Why did the humanity act in such ways?

Life began when Adam &Eva were sent to earth .The circle of life began and the human's became a poppulation.Black,whites,brown,(south east&
centeral asia)began to become race of peopele but
the thing that i dont usually get is why people moved to there own directions when they became a etnick group of human beings.The way the people use to think,isn't the way we think nowadays,you could
about what happend to notice way back when they were a etnick people you could imagine that people which where the same skin colour moved to hunt ther food &setteld
there for generations.But now those people which setteld those land and made a poppulation and a continent. My grandmother use to tell me when you see a family member you just know from "jiidka inaad isku dad tihin"(you know it from the flesh that you are related)

But was there wont no race found in that time so everybody was the same skin colour what would the world be and what kinda of environment would there be now,and did they move because it founded in that time aswell racism.
what do you think....?