Are You Happy With the Size of Your Group?

Source: M Waheed Jadoon / Flicker

The population of the planet today is considerably larger than at any other time in human history. Between 1959 and 2042 the world population is projected to grow from 3 billion to 9 billion people, in the blink of an eye on an evolutionary scale (U.S. Census Bureau, 2016). The figure below provides some perspective on this time frame by graphically displaying the relatively recent explosion in world population.

This graph of the global population from 10,000 BCE to 2020 CE, adapted from the US Census Bureau data, shows very rapid growth since the 18th century. In the span of 40 years, from 1959 to 1999, the world population doubled from 3 billion to 6 billion. According to US Census Bureau projections, the world total will reach 9 billion by 2042.

Source: Source: U.S. Census Bureau, International Database,

We rely on psychological mechanisms shaped in our ancestral past to help us navigate the social and physical complexities and scale of the world today. For the first five million years of hominid history, there was almost nothing that could compare to the rate of population growth, particularly since the mid-1800s. As such, our psychological mechanisms, including emotions, decision making algorithms, and mate preferences, evolved under conditions that existed more than 10,000 years ago, when our ancestors lived in small, nomadic bands of hunter-gatherers.

On average, group size was likely maintained around 100-250 individuals. Based on correlations between primate brain size and social networks, Dunbar (1992) proposed that humans can comfortably maintain relationships with approximately 150 people. Because the size of the brain's neocortex effectively limits group size, many of our social adaptations are in tune with small cohesive groups with this capacity (Dunbar, 1993).

Modern city environments were non-existent for most of human history. The human brain evolved to manage social groups no bigger than 150 people and this poses problems in dense cities with populations that number in the millions. This can lead to adaptive acting out of character – for example performing like an extrovert when you are biogenically (naturally) introverted, which imposes physiological costs. It is energetically demanding to be agreeable when your instinct is to be disagreeable, or to act like you are open to new experiences and flexible when your instinct is to be structured and closed-minded.

A restorative niche is a physical place where we can “regain our first natures and indulge our biogenic selves” (Little, 2014, pp. 211). A restorative niche functions to reduce those costs and gives us the freedom to be ourselves in a comfortable environment that matches our personality. Urban design could help integrate such restorative niches that limit capacity to 150 or less.

Not only is it important to create spaces that meet our desires for group size, we need to find places that allow for the true expression of our personalities. Introverts may benefit from a quiet area that allows their overstimulated systems to return towards a resting baseline. In contrast, extroverts may actively seek out environments where people will engage with them. That is how they gain a sense of satisfaction. Most of us are ambiverts, somewhere in between the two extremes. That means we sometimes crave social interaction, but other times we need to retreat, and spaces should reflect this.