Do you live in the American continent? Look at the skin tone of most people you find in the streets. Go to a library and try to find out what was the average skin tone in your region 600 years ago. Compare both.

Thinks have been spreading for quite a while. Migratory species are older than ourselves. Jet stream can carry spores over oceans. World commerce is older than you think. Wars and migratory movements has always been a part of our civilization.