Just because we humans have red blood, doesn't mean the same color flows through the veins of all species. Far from it, the animal world bleeds in a veritable rainbow of colors.
Though it might be hard for us to imagine bleeding in any color besides red, scientists have long been aware of the brilliant shades that course through the veins of our animal kingdom. But six species of lizard in New Guinea that not only have green blood, but green bones, tongue and muscles have left researchers scratching their heads.
Generally the color green in combination with blood means poison. In the case of the curious six, which are skinks from the Scincidae family, the reason for the coloration of other body parts seems to be a particularly high level of green bile pigmentation. Enough to kill humans, if it were in our system.
Evolution appears to be the answer as to how it got there. Originally, close relatives of the lizards in question, had red blood, but at a certain point during their development, scientists believe the toxins in their blood created an evolutionary advantage.
They suggest the lizards may have become green bleeders because green bile kills the malaria pathogen, which may have badly infected their ancestors in the dim and distant past.