Why are the Japanese short?

When I first thought about it, I also thought about pygmies. Short people. Why are they low? Obviously, the Chinese and the Japanese are the same race. But the Chinese are tall and the Japanese are not. Of course, I began to think about this topic, to look for analogues. For example, pygmy elephants. Dwarf elephants live on the islands. Stop. On islands. As do the Japanese. The analogy is quite obvious, isn't it? I began to think further. What affects growth? The growth of any creature is affected by the force of gravity of the planet. It turns out that the force of gravity is higher on the islands? I tested this theory and... it's not true. The force of attraction is the same as everywhere else. Then why are the Japanese short?