The Blood-Curdling Truth! This Animal Has GREEN Blood!

Deep within the forests of New Guinea and the Solomon Islands, a fascinating biological anomaly thrives: a group of skink species whose very lifeblood is a vibrant lime green. Unlike the familiar red of most vertebrates, the internal world of these lizards, classified in the genus Prasinohaema, is saturated with a green bile pigment called biliverdin. This striking coloration isn't confined to their circulatory system; their muscles, bones, and even their tongues share the same verdant hue. This unique trait stems from exceptionally high concentrations of biliverdin, a byproduct formed when hemoglobin from old red blood cells breaks down. In most animals, including humans, biliverdin is quickly processed further into a yellow pigment called bilirubin and then excreted, as high levels can be toxic (Review).

Indeed, the amount of biliverdin circulating in these skinks would be lethal to nearly all other vertebrates, causing severe jaundice and potential organ damage. Yet, these lizards not only survive but flourish with biliverdin concentrations up to 20 to 40 times higher than what would be fatal in a human. Scientists have been intrigued by how these skinks have evolved to tolerate such extreme levels of a typically harmful substance. Research indicates that this unusual green blood has evolved independently at least four separate times across different skink lineages, strongly suggesting it offers a significant adaptive advantage.

While the precise evolutionary benefit remains a subject of ongoing study, a leading hypothesis suggests that the biliverdin may offer protection against blood-borne parasites, particularly malaria. Similar to how bilirubin in humans can provide some defense against malaria parasites, the high levels of biliverdin in these lizards might make their blood an inhospitable environment for such pathogens, which are prevalent in their tropical habitats. Scientists are now exploring the genetic and physiological mechanisms that allow these skinks to resist biliverdin's toxicity, hoping that understanding this remarkable adaptation could one day lead to new insights for treating conditions like jaundice and malaria in humans.