We all belong to a single species, Homo sapiens sapiens, the human being. What certain people call “races” are groups of humans formed according to chosen criteria, such as skin color. However, all humans have 99.9% of their genes in common. So, biologically, “human races” do not exist; just one species, the human species.
So why do people talk about “race”?
Because some people are racists and want to classify humans according to their appearance. During the Second World War, Nazis thought they belonged to the aryan race: humans with white skin, blonde hair and blue eyes. The existence of the aryan race wasn’t scientifically proved but it allowed Nazis to exclude the rest of the population. Racists often use the idea of race to say they are superior. This allows them to exclude or persecute others that they say are generally inferior.
For example, in South Africa, during apartheid, from 1948 to 1991, Whites and Blacks didn’t have the same rights and Whites were privileged. There have always been people who use this nonscientific idea of race to reject those who don’t look like them. Even today, some people still use racist ideas to accuse part of the population of being responsible for the country’s problems.