Our Irrational Brains Are Killing Us


“Nothing is perfect. Life is messy. Relationships are complex. Outcomes are uncertain. People are irrational.” – Hugh Mackay

Our brains evolved over millions of years and made us the best hunter-gatherers the world had ever seen. We survived. We thrived. We spread across the globe and built great civilizations. 


Unfortunately, the same evolution that helped us survive has led to rampant foolishness. Brains that made sense of the savanna can be amusingly irrational in the modern world. We’re fish out of water. But while it took fish millions of years to adapt to life on land, we’ve only had a measly hundred years to go from small farming villages to towering megacities.  Our brains haven’t caught up–we still have mental fins instead of feet, and sometimes we flounder.


Here are some examples where our irrational brain might be killing us (or at least not helping us) in the most important parts of modern life.


Our Physical Health: Fat and sugar used to be hard to come by, and our ancestors had to conserve energy whenever they could. This led to brains that crave a fast hit of fat and sugar. We’re built to crave fast food and salty snacks and resist that morning jog. But our abundant sources of fast hits have made us more likely to die from consuming too many calories instead of too few.1 Humans spend up to four hours a day trying to resist these urges, and we often give in to our irrational desires, which may take years off of our lives.


Our Safety: The image of a spider on the steering wheel sends a shiver down most of our spines. But what about checking a text while driving? It’s the arachnid that puts us on edge, but we logically know that the distraction of digital devices while driving is the real killer, causing thousands of fatalities a year.3 We evolved a natural revulsion to creepy crawlies, but since automobiles and handguns are recent inventions, they don’t carry the same automatic fear factor. Our threat detection is outdated, and we often assess threats irrationally.


Our Finances: Even those of us who aren’t living paycheck to paycheck (and over 70% of us are) probably aren’t as good with money as we think.4 There was no need to save for retirement on the savanna, so planning for our retirement doesn’t come naturally. For example, we care more about equity than the bottom line: in one study, almost half of the people surveyed preferred to make less total money ($50K), as long as it was more than the people around them ($25K), opposed to more money overall ($100K), but less than their peers ($250K).5 This mentality might have been wise when not getting a fair share of meat could be the difference between your family’s life and death, but in an age of mortgages, tuition, and retirement for people living decades longer than our ancestors, it doesn’t make any sense at all.


Our Plans: We promise ourselves we won’t squander free time, that we’ll learn new skills or complete projects, but instead we irrationally turn to what’s comfortable, like video games, binge-watching TV, or social media. In fact, many products are designed to hijack the reward system that evolved to keep us alive and use it to hold our attention.6 If we read one more feed, or level up one more time, we feel the positive reinforcement of a reward and we think we’re happier. No one is going to die from bingeing a new show for ten hours straight, but it may not teach us a new skill or result in a ton of high-quality time with our kids, either. 


Our Mental Health: In the wild, it’s better to assume that it’s a predator rustling in the grass and be wrong than think it’s the wind and be eaten. These false positives are part of our evolution, and we often interpret intentions and patterns where there are none. The person that just cut us off probably didn’t do it on purpose (maybe they were looking at their phone), but we take it personally. It can even feel like inanimate objects have intentions of their own, so we punch the elevator button one more time as if that will get the stubborn thing moving.7 These reactions put people in a bad mood for no good reason, and though bad moods don’t kill, a high cortisol, stress-filled life isn’t healthy. 


People can’t help being irrational–human brains didn’t evolve for life in this millennium, and they misfire in all sorts of ways. People are driven by cravings beyond calorie counts, influenced by more than bottom lines on budget sheets, and we even think an inanimate object is intentionally ruining our day.  But with these factors in mind, we can take irrationality into account when designing everything from government-led economic systems to consumer experiences, and get people even closer to the results they’re hoping for.


  1. Unhealthy Diets May Be World’s Biggest Killer, WebMD, 2019
  2. The Evolutionary Roots of Irrationality, The Evolution Institute, 2018
  3. Distracted Driving, United States Department of Transportation, 2019
  4. Most Americans live paycheck to paycheck, CNBC, 2017
  5. Evolved Irrationality? Equity and the Origins of Human Economic Behavior, Mind the Gap, 2010
  6. Reward System, the Reward Foundation, 2017
  7. The Biology and Evolution of the Three Psychological Tendencies to Anthropomorphize Biology and Evolution, Frontiers in Psychology, 2018

*Image courtesy of Gratisography via Pexels.com

Scroll to Top