We are not all one race in a biological sense, despite the rubbish spouted by most modern commentators, including a lot of people who should know better. Race is basically an extended family that has undergone extensive inbreeding for thousands of years. I am more closely related to a German than a Sioux Indian, as should be blindingly obvious to anyone who looks at me. It is not surprising that members of the same extended family share more characteristics than ones whose ancestors have not interbred for tens of thousands of years.
Race can be reliably determined by examining a person's skeleton. Race can be determined with extreme precision by DNA analysis. By looking at one or two genes, it can be hard to tell race. But looking at a bunch of genes works beautifully... as there is not one gene for race, but it is the relative proportions of many genes. Looking at groups of people, it is frequently easy to pick out the relatives because they share similar groups of traits. Thus it is for race.
