No wonder we're so smart...

City life hurts your brain. 

Now scientists have begun to examine how the city affects the brain, and the results are chastening. Just being in an urban environment, they have found, impairs our basic mental processes. After spending a few minutes on a crowded city street, the brain is less able to hold things in memory, and suffers from reduced self-control. While it's long been recognized that city life is exhausting -- that's why Picasso left Paris -- this new research suggests that cities actually dull our thinking, sometimes dramatically so.
"The mind is a limited machine,"says Marc Berman, a psychologist at the University of Michigan and lead author of a new study that measured the cognitive deficits caused by a short urban walk. "And we're beginning to understand the different ways that a city can exceed those limitations."
One of the main forces at work is a stark lack of nature, which is surprisingly beneficial for the brain. Studies have demonstrated, for instance, that hospital patients recover more quickly when they can see trees from their windows, and that women living in public housing are better able to focus when their apartment overlooks a grassy courtyard. Even these fleeting glimpses of nature improve brain performance, it seems, because they provide a mental break from the urban roil.

This research arrives just as humans cross an important milestone: For the first time in history, the majority of people reside in cities. For a species that evolved to live in small, primate tribes on the African savannah, such a migration marks a dramatic shift. Instead of inhabiting wide-open spaces, we're crowded into concrete jungles, surrounded by taxis, traffic, and millions of strangers. In recent years, it's become clear that such unnatural surroundings have important implications for our mental and physical health, and can powerfully alter how we think. [More]

All kidding aside, I think many of us in agriculture have experienced this effect instinctively, without fully appreciating its benefits.  It's why we look forward to days spent on tractor or combine (or at least until we got our cell phones).

Our brains did not evolve dealing with large groups or constant stimuli.

Other evidence suggests that 150 may be a functional limit on interacting groups even in contemporary western industrial societies. Much of the sociometric research on industrial and other comparable organisations, for example, has demonstrated that there is a marked negative effect of group size on both group cohesion and job satisfaction (as indicated by absenteeism and turnover in posts) within the size range under consideration (i.e. 50-500 individuals: see, for example, Indik 1965, Porter & Lawler 1965, Silverman 1970). Indeed, an informal rule in business organisation identifies 150 as the critical limit for the effective coordination of tasks and information-flow through direct person-to-person links: companies larger than this cannot function effectively without sub-structuring to define channels of communication and responsibility (J.-M. Delwart, pers. commun.). Terrien & Mills (1955), for example, found that the larger the organisation, the greater the number of control officials that is needed to ensure its smooth functioning.

Other studies have suggested that there is an upper limit on the number of social contacts that can be regularly maintained within a group. Coleman (1964) presented data on friendships among print shop workers which suggest that the likelihood of having friends within the workplace reaches an asymptote at a shop size of 90-150 individuals. (The small size of the sample for large groups makes it difficult to identify the precise point at which "saturation" is reached.) Coleman explicitly argued that this was a consequence of the fact that there is a limit to the number of individuals within a shop that any one person can come into contact with. Moreover, his results also seemed to suggest that the large number of regular interactants that an individual can expect to have within a large work group limits the number of additional friendships that can be made outside the workplace. [More]

The resurgent desire for agrarian living may not simply be a fad then, but a primordial urge. Given this intensity, taking it seriously would be of cardinal importance when dealing with urban dwellers.

Or in other words, listen carefully when non-farmers rhapsodize over our lifestyle.