Recent work in Darwinian medicine has suggested that physiological neonatal jaundice (PNJ) might serve an adaptive function in scavenging reactive oxygen species that in later life are removed by the mature antioxidant enzyme system in the liver. This treatise examines this hypothesis in light of novel epidemiological and genetic findings which suggest that the incidence of PNJ is significantly increased in East Asian populations. Though found across all ethnic groups, it has been established that neonates of East Asian origin are at a significantly greater risk of developing PNJ, with more than one studying finding the incidence to be near double. For any Darwinian explanation of physiological neonatal jaundice to be considered in clinical circles, it is essential that the elevated incidence of PNJ in this population be explained both mechanistically and in terms of adaptation. Recent work has linked PNJ to a specific enzyme polymorphism, a variation of the UGT1A1 gene, in the glucoronidation pathway which is essential for bilirubin metabolism and is strongly correlated with ethnic origin. In this paper it is hypothesized that the elevated incidence of PNJ in East Asian populations is not random or due to a flaw in the system but rather due to an evolved mechanism. Two potential pressures which might have selected for an elevated neonatal bilirubin in East Asian populations versus other ethnic groups are a diminished ability to reduce harmful oxidant radicals due to variations the P450 liver metabolic pathway and the endemic nature of Hepatitis B in the Asia-Pacific region. This is the first work to attempt to explain PNJ through a Darwinian yet clinically relevant lens while suggesting a specific proximate mechanism that is correlated with a pre-existing evolutionary environment and can be associated with differential reproductive success.
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