I remember an old vitamin D book – I believe it was Feldman’s Vitamin D – that going down the Transsahara Route (Algier-Lagos) human skin color gets always darker towards Tamanrasset due to increased solar power (also known as Loomis Hypothese).
Let’s look at three maps now.
The above map does not match the skin tones.
Neither does a new vitamin D map published last week in the Lancet
Although the maps are still patchy, I think the Loomis hypothesis is wrong.