Why did Shang and Zhou divination use turtles and animal bones?

The Shang and Zhou dynasties used tortoise and animal bones for divination for the following reasons:

First, the tortoise was a god beast in Shang and Zhou Dynasties, which could achieve the effect of harmony between man and nature.

In fact, in the Shang and Zhou Dynasties, everyone knew that the tortoise was a very long-lived animal and a spirit beast. Therefore, the ancients thought that divination with the shell of a god beast could tell God's will, and this is the way of communication between man and heaven. Of course, there were some animal bones at first, but gradually more and more people began to use tortoise shells, because tortoise shells would be easier to get.

Second: the shell looks like a circle advocated by the ancients.

Where the ancients believed in the circle, the turtle shell just echoed this. The back of the turtle shell arches like a sky, while the belly of the turtle shell is very flat, indicating the earth. Therefore, if you use tortoise shells for divination, you can know bad luck and wealth and so on. Moreover, in the Shang and Zhou Dynasties, people baked turtle shells with torches, so that cracks would form on the turtle shells, and the crack lines were related to gossip, so the ancients used to use it to predict state affairs and weather.

Third: turtles are relatively easy to get.

At the beginning, although some people used animal bones, it was only useful after hunting prey, and it was a wild animal, but it was still quite difficult. Later, people discovered turtles. It is much easier to find a turtle than to hit a wild animal. Moreover, turtles were sacred at that time. After all, it is said that one of Longsheng's nine sons looks like a tortoise, and the tortoise is also related to longevity.

The ancients were very persistent about being able to live a long life, especially the king wanted to live a long life. Therefore, the tortoise was able to get divination directly at that time. In fact, it also meant to use its magical power to expect longevity.