In 1969, two biologists wrote about three lizards from New Guinea whose insides were green. The color ranged from a deep blue-green to a vivid lime hue, and it was everywhere. The lizards’ bodies, when dissected, revealed green bones, muscles, and blood. Their mouths, when opened, were green. Their eggs, when held up to a light, looked green inside their shells.
Christopher Austin was just 3 years old when the two scientists, Allan Greer and Gary Raizes, wrote about the lizards, and he was 22 when he finally learned about them. But he quickly became enthralled. Green! Why green? “It’s very, very striking,” he says.
Animal blood comes in a rainbow of hues because of the varying chemistry of the molecules it uses to carry oxygen. Humans use hemoglobin, whose iron content imparts a crimson color to our red blood cells. Octopuses, lobsters, and horseshoe crabs use hemocyanin, which has copper instead of iron, and is blue instead of red—that’s why these creatures bleed blue. Other related molecules are responsible for the violet blood of some marine worms, and the green blood of leeches. But the green-blooded lizards use good old hemoglobin. Their red blood cells are, well, red. Their green has a stranger origin.
Red blood cells only live for four months or so, and when they die, our bodies recycle the iron within them. That process inadvertently creates a green pigment called biliverdin, which is then converted into a yellow one called bilirubin. Both of these are toxic, and our livers quickly filter them out of our blood. When you get a bruise, the unsightly green and yellow colors come from the biliverdin and bilirubin unleashed by dying red blood cells. When infants get jaundice, that’s the result of bilirubin building up before their newborn livers kick into action.
Greer and Raizes guessed that the New Guinean lizards have green innards because of biliverdin, and Austin confirmed their hunch much later. The lizards’ blood contains so much of the green pigment that it completely overshadows the normal red of their hemoglobin.
A tube containing some of the lizards’ blood. (Christopher Austin)
They should be dead. Biliverdin can damage DNA, kill cells, and destroy neurons. And yet, the lizards have the highest levels of biliverdin ever seen in an animal. Their blood contains up to 20 times more of it than the highest concentration ever recorded in a human—an