Some people may be genetically prone to be lonely, a study suggests.
Being socially isolated leads to an early grave and is considered to be as damaging as smoking 15 cigarettes a day.
And new research on rhesus macaques – who congregate in groups of up to 200 – revealed some monkeys choose to be lonely for most of their lives.
A team of international scientists believe this suggests their isolation is caused by a persistent trait or traits that they are unable to control.
Researchers from the universities of Exeter, Puerto Rico and Pennsylvania claimed the cause is a mixture of their genes.