Country roads, take me home...to my friends: How intelligence, population density, and friendship affect modern happiness (British Journal of Psychology)
"One of the fundamental observations in evolutionary psychology is that, just like any other organ of any other species, the human brain is designed for and adapted to the conditions of the ancestral environment, not necessarily the current environment, and is therefore predisposed to perceive and respond to the current environment as if it were the ancestral Environment"
For one group of people, seeing friends decreases happiness (Quartz)
"People who live in rural areas tend to be happier than those in urban areas, they argue, because our ancestors lived in groups of 150 people and struggled to maintain cooperation and reciprocity in larger groups. Living in larger groups could then create feelings of unease and discomfort."
Modeling Users' Activity on Twitter Networks: Validation of Dunbar's Number (PLoS)
"The limit imposed by neocortical processing capacity appears to define the number of individuals with whom it is possible to maintain stable interpersonal relationships. Therefore, the size of the brain's neocortex represents a biological constraint on social interaction that limits humans' social network size to between 100 and 200 individuals"