No one denies that what we indentify as races tend to share certain phenotypes. They do. Generally, if someone is described as “black” on their driver’s license, you can guess that that person is going to have certain physical traits concerning skin color, hair color and follicle shape, eye color, susceptibility and resistance to disease, even the skeletal structure all the way down to shape of the femur. Living together in a certain environment causes certain traits to be shared and selected for in a population. People whose ancestors lived in malarial climates in Africa will have a higher incidence of sickle-cell anemia, because it raises the population’s resistance to the disease.
However, look within a race and you’ll find just as many variations, if you want to. An African American is likely to have very different characteristics from a Masai tribesman, a Navajo will look very different from an Aleut or a Thai (despite the fact that they are/were lumped together in the category of “mongoloid race”), a blond Norweigian looks very different from a dark Italian (although both are “white”), and so on. We notice that certain observeable physical characteristics are common among certain ethinc groups and create mental constructs called “races” that lump together a very disparate group of people in a very murky way. It would actually be less arbitrary and make more sense to lump people together by a more definite and distict phenotype: blood type.
"Hey, Earl! Look at that AB holdin’ that type O’s hand! Hey, you!! Stay away from our type O women!!!