oneinchpunch via Getty Images Intelligent people are happier when they spend less time with friends, a new study suggests.

Are you an urban-dwelling loner who often prefers staying home with a book to going to a party? If so, psychologists say there could be a good evolutionary explanation for it. You may not have to spend a lot of time with your friends to be happy, according to research published last month in the British Journal of Psychology. In fact, if you're an intelligent person living in an urban environment, spending less time with your friends might make you happier. For the study, researchers analyzed data from a national survey of 15,000 adults between the ages of 18 and 28, which included information about their living environments, well-being, IQ and relationships. After controlling the data for socioeconomic status, the researchers found that people who were less intelligent than average (as measured by IQ tests) and lived in higher population-density environments (like big cities) reported lower levels of overall life satisfaction than those who lived in rural areas. The data also revealed that the more social interactions with close friends they had, the happier these lower-IQ adults reported themselves to be. However, the opposite was true for people with higher IQs than average. More intelligent people were more satisfied with their lives when they lived in a city, and they were happier when they spent less time with their close friends.

"The human brain in large part responds to the current environment as if it were the ancestral environment." Psychologist Dr. Satoshi Kanazawa

Why would the data show such results for highly intelligent people? According to the "savanna theory of happiness," the things that made our ancestors happy on the African savanna -- such as living in more rural environments in close hunter-gatherer tribes -- might also make us happy today. In other words, the average human brain may have evolved to function best in a rural environment with fewer people. When placed in an urban setting with a higher population density, our brains may signal for us to split into smaller social circles, Dr. Satoshi Kanazawa, a psychologist at the London School of Economics and the study's lead author, told The Huffington Post in an email. "The human brain in large part responds to the current environment as if it were the ancestral environment -- as if we were still hunter-gatherers living on the African savanna," Kanazawa said. Much like the "paleo diet," the savanna theory (or "paleo happiness") holds that the human brain and body still prefer the conditions of earlier times. "The human brain -- just like any other human body part -- is evolutionarily designed for and adapted to the conditions of the ancestral environment," Kanazawa said. "The brain therefore has difficulty comprehending and dealing with entities and situations that did not exist in the ancestral environment."