Each culture has its own definition of race due to a lack of a global standard. The only logical way to come to an agreement is by using science. If applied logically, it is universally accepted as true. Therefore, science is the only plausible way to determine race.
When scientists try to determine race, they look at specific genetic sequences instead of skin pigmentation. Science has determined that only a handful of genes dictate skin color. The other genes can differ more in same skin color groups than in cross skin color groups. In other words, two black men can have more genetic discrepancies than one of the same black men and a white man. For example, "individuals from sub-Saharan Africa and Australian Aborigines might have similar skin pigmentation (because of adapting to strong sun), but genetically they are quite dissimilar. In contrast, two groups that are genetically similar to each other might be exposed to different selective forces." The outcome of different forces is the development of two genetically similar groups with contrasting skin pigmentation. It would be rational to group people by overall genetic sequencing, not a general trait.
Some people argue that if members of a particular "race" are so diverse: why do people of African descent generally have hypertension, and why do Europeans have large, pointed noses? The reason why people of particular geographic regions and climatic zones have specific traits is evolution. Humans, like all forms of life, must adapt to their surrounding environment in order to survive. The truth is that those of African descent only have hypertension when they try to succeed in a repressive society. Those of African descent develop hypertension when they are not respected for who they are in all their environments. It is uncommon for an African in Africa to develop hypertension, because they are not as likely to be under racial scrutiny.