Why did lighter skin evolve near the poles? And why did darker skin evolve at the equator?

Explanation:

Human skin color reflects an evolutionary balancing act tens of thousands of years in the making. There’s a convincing explanation for why human skin tone varies as a global gradient, with the darkest populations around the equator and the lightest ones near the poles. Put simply, dark complexion is advantageous in sunnier places, whereas fair skin fairs better in regions with less sun.

allowed for the prediction of the properties of missing elements.