Ironically, in the intervening 240 years, we've nailed this one: humans require both vitamin D synthesis from sunlight, and to not die from skin cancer caused by UV radiation. Thus, there's substantial selective pressure for darker skin in more equatorial regions and lighter skin in more polar (or more overcast) ones.

But we still haven't figured out how to extend freedom to each other all that reliably. We keep trying to take it away from each other again in various ways.