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Apparently these lizards have loads of Biliverdin in their blood making their blood green! Besides a defense against parasites I figure this is also an effective defense against predators.

I would love to inject this trait into my world's creature(s).

  1. Does anyone know what the drawbacks to having this kind of blood would be?
  2. Could a humanoid possess this trait without encumbrance? The article is vague and mentions nothing about what adaptations the lizard went through to have this kind of blood. I have a hunch that I can't back-up that this may affect hemoglobin and thus affect oxygen efficiency.

  3. Also Biliverdin is toxic to us but I'm not sure what exactly it kills in us. Perhapse if that killing vector was sealed... all good?

  4. If this just isn't practical in a humanoid, are there any other defensive blood traits I could use? I've thought of xenomorphs acid blood that just didn't seem practical. Thank you!

Edit Duplicate Question: Doesn't have anything to do with "Other blood colors". I'm asking about bile blood's potential physiological drawbacks (since nearly everything in biology is a trade) and the possibility of other blood-born defense mechanisms. The fact that the blood is green is just a side-note.

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    $\begingroup$ @Secespitus It's not a duplicate. This question isn't asking how to make a creature have green blood. It's asking about how a creature could use its blood as a defense mechanism. $\endgroup$
    – AngelPray
    Commented Sep 13, 2017 at 17:17
  • $\begingroup$ On review while Angel's right and this isn't actually a duplicate it is very difficult to know what you're actually driving at, it is very unclear what you're actually asking for. $\endgroup$
    – Ash
    Commented Sep 13, 2017 at 17:44
  • $\begingroup$ @Ash Are the questions clear now or does it still seem vague? I'm new here, any tips on improving the clarity of my question are appreciated. $\endgroup$
    – Roshiron
    Commented Sep 14, 2017 at 0:04

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It is funny you should bring up the prospect of high levels of biliverdin. I mooted that prospect in this question just a few days ago. Little Green EARTH Men?

As far as I can tell biliverdin is not toxic. Even bilirubin is not super toxic - people tolerate chronic low levels well. People who are sick with yellow or green jaundice are sick because of the liver dysfunction, not the bilirubin / biliverdin itself. Very high levels make you itchy and can cause kernicterus in newborns. As you note your lizards and some other vertebrates have high levels of biliverdin in the blood. It may act as a free radical scavenger.

It occurred to me that a group of people who underwent evolutionary selection for very pale skin might derive benefit for high biliverdin levels as regards protection from UV light. Although they would then be green, which might make it hard to get a date. And also, circumstances (cold weather / short days) favoring very pale skin also favor lots of clothes.

But high biliverdin: yes, definitely. I was not able to find any pictures of people with green jaundice from his biliverdin. I did find these pictures of milk, serum and urine from a case report of two ladies with mutations that caused accumulation of biliverdin during episodes of liver trouble (but apparently not at baseline). Interestingly both ladies were Greenland Inuit.

Nytofte et al J Med Genet. 2011 Apr;48(4):219-25. A homozygous nonsense mutation (c.214C->A) in the biliverdin reductase alpha gene (BLVRA) results in accumulation of biliverdin during episodes of cholestasis

enter image description here

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  • $\begingroup$ The article clearly states that biliverdin is toxic in humans but I can't find anything else on the internet that backs him up, leading me to believe that the article may have misquoted him. Thank you for this clarification Will, it's disheartening but appreciated. $\endgroup$
    – Roshiron
    Commented Sep 14, 2017 at 0:09
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    $\begingroup$ Do you mean /But if excess bilirubin or biliverdin in the bloodstream goes untreated, it can be deadly./? I think the author means that the appearance of that signals a serious problem with the liver, which is failing. It is not the bile pigments themselves but other more important jobs the liver does that wind up being lethal. $\endgroup$
    – Willk
    Commented Sep 14, 2017 at 0:38
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    $\begingroup$ Nope, that's not what I meant. Here are two quotes from the article: "The remaining mystery, Austin says, is that biliverdin is extremely toxic." --- Right after that quote it says that if a tiny amount is found it indicates jaundice, so you could say the article misrepresented that, but right after it says: --- "Austin believes that the presence of toxic biliverdin instead of hemoglobin may make it harder for Plasmodium to infect the skinks." There it clearly states it's toxic. STILL, I can't find any other source that states it's toxic, so I think the journalist might be off. $\endgroup$
    – Roshiron
    Commented Sep 14, 2017 at 14:45
  • $\begingroup$ “ biliverdin levels as regards protection from UV light.” I am interested in this statement for a story I’m writing but I googled this and can’t seem to find more details on UV light protect and Biliverdin. Does anyone have more detail or a source for this? $\endgroup$
    – Myisha
    Commented Nov 1, 2020 at 16:21
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    $\begingroup$ @Myisha - you can get started here pubmed.ncbi.nlm.nih.gov/25689514 and here sciencedirect.com/science/article/pii/… $\endgroup$
    – Willk
    Commented Nov 1, 2020 at 18:40
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If you're running a reasonably science-based world, with fairly robust evolutionary processes, you can figure that most of the creatures are going to wind up pretty well-tuned evolutionarily. Evolution is really good at tuning and tweaking. At that level, then, all things are tradeoffs. If you have blood that is tuned for being toxic, then it's likely going to lose something in carrying oxygen, immune system, or whatever. Likewise, you're going to have to make the rest of your body able to function in a stew of the stuff, which means biochemical alterations (with their own costs).

Now, this is probably not worth it for a sapient species overall. Special-use answers like this generally won't be. Sapience offers an answer that is at least as good as poison blood, and has a notable metabolic cost of its own. Unless there was some driver actively forcing them to remain that way, their blood would likely become less billious over time after a sufficient level of sentience had been achieved.

...of course, there are all sorts of ways to justify it. In particular, if someone else is uplifting these creatures... well, humanity makes a lot of compromises to things like calorie-efficiency that we don't really need as much anymore (or at least, not in the developed world). Alternately, if they had some strong continuing reason to need that sort of blood even after they got intellect, it could still be maintained naturally. It's just that justifying it is going to take a bit of work.

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  • $\begingroup$ I've got the justification in place, it's just the drawbacks I'm concerned about. What kind of costs would these biochemical alterations necessitate? Just eating more? $\endgroup$
    – Roshiron
    Commented Sep 13, 2017 at 15:46
  • $\begingroup$ So wait, do you mean "sentient" or "sapient"? Those words convey very different things, and it almost feels like you may have them confused. $\endgroup$
    – Pleiades
    Commented Sep 13, 2017 at 16:05
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    $\begingroup$ @Pleiades - fixed. For the drawbacks, you might have thigns like eating more (which is a pretty heavy cost, as evolutionary things go), moving slower, less robust immune system, and similar things. $\endgroup$
    – Ben Barden
    Commented Sep 13, 2017 at 16:50
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As far as I can tell, biliverdin is only toxic in very high levels. It's a byproduct of breaking down heme, and will usually break down into bilirubin unless it has been oxidized. I would guess that either you would need more oxygen to maintain the biliverdin,a higher red blood cell count, or modifications to the liver itself.

As to why it's toxic in high levels, Kernicterus is a form of brain damage caused by high levels of bilirubin accumulating in the grey matter. According to the Wikipedia article (https://en.m.wikipedia.org/wiki/Kernicterus) this is commonly seen in infants, possibly because of the less developed blood-brain barrier. It could likely be circumvented by preventing the breaking down of biliverdin to bilirubin in the bloodstream, or by strengthening the blood-brain barrier.

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