At the simplest level, if we trace back over the centuries, logically we should go back to one man and one woman from whom we all originated. Many religions believe that God created man and woman on this Earth. The creator had created humans and if we look back 200 million years ago almost all the continents were connected. So logically as the human race expanded and the continents broke, they gradually started to have an identity of their own based on the geographic landscape, weather, resources and over a period of time each continent have a more or less similar identity for face. But when we observe closely, there would be changes. For example to us all Chinese or Japanese will look the same, but there would differences that are obvious to the people of that nation. So, I think, God created us as one, passage of time and different ages has introduced obvious changes in our form and shape that gives us an unique ethnicity related to the land and its tradition.