Theory 50/Organism/Skin pigmentation
Skin Colour Balances Two Needs
The claim
Skin pigmentation is set by the ratio of UV protection needed to vitamin D synthesis needed, so the same population shifts with latitude.
01Mechanism
Melanin blocks UV, which protects folate but reduces vitamin D production; the optimum is where the two costs balance.
02Prediction
Pigmentation should track the ratio across latitudes.
03Refutation
Pigmentation tracking UV alone would remove vitamin D.