As in humans are 'designed' to live in communities/tribes and nowadays a lot of us live very solitary lives, getting a large portion of our input from the internet or the telly. I guess this is also why mumsnet does so well, our own cyber community.
I reckon the lack of social interaction (and generally just being around others and extended family) is responsible for the rise in depression and anxiety, especially affecting people when they need their tribe the most, i.e. post natal women and the elderly.
Is this an unreasonable conclusion and if not what can people do to minimise the isolation apart from joining a commune?