When it comes to understanding how all the different looking people could have come from Noah’s family, it might be helpful to think of dogs! It is a fairly well established fact that all domestic dogs have descended from an extinct wolf very similar to today’s gray wolf. Yet all these dogs come in so many shapes and sizes and varieties. They have not evolved, because evolution is about improved survival abilities. No one would say that any domestic dog is better equipped to survive than a gray wolf! Creation scientists believe (and have genetic research to back it up) that God built in all the genes necessary for survival and adaptation into the gray wolf, and the different domestic dogs are those original genes at work that have been rearranged, recombined, and even lost to give rise to the different dog species we see today.
To give a simple example of how this works – say a male and female dog migrate to a colder climate. They both have medium length fur, but with them they carry genes for longer fur and shorter fur. When they have offspring, the young with longer fur are going to be better equipped to survive than the young with shorter fur. Eventually, the dogs with shorter fur will either die out or migrate to a warmer climate. However, the gene for shorter fur has been lost in the group of dogs that remain in the colder climate. That is not evolution – in fact, it’s the opposite. Evolution proposes massive amounts of genetic information added to progress from single celled organisms to people like you and me. The dog population in the cold climate has adapted by losing genes – like leaving behind the supplies they don’t need. However, if the climate warms again, with no short fur genes left, that population of dogs will be less able to adapt. They would probably have to migrate again to survive.
Apply that same thinking to Noah and his family. When God created Adam and Eve, he also would have given them all the genetic information necessary for their offspring to adapt to many different situations. The same would be basically true of Noah and his family. It is genetically proven that parents with the right mix of genes could give birth to every skin shade we see among humans today. Essentially, we all have the same skin pigment – melanin. Those with a lot have darker skin, and those with less have lighter skin. Noah’s family must have carried in their genes the potential for every skin color, hair color and characteristic, every body size and shape, every eye shape, skull shape, nose shape, etc., that we see in humans today.
As time went on and the earth began to get repopulated after the flood, some people migrated south to Africa, some north to Europe, and some east to Asia. Those with darker skin pigment would be better able to survive in Africa, as they would be better able to deal with the harsh sun. Those with lighter skin would be better able to survive in Europe, as vitamin D is an essential nutrient we get from the sun. Those with dark skin who live in places where there is not as much intense sun have to get their vitamin D from other sources even today.
As for other characteristics like eye shape, nose shape, hair characteristics, etc., some may have conferred a survival advantage, while others simply may have been retained in a group of people by genetic luck of the draw.
To summarize, think of genetic variability like survival supplies. Noah and his family were carrying lots of supplies with them when they got off the ark. Gradually, as people migrated to different parts of the world, some of the items in their supplies were used and retained, while some were not needed and discarded, till you come to people like you and I today, who are much more specialized than Noah and his family were. We are well adapted for a specific climate and area of the world. But as a result, we have discarded a lot of our original supplies down through the centuries. We are not as adaptable as Noah and family would have been. But, God is very wise, because adaptability isn’t as big a deal now as it was in those days, with all the modern conveniences and technologies we have to help us survive in climates to which we are poorly suited.