Blacks have trouble clearing cervical cancer virus

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20. If those genetic markers were not evenly distributed in all types of dogs

then you could tell.

Humans don't have a uniform genetic makeup. As human populations spread out over the earth, different groups evolved differently as they experienced different adaptive pressures. And this extends well beyond skin color. Some good examples include:

1. Lactose tolerance. Wide variance across the world depending on whether populations depended on milk(horse or cow) for foods.

2. Sickle cell anemia - prevalent in populations with high incidences of malaria.

3. Hypertension - much more prevalent in dark skinned people. Salt retention in a high temperature environment is a beneficial adaptation as it prevents you from sweating away all your body's salt and dying.

You are right that race is a cultural concept. But it is not true to say that the color of someone's skin is not predictive of that person's genetic susceptibility to different diseases.