Comment by shagie

I am inclined to believe that the pressure for more melanin (cancer, sunburns) is a more rapid adaptation than decreasing it.

Human skin pigmentation, migration and disease susceptibility - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3267121/

> Human skin pigmentation evolved as a compromise between the conflicting physiological demands of protection against the deleterious effects of ultraviolet radiation (UVR) and photosynthesis of UVB-dependent vitamin D3. Living under high UVR near the equator, ancestral Homo sapiens had skin rich in protective eumelanin. Dispersals outside of the tropics were associated with positive selection for depigmentation to maximize cutaneous biosynthesis of pre-vitamin D3 under low and highly seasonal UVB conditions. In recent centuries, migrations and high-speed transportation have brought many people into UVR regimes different from those experienced by their ancestors and, accordingly, exposed them to new disease risks. These have been increased by urbanization and changes in diet and lifestyle. Three examples—nutritional rickets, multiple sclerosis (MS) and cutaneous malignant melanoma (CMM)—are chosen to illustrate the serious health effects of mismatches between skin pigmentation and UVR.

Also of interest - The colours of humanity: the evolution of pigmentation in the human lineage https://royalsocietypublishing.org/doi/10.1098/rstb.2016.034...

The different pathways for depigmentation are different.

> The fact that depigmented skin evolved independently in the ancestors of modern Europeans and East Asians suggests that at least two (and probably more) distinct genetic mutation events occurred and that multiple loci underwent positive selection in these two regions receiving relatively low levels of UVB. The most likely reason for this was that it was associated with a loss of skin pigment that favoured vitamin D production under conditions of low UVB.