The previous paleontology and paleoanthropology sections tried to answer the question: How are humans different from other life? This section on human variation asks the question: How are humans different from each other?
Go back and review the Mendelian traits lab. Should we take everyone in class with attached earlobes and call them a race? This sounds silly, but what I hope you can appreciate is that from a biologist's perspective, assigning a race to people based on an arbitrary range of skin colors and facial features is even sillier. Anthropologists have a kind of dissociative identity disorder when it comes to race. When you ask people about human variation, the first thing that usually comes to mind is race – they acknowledge the concept. So race exists, and cultural anthropologists study it as a learned behavior. Physical anthropologists split between denying the existence of race, and seeing it empirically in bones. Forensic anthropologists still like to talk about being able to "race a bone", which means establish the ancestry of an individual from the morphology of skeletal remains. Since the early 1900s, most anthropologists in all subfields have actively opposed racism.
More biologically significant kinds of human variations include our practically invisible co-evolution with disease, and solving important riddles such as 1) If men are from Mars, and women from Venus, does that make Earthlings intersexual? and 2) What walks on four legs in the morning, two legs in the afternoon, and three legs in the evening?