Mysterious New Guinea Lizards Have Toxic Green Blood, and Scientists Are Puzzled About Its Purpose

In the wild, some anomalies even confuse the most experienced biologists. Certain species bypass laws however considered as universal, revealing still unsuspected mechanisms. This is precisely what the recent study of arboreal lizards shows with a strange physiological particularity. Their green blood, far from being a simple whim of evolution, could well open unexpected tracks for human medicine.

This biological paradox surprised Christopher Austin, herpetologist at the Louisiana State University, who has been studying these species for over twenty years. He found that all their internal tissues, from bones to mucous membranes, share this green color, without apparent impact on their health. In his eyes, the existence of these reptiles constitutes an extreme physiological anomaly, a case of reverse toxicity where what kills most of the organisms seems here harmless.

The most striking is that this particularity has not developed only once. Green blood appeared independently at least four times in different lines of Australo-Pacific scints. This suggests that there is, somewhere, an evolutionary advantage in this biological strangeness.

How a deadly pigment becomes an evolutionary asset

The question of why persists. Why would the evolution have favored a toxic pigment? Some hypotheses advance internal camouflage, others evoke protection against parasites. The idea that green blood can make lizards less appetizing for predators has been tested, without success. Even captivity birds do not hesitate to devour them. The taste tests carried out by the researchers, themselves, have revealed any notable difference between the red and green species.

On the other hand, a more promising track emerged from the potential link between biliverdine and resistance to infections. We know that certain levels of bilirubin offer some protection against malaria in humans. However, New Guinea lizards are frequently exposed to plasmodium-related parasites, malaria agent. Researchers from the American Museum of Natural History, cited by NPR, therefore suggest that the accumulation of biliverdine could play a role in defense against these pathogens. Even if this hypothesis remains to be confirmed, it could explain the evolutionary convergence observed.

Furthermore, a 2025 study published in the Journal of Heritity suggests the existence of a duplicated and modified copy of a protein related to alpha – foods, which could link biliverdine and limit its toxicity. This mechanism remains to be confirmed, and the presence/absence of albumin in these lizards is not established.

From the tropical forest to the laboratory, a new field of research

The capacity of prasinohaema to support lethal concentrations of biliverdine opens up new biomedical perspectives. Understanding how these reptiles neutralize such a toxic substance could revolutionize certain treatments related to liver disease. In mammals, the accumulation of bile pigments causes oxidative stress, inflammation and cell degeneration. Green reptiles seem to have found an effective bypass of this process.

The fine analysis of their genome also shows a very high rate of transposable elements, these DNA fragments capable of modifying genetic expression. This constant genetic reshuffle could have favored, in some cases, the emergence of proteins capable of linking biliverdine. If this hypothesis is confirmed, it would therefore bring an additional explanation to the spectacular tolerance of these reptiles, according to Iflscience.

This unique animal model could thus become a key to understanding not only toxic waste management in the body, but also the adaptation mechanisms to hostile environments. The genomic exploration started by the Brigham Young University team from a simple sample kept in a museum for more than twenty years has made it possible to cross a course in research. Thanks to this unprecedented resource, biologists can now consider finer comparisons with other species and, perhaps, identify concrete biomedical applications inspired by these lizards with green bowels.