Neonatal jaundice and just so stories

Newborn child baby having a treatment for jaundice under ultraviolet light in incubator.

Writing on The Conversation, three UK scientists make an elementary error.

Their piece is entitled Jaundice in newborns could be an evolutionary safeguard against death from sepsis.

In newborn babies, jaundice is so common as to be termed physiological. It affects around 60% of term babies and around 80% of preterm babies in the first week of their lives. Clinicians need to monitor it carefully and sometimes treat it, since it can lead to conditions like acute bilirubin encephalopathy and kernicterus that can damage the infant’s brain and cause developmental problems.

But it now looks as though this jaundice is not merely one of the pitfalls of entering the world. New research just published in Scientific Reports, in which we have been involved, suggests that it is one of the gifts of evolution. Humans may develop jaundice as newborns to protect from something even more serious: sepsis.

The elementary mistake is invoking the the naturalistic fallacy, a logical fallacy that presumes that anything that exists in nature must be good.

[pullquote align=”right” cite=”” link=”” color=”” class=”” size=””]How would we determine if jaundice prevents sepsis? We would look at the relatively risk of sepsis in jaundiced babies vs. non-jaundiced babies.[/pullquote]

…[W]hy have humans not evolved to overcome this temporary bilirubin problem?

Why? Because evolution through natural selection does not produce perfection. A variety of often conflicting evolutionary pressures may result in a relatively high wastage rate.

For example, in nature many babies and mothers die because the baby is too big to pass through the maternal pelvis. The evolutionary pressure on maternal pelvis size is entirely independent of the evolutionary pressure on fetal head size. If natural selection produced perfection, human beings would have evolved some way for the mother’s body to communicate with the fetus’ body to constrain its size. That has not happened because natural selection is limited in what it can accomplish; it can only produce limited results with existing genetic material.

Moreover, evolution through natural selection leads to the survival of the fittest, NOT the survival of all. The fact that a given natural process has a relatively high death rate is entirely in keeping with that principle.

There is no evidence I’m aware of that shows that neonatal jaundice is beneficial in any way to a baby, but that hasn’t stopped these investigators from fantasizing otherwise.

One night he was looking after a baby boy who had sepsis, which is where the immune system goes into overdrive to protect against infection, potentially leading to severe inflammation, organ failure and death. This baby was profoundly unwell in intensive care, suffering from inflammation and a strikingly high bilirubin count that was only just being controlled with three phototherapy lamps. Usually this kind of difficult jaundice is caused by an immune reaction between mum’s and baby’s blood groups, but not in this case.

Richard began wondering if the bilirubin was directly linked to the infection, and if it was part of the baby’s body’s attempt to clear the sepsis (in this case the baby survived). He started thinking about the problem in evolutionary terms – if jaundice can harm the baby, what benefit does it offer to balance this?

The odds are high that the bilirubin is linked to the infection but not in the way that the investigators imagine. Sepsis can injure the liver, decreasing its ability to metabolize bilirubin. Sepsis induced jaundice occurs at all ages.

According to Clinical review: The liver in sepsis:

During sepsis, the liver plays a key role. It is implicated in the host response, participating in the clearance of the infectious agents/products. Sepsis also induces liver damage through hemodynamic alterations or through direct or indirect assault on the hepatocytes or through both. Accordingly, liver dysfunction induced by sepsis is recognized as one of the components that contribute to the severity of the disease.

In other words, there is no reason to believe that neonatal jaundice is protective against sepsis and no data that shows that neonatal jaundice prevents sepsis. No matter.

The results of this project have just been published. Our team have shown that even modest concentrations of bilirubin reduced by one third the growth of Gram-positive Streptococcus agalactiae. We also showed that bilirubin may alter substrate metabolism in the bacteria.

In short, it looks like the hypothesis is bearing out. We now need to do more work, probably in animal experiments of sepsis. This will enable us to think about whether clinicians should raise the accepted bilirubin threshold for babies at risk of sepsis – those born prematurely, for example.

No, it does NOT look like the hypothesis is bearing out.

That bilirubin kills some common bacteria is not unexpected. The whole problem with jaundice in the newborn is that bilirubin is cytotoxic; if it could kill newborn brain cells, it’s hardly surprising that it can kill bacteria, too. That doesn’t mean that excess bilirubin occurs to prevent bacterial sepsis.

Sadly, this is a “just so story.”

What’s a just so story? The term comes from a Rudyard Kipling book of the same name, filled with stories like “How the leopard got its spots.” It is:

an unverifiable narrative explanation for … a biological trait … The pejorative nature of the expression is an implicit criticism that reminds the hearer of the essentially fictional and unprovable nature of such an explanation.

This story could be titled “how the infant got its jaundice.”

Kipling’s just so stories were fairytales and most contemporary efforts to use just so stories to explain evolutionary phenomena are also fairytales.

As Steven J. Gould wrote:

…unfortunately a very large part of evolutionary theory and practice, natural selection has operated like the fundamentalist’s God–he who maketh all things… When evolutionists try to explain form and behavior, they also tell just-so stories–and the agent is natural selection.

But natural selection is not the only engine of evolution.

…[W]e now reject this rigid version of natural selection and grant a major role to other evolutionary agents (genetic drift, fixation of neutral mutations, for example). We must also recognise that many features arise indirectly as developmental consequences of other features direct subject to natural selection. Moreover, and perhaps most importantly, there are a multiple of potential selective explanations for each feature. There is no such thing in nature as a self-evident and unambiguous story.

How would we determine if jaundice prevents sepsis? We would look at the relatively risk of sepsis in jaundiced babies vs. non-jaundiced babies. Unless and until we can show that jaundice is protective, we have no business asserting that it is protective. We also have no business extrapolating from test tubes to human beings. No doubt bleach also kills the bacteria that cause neonatal sepsis, but that’s not a reason to start giving sick babies bleach.

The authors conclude:

It feels like we’re discovering something new about the physiology of newborn babies. It’s the excitement of being a clinician scientist: taking an idea from a real patient into the laboratory and testing then developing it to hopefully help future patients. When newborn babies develop jaundice in future, we’ll still need to treat it carefully. But quite possibly we will also be thankful that it’s protecting them from something potentially life-threatening.

No one has discovered anything about the physiology of newborn babies because no one looked at the physiology of newborn babies. They made up a just so story.

Just so stories are remarkably attractive; that’s why scientists must be very careful not to invoke them. They should be even more cautious about advancing therapeutic recommendations based on what at the moment is little more than wishful thinking.

12 Responses to “Neonatal jaundice and just so stories”

  1. Sue
    June 1, 2018 at 1:27 am #

    Naturalistic fallacies are even more ironic when shared on the internet.

  2. yentavegan
    May 31, 2018 at 7:53 am #

    But if we only can explain away the natural occurrence of jaundice as a positive adaptation or a benign anomaly…why jaundice is nothing at all, nothing to see here

  3. May 29, 2018 at 3:37 pm #

    Well, nature has patched together a bunch of semi-solutions to lots of problems for humans – but that’s a different thing from deciding it’s the best solution available now.

    To use an obvious example, genetic malaria resistance in humans comes from a variety of hemoglobin chains that react sub-optimally in certain solutions and often fatally for people who carry double recessives.

    I think most people would prefer access to trained mosquito access control technicians, insecticides, bed nets, window screens, air conditioning and pharmaceutical treatments over the natural options.

  4. demodocus
    May 29, 2018 at 12:43 pm #

    I think Newman suggested something along those lines in that breastfeeding book I was loaned. Not sure; it’s been 4 years since I read it.

    Anyway, why would jaundice be a good thing in one age group when it’s a bad sign for anyone older than a neonate? Is there anything else that’s good in 4 day old that’s bad in a 4 week old? I mean, wth do I know, but it sounds weird to me.

  5. Roadstergal
    May 29, 2018 at 12:43 pm #

    Lactivists using this non-study to downplay EBF-associated jaundice in 3… 2… 1…

    • yentavegan
      May 31, 2018 at 12:34 pm #

      Jaundice has been downplayed for 30 years in lactivists circles. I fight an uphill battle encouraging mothers to listen to what the pediatrician says rather than crowdsource from a bunch of clucking hens. I nearly got myself booted from a facebook page for recommending a mother follow the doctor’s orders to temporarily stop breastfeeding, supplement with formula to see if the jaundice clears.

  6. Cartman36
    May 29, 2018 at 10:27 am #

    OT, I had been waiting for a copy of Babara Ehrenreich’s book “Natural Causes: An Epidemic of Wellness, the Certainty of Dying, and Killing Ourselves to Live Longer” from the library. I got it but didnt make it past the first chapter when she began to bemoan the c-section rate and other birth interventions without discussing that c-sections have literally saved millions of lives. Apparently, unnatural = bad, who cares how many babies have survived thanks to c-sections. Its going back to the library unfinished today.

    • May 29, 2018 at 2:10 pm #

      The only Barbara Ehrenreich book I read was “Nickled and Dimed”. I do appreciate what she was trying to do in terms of raising awareness of how impossible it is to live on minimum wage, the book was filled with moments that made me cringe as someone who lived in the blue-collar neighborhood and worked at some of the jobs she did.

      Her decision to leave off her Ph.D because she thought it would raise questions at Walmart was delightfully naive. If anyone questioned it, the words “I just got divorced and need to keep a roof over my family’s head” or “I haven’t been able to work in my field since I returned as a medic in a war zone” or “We’ve had cutbacks at my job” worked just fine for the people I worked alongside with advanced degrees.

      It would be lovely to purchase work clothes at the store you work at – but most of us bought the first round of work clothes at Goodwill or Salvation Army. Heck, you can often find extra uniform shirts for the major retailers and restaurant chains that have been donated by people who got out.

      Living without a roommate is an ideal for many middle-class people – but single adults generally split houses or apartments. There’s an entirely new level of abrasiveness involved – but it saves a lot of cash and potentially a lot of energy if people get along and split chores.

      It’s been over 10 years since I read it. I appreciate what she was trying to do…but the book left me with a bad taste in my mouth because it was clear she didn’t take the time to get to know working class families – and the tricks they use to survive before leaving the ivory tower.

      • Cartman36
        May 29, 2018 at 2:48 pm #

        I read nickel and dimed as well and I definitely had the same taste in my mouth as you. I told my husband it reminded me of the documentary I saw with a middle class vegan chef doing the food stamp challenge where she bought organic butter because she felt it was SO much better. I’m sorry, but people who are really struggling often don’t have the luxury of buying organic. Nickel and Dimed came across the same way, a privileged person trying to pretend they “get” poverty.

  7. CanDoc
    May 29, 2018 at 9:09 am #

    Bizarrely, their “pop culture” piece in The Conversation is a bit of a departure from their academically more rigorous published research in Nature, in which the authors counsel “It may be that hyperbilirubinemia in this context reflects an innate immune response rather than an epiphenomenon, a concept that warrants further exploration, however we should also remain mindful that the level of hyperbilirubinaemia appears itself to be an independent prognostic indicator in severe sepsis.” (

    The original research is interesting: Could a very small degree of jaundice be protective?

    The pop culture piece, not so much: RAH RAH JAUNDICE WILL SAVE YOUR BABY FROM SEPSIS!

Leave a Reply

You must be logged in to post a comment.