What are some possible effects of natural selection of human characteristics?

There is strong evidence that all human beings have their origins in central Africa, and that migrations out of Africa starting roughly 100,000 years ago can account for the spread of humanity across the globe. These migrations can be genetically traced. If this is so, then natural selection might help account for many if not all of the major physical differences between different racial groups. People who migrated away from the equator lost the ability to produce large amounts of melanin in the skin. Changes in over-all stature/structure happened with groups that migrated very far north; these changes make it easier to endure the extreme cold conditions there. These are two examples of many that can be examined. These are not 'proofs' that natural selection has played a role in these differences. The question is asking for possibilities, not proofs.

The Genographic Project link will bring you to an absolutely wonderful site describing the genetic mapping of the human journey out of Africa starting roughly 100,000 years ago. Send them a genetic sample (order the kit through them) and get some amazing information about your deep ancestry. The information you get tells you nothing about current family ties-- only the general path of either your maternal line (through mitochondrial DNA) or your paternal line (through Y chromosome analysis). I do not work for and I do not represent the National Geographic Society, or the Genographic Project.