Oh this one is so cool!
It basically all boils down to Vitamin D! We need this essential vitamin to help our body build hormones and regulate calcium. Our bodies make Vitamin D when we are exposed to the UV rays found in sunlight. But as we all know, too much sunlight isn’t good because these UV rays can harm us. Melanin (the chemical that our bodies produce to darken skin tone and hair color) provides protection from UV rays by absorbing them. However, this means that the more melanin that is produced by someone’s body results in less absorption of UV rays and a decrease in Vitamin D production. But for someone living around the equator or in the tropics that doesn’t matter because there’s lots of sun all the time. So for humans living in these areas where there’s lots of sunlight year round, it’s beneficial to have darker skin to protect from the harm of UV rays. People living in these areas still get plenty of Vitamin D though because of that year round sunshine.
Now what about those who’s skin has less melanin, such as those found in the higher latitudes? Well with less sunlight year round, their bodies had to adapt to be able to get enough Vitamin D. So less melanin is produced by the body in order to absorb the lesser amounts of UV rays to make Vitamin D. Lighter skin is, therefore, more beneficial the farther away you go from the tropics.
So essentially:
Pro of Darker Skin tones
-Protection from harmful UV rays
Con of Darker Skin tones
-Less absorption of UV rays and less production of Vitamin D
Pro of Lighter Skin tones
-Greater absorption of UV rays and more Vitamin D production
Con of Lighter Skin tones
-Less protection from harmful UV rays (resulting in sunburns and, in extreme cases, skin cancer)
This is of course the biology answer. The social impacts of different skin tones is a whole different story that you can ask in the history section.
