Why You're Not as Rational as You Think

I recently attended a seminar on human evolution, behavior, and the brain. The speaker walked us through something that fundamentally changed how I see myself and everyone around me. Not in a self-help way. In a biological, evolutionary way.

Here's what I understood. In my own words.

The Numbers That Should Humble Every One of Us

Before we get into why we behave the way we do, let's set the stage.

6–7 million years. That's how long our ancestors have been walking upright on this planet.

2 lakh years. That's how long Homo sapiens, modern humans, have actually existed. Barely a blip.

5,000 years. That's all civilization is. Law, religion, culture, mathematics, discipline. Everything we're supposed to live by fits inside this tiny window.

ExpandHuman evolution timeline — from early hominids to Homo sapiens

Source: Wikimedia Commons, CC BY 4.0

Sit with those numbers for a second. The gap between them is the whole point.

Everything modern life expects from us:

Sit still in a classroom.
Follow rules you didn't write.
Suppress the urge to react when someone provokes you.
Make "rational" decisions.
Delay gratification.

All of that is built on 5,000 years of civilization. But the brain doing all this was shaped over millions of years of something completely different.

Life back then wasn't complicated. It was just dangerous. Every single day was eat dinner or be dinner. Your survival depended on how fast you could fight, run, or freeze. That was the job. That was all there was.

And then, practically overnight in evolutionary terms, we invented agriculture, cities, laws, and office meetings.

Our brains didn't get the memo. They still haven't.

Why Sports Exist (And It Has Nothing to Do with Fitness)

Here's a question that seemed simple but made me think differently: why are sports popular?

Not what sport you like. Why the concept exists at all.

Think about football rationally for a second. Twenty-two people running around a field, trying to put a ball into a net. If you handed everyone their own ball, they could each enjoy it privately. So why the competition? Why the tribalism? Why the roaring crowd?

The answer is in our evolutionary history. For millions of years, life demanded aggression, physical exertion, and high-stakes competition. That's what kept you alive. But civilized society can't function if we're aggressive in the streets. We needed somewhere to put that energy.

Sports are a formalized, socially acceptable release valve for primal instincts.

The goal post is the tiger you wanted to kill.
The opposing player is the rival you needed to outrun.
The crowd watching is experiencing the same thrill vicariously, feeling it without actually doing it.

This also explains something about innovation. Societies that invest heavily in sports tend to be more innovative. Once that pent-up primal energy gets a healthy release, the mind is freer to think creatively. Suppressed aggression creates stress. Stress blocks imagination.

The Three Brains Living Inside Your Head

ExpandThe Triune Brain Model — three evolutionary layers stacked inside your skull

This is the part of the seminar that really clicked for me. The Triune Brain Model: three layers of brain, each from a different era of evolution, all stacked inside your skull right now.

The Reptilian Brain

This is the brain we inherited from reptiles. Pure instinct. No emotions. No feelings. No thought. It runs on four things:

Survival — eat, breathe, reproduce.
Aggression — fight what threatens you.
Alarm — react before you think.
Dominance — establish where you stand in the group.

A dinosaur with a brain the size of 50cc could move a 200-foot body, hunt, and defend itself entirely on instinct. When a ball flies at your face and you duck without thinking, that's this brain. The two most powerful triggers it responds to are alarm and power, because those are the things that determined whether you lived or died.

The Mammalian Brain

As we evolved into early mammals, a new layer formed around the reptilian brain. This is where emotions live:

Passion — the drive toward what you want.
Trust — who you let in and who you don't.
Prestige — your sense of status in the group.
Desire — craving, wanting, reaching.
Intuition — knowing without being able to explain how.

What we call "gut feeling" actually originates here, not in the stomach.

Most of our daily decisions are made here. Not by logic. By emotion.

The Neocortex

The uniquely human brain. The thinking brain. The part that writes poetry, solves equations, and builds cities. The prefrontal cortex, the front portion of the neocortex, is especially developed in humans.

And here's the uncomfortable truth: the neocortex does not make decisions. It rationalizes them after the fact.

Where Feelings Actually Come From

We say emotions come from the heart. We say "gut feeling." Greeting cards are shaped like hearts. Love songs reference the chest, the stomach, the pulse.

None of that is biologically accurate.

All emotions originate in the brain, specifically in a small region called the amygdala, part of the mammalian brain. When ancient humans didn't know where feelings came from, they made their best guess. The heart races when you're scared or in love. The stomach tightens under stress. So naturally, those became the symbols.

Those early guesses entered culture, became language, and eventually became permanent. Nobody kept questioning once the answer felt poetic enough. But it's the brain, all the way down.

The Real Decision-Maker Is Not Who You Think

Here's the most unsettling part of everything I learned.

You never really think before making a decision. You decide emotionally, then spend time convincing yourself it was rational.

This is called backward rationalization. Your mammalian brain makes the call. Your neocortex, the so-called rational brain, then builds a logical story for why the decision was right.

The seminar speaker framed it well: people who say "someday I'll start my business" have already made the emotional decision that it's too scary. Their rational brain then keeps generating reasons to wait, to plan more, to be "ready." The real block isn't logical. It's emotional.

This also explains crime. Rationally, there is almost no good reason to commit violence. But at the moment of rage, the mammalian brain takes over and the neocortex goes quiet. People do things they spend the rest of their lives regretting.

The Modern World Barely Triggers Your Oldest Brain

Here's the irony of modern life: the brain that drives the most powerful decisions, the reptilian brain, almost never gets triggered anymore.

Real alarm — a predator, actual physical danger — barely exists in daily life. We've replaced it with manufactured alarm:

Insurance ads: "If you don't buy this, something terrible will happen."
Fear of failure.
Social anxiety.
The 24-hour news cycle, optimized to keep the threat signal alive.

These are pale imitations of real danger, but they're the only alarm signals most of us receive now.

So nearly all our decisions are made by the middle brain, the emotion brain. Passion, trust, prestige, desire. We're driven by feelings we can't fully articulate, covered with a thin layer of logic we applied after the fact.

The Logic Puzzle That Proves It

The seminar ended with a puzzle. Read it once and answer honestly.

ExpandJack, Ann, and George — the logic puzzle visualised

Jack is looking at Ann. Ann is looking at George. Jack is married. George is not. Is a married person looking at an unmarried person?

A) Yes B) No C) Cannot be determined

Almost everyone says: cannot be determined.

But the answer is yes. We don't know Ann's marital status, but there are only two possibilities. If Ann is married, she is looking at George, who is unmarried — so yes. If Ann is unmarried, Jack, who is married, is looking at her — still yes. In both cases the answer is the same. We stopped thinking the moment we hit the first piece of missing information and called it uncertainty.

Bertrand Russell, one of the greatest logical thinkers of the last century, wrote 35 books on logic and said he had never met a truly rational person in his life.

Because here's the problem: our entire education system, our work, our institutions are designed around rational thinking. But the brain making all our decisions is wired for emotion. The thinking brain is just the narrator. It doesn't write the story.

What I'm Still Sitting With

Understanding this doesn't make you immune to it. I still get frustrated in traffic for no logical reason. I still feel pulled toward certain decisions I can't fully explain. The animal inside isn't going anywhere.

But knowing why it happens, knowing that millions of years of evolution didn't disappear when we invented spreadsheets, changes how I look at myself and everyone around me.

We're not irrational. We're just running very, very old software on a relatively new world.

This is part 1 of 6 in the series on Evolution, Behavior and the Brain.