Adam and Eve had the right assortment of all genes, they were passed on to their children, that's why we have different races today! The people of that area were of Semitic/Arabic origin.
Note we are all "brown"... we are simply different shades.
Japheth is the father of the white race.. And Ham was the father of the black race! Here is the truth, Japheth's sons made up the Gentile nations north and west of Canaan. They were Greeks, Romans, Persians, and the Babylonians. What is called the European nations today. That's why they had a lighter complexion.
Ham's son Canaan made up the Canaanites that were in the Promised Land or near the Promised Land, and fought with Israel. They made up Palestine, Yemen, Saudi Arabia, Sudan, Egypt, Philistine, Libya, Hittites, Jebusites, Amorites, Babylon, and all the other "ites." Whew, very hot areas, no wonder they are so dark complected. One would be hard-pressed to get black skin as a curse.
Shem's sons made up the lineage of Abraham, the Godly line of the Jews. [1 Chronicles 1:24-27, Gen. 11:12-26]. Notice that chapter 10 is a record of the nations divided by their languages [v31] after the Tower of Babel account [11:1-9]. Chronologically chapter 11 is before chapter 10. As the peoples of the world were divided in different regions according to their languages, they adapted certain physical characteristics and skin pigmentation that we identify with their race.
There are three main races which are white, black, and Asian. We all have coloring matter in our skin which is called pigment, or melanin. Really there is one race and that is the human race, because we all have the same coloring matter or pigment in our skin. We are all born with a genetically fixed potential to produce a certain amount of melanin, and the amount increases up to that potential in response to sunlight..In other words, the sunlight draws the pigment or melanin to the surface of our skin, people who live in a hot climate with lots of sun shine have the darkest skin.
We need to be aware that one is not born with a genetically fixed amount of melanin, but rather with a genetically fixed potential to produce a certain amount in response to sunlight. Skin colour is governed by more than one pair of genes. Sunlight increases the melanin in our skin which makes our skin darker. Our body naturally produces melanin as a shield to the sun. Melanin is a dark colored pigment, so when you are in the sun your body produces more melanin to help protect you. The more melanin your body produces, the darker your skin gets.
People who lived in areas of intense sunlight developed dark skin colouration to protect against ultraviolet light and to protect their body mainly from folate depletion.
There is really only one race the human race. The Bible teaches us that God made from one man all nations of mankind. Acts 17:26.
www.answersingenesis.org/get-answers/features/adam-eve-skin-tones-one-race