No, humans are not black by default. Human skin color is determined by the amount and type of melanin, a pigment produced by special cells called melanocytes in the skin. Melanin comes in different forms, resulting in varying shades of skin color.
The primary determinant of skin color is genetic, and it is influenced by the geographic origin of one's ancestors. People with ancestors from regions with high sun exposure, such as Africa, India, and some parts of the Middle East, tend to have higher levels of melanin in their skin, resulting in darker skin tones. On the other hand, people with ancestors from regions with less sun exposure, such as Northern Europe, tend to have lower levels of melanin, resulting in lighter skin tones.
The variation in human skin color is a result of evolutionary adaptation to different environments. Darker skin provides better protection against harmful ultraviolet (UV) radiation from the sun in regions with intense sunlight, reducing the risk of skin damage and skin cancer. In contrast, lighter skin allows for more efficient synthesis of vitamin D in regions with limited sun exposure.
It's important to recognize that skin color is just one aspect of human genetic diversity, and people of all skin colors share a common ancestry. The concept of race, which has been used historically to categorize humans based on superficial physical features such as skin color, has been discredited by modern genetic research. Scientifically, there is more genetic variation within racial groups than between them, meaning that race is not a meaningful or accurate biological classification.
In conclusion, human skin color varies naturally based on genetic and environmental factors and is not a matter of being "black by default." It is a beautiful manifestation of the diversity within the human species.