There is no doubt that there are many different shades and skin colors across the world. There are even very different skin colors that live in the same climates. How did these different skin colors evolve? Why are some skin colors more prominent than others? No matter your skin color, it can be traced back to human ancestors that once lived on the continents of Africa and Asia. Through migration and Natural Selection, these skin colors changed and adapted over time to produce what we see now.
The answer to why skin color is different for different individuals lies within your DNA. Most people are familiar with the DNA that is found within the nucleus of a cell, but by tracing mitochondrial DNA (mtDNA) lines, scientists have been able to figure out when the human ancestors began moving out of Africa into different climates. Mitochondrial DNA is passed down from the mother in a mating pair. The more female offspring, the more that particular line of mitochondrial DNA will appear. By tracing very ancient types of this DNA from Africa, paleobiologists are able to see when the different species of human ancestors evolved and moved to other areas of the world like Europe.
Once the migrations had begun, the human ancestors, like Neanderthals, had to adapt to other, and often colder, climates. The tilt of the Earth determines how much of the Sun's rays reach the surface of the Earth and therefore the temperature and amount of ultraviolet rays that hit that region. UV rays are known mutagens and can change the DNA of a species over time.
Areas closer to the equator receive almost direct UV rays from the Sun all year around. This triggers the DNA to produce melanin, a dark skin pigment that helps block UV rays. Therefore, individuals that live nearer the equator have darker skin colors all the time, while individuals living the higher latitudes on Earth may only produce significant amounts of melanin in the summer when UV rays are more direct.
The DNA make up of an individual is determined by the mix of DNA received from the mother and the father. Most children are a shade of skin color that is a mixture of the parents, although it is possible to favor one parent's coloring over the other. Natural Selection then determines which skin color is the most favorable and over time will weed out the unfavorable skin colors.