A study from the University of London, for example, found that members of the remote cattle-herding Himba tribe in Namibia, who spend their lives in the open bush, had greater attention spans and a greater sense of contentment than urbanized Britons and, when those same tribe members moved into urban centres, their attention spans and levels of contentment dropped to match their British counterparts.
This should be the study:
https://www.researchgate.net/publication/235002874_Urbanizat...