Some lizards’ blood has evolved to turn green, and scientists are now trying to understanding the relationship between green blood and possible protection against diseases like malaria and jaundice.

A new study called “Multiple origins of green blood in New Guinea lizards,” published Tuesday in the journal Science Advances, explains that high levels of biliverdin, a green pigment excreted in bile, is what causes the lizards’ blood to change colors. It’s also what causes bruises to have a greenish tinge.

High levels of bilirubin, a comparable bile pigment, is what makes humans sick with jaundice — but the lizards don't seem affected in the same way.

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"I find it just absolutely remarkable that you've got this group of vertebrates, these lizards, that have a level of biliverdin that would kill a human being, and yet they're out catching insects and living lizard lives," Susan Perkins, who is one of the authors of the study and a researcher at the American Museum of Natural History in New York, told NPR.

The study’s scientists have gone over a number of reasons as to why the lizards’ blood would evolve so much, including creating better camouflage and becoming distasteful to predators, but none of these hypotheses held up.

Recently, they’ve come up with the idea that the green blood might protect the lizards from parasites like malaria, but the theory is "pretty speculative," study co-author and biologist Christopher Austin told NPR.

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Still, test tube experiments did show that moderately high levels of bilirubin do seem to protect against infection of human malaria, according to NPR.

But Perkins notes that even if the green blood does prove to protect against malaria, it’s not 100% effective, as they did find a malarial parasite in a green-blooded lizard.

While the idea is still in early stages, research on green blood could result in a better understanding of malaria and jaundice, according to the study’s third author, Zachary Rodriguez.

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"It's rare in the animal kingdom," Rodriguez told NPR, "but because it does appear, this suggests there has to be some beneficial properties to green blood."

Understanding more about diseases like malaria is a key component to achieving global health goals around the world.

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