To survive, reproduce, and flourish, species have to develop ecological adaptations to their environment. Humans have mastered the art of living in every possible climate and landscape on earth—provided we’re in groups. Our natural environment, the one we’ve evolved special adaptations to, is the presence of other humans.
Since humans and chimpanzees split from a common ancestor about 6-7 million years ago, evolution has gently tweaked our genetic material 15-20 million times. 1 When rivals of our ancestors, possibly baboons, developed the ability to digest unripe fruit and began encroaching into our foraging territory2, we were pushed out to the savanna, closer to larger predators with bigger teeth. And so, 400,000 years ago, forced out to the edge and facing starvation, our ancestors competed with larger fanged-and-clawed animals by hunting together, as one large “super-organism.”
Because of this “play nice or die” conundrum, an immense evolutionary pressure emerged to select others who made good teammates. Human life depends on successful group living—foraging and hunting cooperatively—because we’re smarter together. We needed people to collaborate, help us do what needs to be done, and then only take their fair share. The fringes may be more interesting, but they’re always a precarious place to be. Humans are chimps who learned how to work together for common goals—to collaborate, follow rules, and share. Our species’ need for interdependence has changed our brain and basic cognitive functions. 3
THIS IS YOUR BRAIN ON GROUP LIVING
All of the things we need to do to stay alive—breathing, moving, getting food, and finding some allies—require energy, but we can’t use more energy than we consume. Behavioral ecologists, who study behaviors that result from natural selection, refer to this as the optimization premise. Our default motivation of self-preservation requires us to be picky about energy expenditure, and since the brain itself an organ with self-regulatory capacities, it’s an expert at knowing when to use itself.
Survival demands that we have a deeply-ingrained need to belong, and connect with others through affiliation, acceptance, and belonging. (If you bring something special to the group, you can be granted status, which acts as a buffer against rejection.) Cultures are just groups of brains that have been working together for so long that it’s hard to think beyond the rules, since every part of our lives takes place within its constraints. What feels like the natural way to do things is just what we’re used to; “normal” depends on our cultural and social norms: what you should wear depends if you’re going to an art fair, a Halloween party, or a funeral. “How we do things around here” varies widely between groups and situations.
SKIP IF YOU KNOW ABOUT THE ASCH CONFORMITY STUDIES
In a famous study, researcher Solomon Asch held up a poster with 1 line on the left, and 3 lines on the right hand. Look at the line on the left, and raise your hand when the researcher pointed to the line on the right that was the same length.
“As the number of comparisons is few and the group small, I will call upon each of you in turn to announce your judgments, which I shall record here on a prepared form. Please be as accurate as possible. Suppose you give me your estimates in order, starting at the right in the first row, proceeding to the left, and then going to the second row.”4
Everyone in the room was in on the trick, and raised their hands at the wrong time: there was only 1 actual subject in the room at a time! The room full of confederates (fakes/actors) raised their hands when the researcher pointed to a line that was clearly a different length. What did the real subjects do? While a few daring individuals held out, 75% of the subjects ended up following suit, raising their hands at what was clearly the wrong answer.
MOST OF LIFE’S ANSWERS AREN’T ABOUT LENGTHS
Reading about this study from the comfort of your home is one thing: just raise your hand when the guy points to the one line that looks like the other line, I can do that!5
But actually being faced with the following dilemma is another: what would you do if every single person around you was doing something that was very clearly wrong?
Roughly 99% of the answers we want in life are less cut-and-dry than ‘how long is this line’: what’s the best new restaurant in the neighborhood, the best album of the year? What’s the best productivity app? Which TV show should I binge next? Where should I put my hands? Is that funny? How soon can I leave without being considered rude, should I bother texting back, do these pants make me look fat, and does this shirt make me look like I’m definitely going to die alone?
GROUPTHINK IS EFFICIENT
If we consider every answer from every perspective, we’d never get anything done: we’d die of starvation, trying to think of where to get some food. Our success as a species may really come down to copying others, as Joseph Heinrich argued in The Secret of Our Success.
Most answers in life aren’t the kind on simple math tests that can be proven objectively. Most depend on opinions.
When we’re thinking about the answer to a question, we’re not only considering the validity of the answer. For the sake of survival, we also need to consider our reputation—and how our actions make us look in the eyes of others. (Being agreeable, in fact, is fundamentally about a desire to maintain good relationships; if you find yourself on a date with someone who enjoys playing “Devil’s Advocate,” run. And people who claim that testing and workshopping ideas requires arguing are also to be avoided for the sake of one’s mental health.)
Everything about the way our mind works makes sense through the lens of evolution. Adjusting our beliefs to fit those around us checks all the boxes: Our brains incorporate the social information and make something even more rewarding. Social influence is derived from the principles of cognitive economy—learning from others is more time and cost-effective than sampling everything on our own.6
DYING ALONE: A THING TO BE AVOIDED
You’ve probably heard how our stress “fight or flight” response, developed to promote survival, now goes off when we’re dealing with things that aren’t a direct threat to our lives: shitty bosses, an unexpected bill.
Anything that sends a signal that we’re not the alpha in the group also sends us scrambling, since our brain’s response often starts us down a path that leads to I’M GOING TO DIE ALONE. That’s why social woes can sting for so long: the idea of being rejected, being made fun of or laughed at, being criticized—all very bad things.
The problem with groupthink is that we often don’t realize how much we’re selling ourselves short. Why aren’t you starting your own company? Doing that thing? What you consider to be the truth or reality is merely a reflection of the beliefs of those close to us.
 Harry Smit. The Social Evolution of Human Nature: From Biology to Language. (New York, NY: Cambridge University Press, 2014): 31.
 Michael Tomasello. A Natural History of Human Thinking. (Cambridge, MA: Harvard University Press, 2014): 34-36.
 Michael Tomasello. “The Ultra-Social Animal.” European Journal of Social Psychology 44 (2014): 187–194.
 Solomon Asch. “Studies of Independence and Conformity: I. A Minority of One Against a Unanimous Majority.” Psychological Monographs 70, no. 9 (1956). Whole No. 416.
 See also Solomon E. Asch. “Effects of Group Pressure on the Modification and Distortion of Judgments,” in Groups, Leadership and Men, edited by Harold Guetzkow. (Pittsburgh, PA: Carnegie Press, 1951.) Solomon Asch. “Opinions and Social Pressure.” Scientific American 193, no. 5 (1955): 31-35. B. R. Hergenhahn and Tracy B. Henley. An Introduction to the History of Psychology, Seventh Edition. (Belmont, CA: Wadsworth, 2014): 591.
 Lane Beckes and James A. Coan. “Social Baseline Theory: The Role of Social Proximity in Emotion and Economy of Action.” Social and Personality Psychology Compass 5, no. 12 (2011): 976–988.
 Anne Fagot-Largeault. “Anthropological Physiology: von Uexküll, Portmann, Buytendijk,” in Neurobiology of “Umwelt”: How Living Beings Perceive the World, edited by Alain Berthoz and Yves Christen. (Springer-Verlag Berlin Heidelberg, 2009): 1-5.