I mention in Wed.'s post that the human race has been lonely (i.e., so many of us feel isolated so often, and so deeply) for too few centuries to allow evolution to help us adjust/adapt. So we must either suffer or use cultural compensations. (The latter may work well, such as when we pursue spiritual exercises, or fail miserably, such as when we turn to addictions to shopping, drinking, and technology to "fill the hole that cannot be filled.")
Why is evolution so darn slow?
Genetic mutations are typically accidental and infrequent, for one thing. And any that just happen to be good require the organism to gain a reproductive advantage by having them. So if you are the first person born with the ability to go on long treks alone without going mad and hallucinating companions (humans or gods), then that's great for you if you have to risk your life on such treks, then you survive to marry a hot chick and have lots of healthy babies. (Evolutionary biologists do lots of sexy thought experiments like this.)
Since young people die of all sorts of things before they mature, there is no way of knowing how many fabulous mutations have arisen over the millennia, only to die with them. (And many adults with good traits have failed to have children, as well - same difference.)
Physically crucial traits, such as the ability to feel pain or hunger, are very strongly selected for: people who cannot feel their bodies' needs to avoid injury or seek food die pretty young. But psychological problems can be overridden. (Which may partially explain why genes for depression have not been weeded out over time.)
Pangs of loneliness have been as useful to us (as social animals) as hunger pangs. But the fast-paced modern world has, perversely, made food more available to appease hunger, and made companionship less available. We have adapted neither to seeing too much yummy, affordable food everywhere, nor to seeing too few friendly faces around us. The results are epidemics of obesity and loneliness.
While many of us nostalgically recall earlier times (say, 100 years ago), where everyone knew everyone else in town, and people had lifelong relationships, I doubt anyone would want to have the food scarcities and food poisoning of the same era. Modernity has given with one hand (greater physical sustenance) while taken away with the other (fewer strong communities and interpersonal relationships).