Communism thousands of children were consigned to orphanages where they were grossly neglected (warning: the linked article contains distressing details).

Many children died under this regime, but we can't tell how much was due to physical versus psychological factors. However many survived despite the neglect.

This article in the Guardian reports that the children have specific areas of the brain smaller than children with normal upbringing.

In conclusion, it seems that gross psychological neglect has measurable neurological consequences but is not generally fatal, contrary to the report of Salimbene di Adam.