The world is full of those extraordinary things that we do without realizing that they are extraordinary: pointing fingers. Humans are humans because we have fingers.

Now our fingers seem, if anything, useful for grabbing whatever we want to grab, eating with modest lasciviousness, picking our noses or other orifices. And, millions of years later, when it occurred to them that they should count things, they once again resorted to their fingers: one finger, two, three, four fingers... That is why we have, in general, decimal systems.