Notch counting is the earliest mathematical activity of human beings. In ancient times, human beings had the need to count the labor of fishing, hunting and fruit gathering. Count with fingers, stones, knots or nicks on branches, animal bones, etc. 1937, an archaeologist found a notched wolf bone in Moravia, Czechoslovakia. There are 55 nicks on a bone, and every five nicks are a group. It is generally believed that the age of this wolf bone is about 30 thousand years ago. This is the earliest counting evidence.

Bone tissue is composed of living cells and minerals (mainly calcium and phosphorus), which makes bones have solid physical properties. Bones come in different shapes and sizes. For example, arm bones are long bones, wrist bones are short bones, sternum and skull are flat bones, and vertebrae are irregular bones. Adult bones are mainly composed of two kinds of tissues: hard and dense bones on the outside and porous cancellous bones on the inside. The thigh bone in the long bone or femur is filled with fat called yellow bone marrow.