Answer: All fingers, toes, feet, and palms are covered in small ridges. These are raised portions of the skin, arranged in connected units called dermal, or friction, ridges. They help us with our grip on objects that we touch. When these ridges press against things, they leave a mark, an impression called a fingerprint.
You take any of the "signs of change in populations of organisms and their environments". For imagine, Australopithecus (early man) turning to Homo sapiens. In that way they could tell that you took this journey.