We ride through life on the beast within us.Luigi Pirandello (1867–1936), Italian playwright

The Beast Within

We are, each of us, the miraculous product of four billion years of evolution. We still carry a few leftovers from our distant evolutionary past. Some of them aren’t pretty.

Did you know you’ve got the brain of a reptile? Yes, you. It sits at the top of your spinal column, and it’s the oldest and most primitive structure in your head. Over millions of years, humans developed higher-level mental functions—logic, memory, creative thought, language—but they’ve never replaced our reptilian brain. They’ve just added to it.

Our lizard brain is the source of our most basic instincts and emotions, also known as the four ...

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