Evolutionary biologists know why humans spend disproportionate energy on negative thoughts compared to positive: Teasing out threats, real or perceived, is a basic tool of survival.
Three a.m. isn’t the only time negative thoughts seize us. Even when we’re at ease, evolutionary instincts cause us to seek out whiffs of threat, real or imagined. Commonly called the human "negativity bias," we train our mental energy on perceived danger, releasing cortisol and triggering flight or fight instincts that have served mammals from the beginning.
