The human brain is an organ out of time. It stands as evolved and best suited for daily life in the Pleistocene yet here it is, having to make do in a modern, high-tech, wired, and fast-changing world.

We have magnificent brains—and use them to believe nonsense and behave as fools. . . . We are enslaved to delusions and too often the servants of subconscious biases. . . . Our great challenge is to use our brains to overcome our brains.

Appreciate the magnificent brain you possess. Protect and nurture it. Strive to be a good skeptic and critical thinker so that fewer hours of your precious life will be squandered on dead-end beliefs. Always try to think like a scientist so that you might better know truth from fiction.

Every person is a collective, a vast and complex gathering of interdependent life. Any description of ‘human’ must acknowledge these intimate strangers. Our bond with microbes is such that they are not so much riders, parasites, and assistants as part human. And we, it’s becoming increasingly clear, may need to begin thinking of ourselves as part microbe.

We all believe silly things. What matters is how silly and how many.

In attempting to know, we engage in grand and meaningful acts. We use our human brains as time machines, to see and learn from the distant past and to travel forward thousands, millions, and billions of years. This young, patchwork organ that evolved to help ancient primates find food and water, maintain group relationships, achieve sexual intercourse, and imagine the next best tool now carries us to the very ends of the universe and beyond.

Critical thinking is the indispensable skill for smart living in modern society, and skepticism is the essential posture for the fully awake twenty-first-century human being.