Why does it feel like our brain, once designed to dodge a mammoth and find berries, is now keeping 24 tabs open at once and having a panic attack about it? Is this mental cacophony a glitch in the software, or the result of natural selection over-ambitious? The thousand thoughts racing through your mind simultaneously—ranging from "Am I happy?" to "Should I buy laundry detergent?"—may seem random. But perhaps they are the natural culmination of our evolutionary development.