The Science of Skid Marks

PrefaceHuman civilization has accomplished astonishing things. We have split the atom, walked on the Moon, mapped the human genome, built machines capable of thinking, sent spacecraft beyond the edge of the solar system, and invented approximately four hundred varieties of potato chip. Yet despite all of this progress, humanity remains periodically defeated by a small brown streak in a pair of underwear. It is one of the great equalizers of the human condition. Presidents, plumbers, professors, billionaires, mechanics, schoolteachers, astronauts, and people who insist they have never experienced such a thing are all equipped with essentially the same digestive machinery, and that machinery occasionally leaves evidence behind.This book is about that evidence.At first glance, the subject of skid marks seems much too ridiculous to deserve serious scientific attention. That impression disappears almost immediately once we start asking why they occur. A skid mark can involve digestion, intestinal motility, stool consistency, dietary fiber, hydration, muscle control, skin anatomy, friction, textile absorption, bacterial activity, laundry chemistry, wiping technique, toilet design, age, medication, diet, and sometimes an underlying medical problem. What appears to be a minor housekeeping embarrassment is actually the final visible result of an extremely complicated biological process that began hours or even days earlier with something placed on a dinner plate.