How did the different races come about if you have one ancestor?

Answer 1

No-one has only one ancestor. However, the genetic code for all races can be contained in the DNA of two original ancestors (biblically speaking - Adam and Eve). There is actually very little genetic difference between the major peoples of the planet, so it did not take long for diversity to be expressed in various locations.

Answer 2

Of course the different races could not have evolved if we only had one ancestor just a few thousand years ago, whether Adam or Noah. but that is not how it happened: modern humans have been around for hundreds of thousands of years, enough time for different groups to adapt to their environments. Dark skin is not ony unnecessary in colder climates, but lighter skin enables more ultraviolet radiation to be absorbed so as to produce sufficient vitamin D. Likewise, longer noses enable the air to be warmed as it is breathed in. Long, high noses are also useful in desert environments. We can see that the differences among the human races are largely the result of adaptation to the enviroment, but this can not occur in the few centuries that The Bible would allow.