When I said isolated I meant it in exactly that fashion. Isolated and withdrawn, but close enough to still fall back into society if the need - due to internal or external reasons - arose. Someone removing themselves from even the remote chance of human interaction is unlikely to have any evolutionary advantage. And unless I'm reading the article wrong, he did eventually rejoin the masses after 27 years.

I guess was talking about people who feel the need to withdraw in general. I think we've all met a person or two like this, who prefered to be alone. Some just take it further than others.