This is Hidden Brain. I'm Shankar Vedantam.

Imagine you're an architect, but instead of drawing up a plan for a skyscraper or a bridge,

you've been asked to design the most sophisticated edifice in the universe, the human brain.

Getting to work at your drafting table, you'd likely prioritize accuracy.

You want this brain to perceive the world exactly as it is, a perfect mirror of reality.

In your blueprint, the good and the bad, the rewarding and the threatening, all would be treated the same.

Every event, every experience would be assigned equal weight, given the same attention,

and remembered equally.

But as any architect will tell you, there is a vast gulf between a design that works on paper

and one that actually survives the elements.

The same is true of our own minds.

The architect of evolution wasn't interested in making us objective observers or serene philosophers.

It wasn't trying to design a brain that took a fair and balanced view of the world.

It was building a survival machine.

To survive in a world filled with menacing predators, scarce resources, and social traps,

the brain had to be designed with a series of built-in biases. Those are

the same brains we have inside our heads today. It's why we focus more intently on some

flavors of experience rather than others. In turn, these biases shape what we perceive, how we respond, and even the course of our most intimate relationships.

This week on Hidden Brain and in a companion story on Hidden Brain Plus, the lopsided ledgers in our minds,

and how we can bring them into balance.

Thank you. Let's say you're a music critic attending a symphony. For two hours, 80 musicians play in perfect, breathtaking harmony.

The strings are soaring, the brass is precise, and the conducting is fluid.

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