That's an interesting question... it seems to me it's not new for human beings to find alternatives to breastfeeding babies for numerous reasons (we used to have a much higher mother mortality rate in the early mod period and before), whether that is a wetnurse or other kinds of milk or milk based products. Might have something to do with it? Especially since animals like mice tend to have higher numbers of babies at one time and over the course of their natural lives--they have higher numbers to account for higher mortality amongst their litters... We are more likely to have one at a time, and space out pregnancies over the course of our reproductive lives... Maybe because of that there is more... I don't know the word... failsafes?... built into that system of creating antibodies (and probably other systems).
Does that sound vaguely science-y?
Our "litters" are too small for the survival of our species without lots of safety nets built in. Here's the best way, but if that doesn't work, there are a number of back-ups to deploy.
In addition, I wonder if there might not be an IBS vs. IBD (identical by state rather than by descent) issue, in that for most of human history, whoever substituted their milk (in the case of wet nurses, which would be the most common solution) would have been from the same ethnic stock and locality. It's not like a baby who cannot breastfeed from Mom in a Bantu tribe will magically get milk from a woman in Quebec instead.
I would suggest that breast feeding, gut inoculation, and antibodies are not absolute requirements, but rather a way to load the dice for survival. Babies are living creatures with pretty good homeostatic systems. But they are at a delicate and unstable stage. Many survive even if given modest nutrition. They will make due with unbalanced diet, random gut flora, and untrained immune system. But if moms can bias the odds by tweaking the nutrition, giving a few safe stains of bacteria, and moderating gut flora with antibodies, the results should be healthier kids more often. Not always, more more often.
What is interesting is that if the antibody is useful, why isn't it produced by the baby? Babies can't supply their own nutrition and have to live in the microbiological environment they are born into. But if the mom is producing a critical antibody, those genes must exist in the kid for them to use. So why aren't they?
1 The antibody is more useful in the alimentary tract, maybe even in the upper tract. And detrimental when systemic in the body.
2 Training the infant immune system. Mom's system has learned what the environment is like, but the infant system can't tell friend from foe. Antibodies in breast milk might be a way for mom's to pass on what they have learned by marking bacteria in the baby as friend or foe, which is then inspected by the infant's immune system for creating a new friend / foe list. Basically giving the kid a head start by passing on immunological learning in a non-genetic way.
Just thinking out loud.
This is just a conjecture, but as a person with digestive auto-immune disease I suppose it is my right to guess :
1. No human milk, only formula
2. Life in the 1970's and all the space age chemicals and soluble plastics suddenly injected into the food supply
3. Massive doses of IV antibiotics in response to an infection in my 20s which surely damaged my micro-biome.
all added up to Crohn's disease.
Without it, young mice face long-lasting consequences, including several signs of inflammatory bowel diseases (IBD).
The first level popular press article does not say that they develop symptoms reliably, just signs. Which could mean clinical measurements which are associated with IBD rather than symptoms. If you read the abstract this appears to be the case. Patterns of gene expression, microbial populations, etc. Not sure they looked at actual disease at all. Hard to ask a mouse if it has a stomach ache.
A further possibility is that it may well not be 100% in the mice. Would have to read the whole article, which isn't trivially available... sadly.
Another is that the symptoms are much more reliable in the strain of extremely inbred lab mice they used (all lab mice are extremely inbred). Wild mice or humans may be more robust via diversity.
Another is that the very uniform prison like environment lab mice live in makes the outcome more reliable. Non-breastfed human children are likely encountering the gut bacteria of lots of other humans. These mice are likely only encountering their mother, and may even be separated from her early. Would have to read the paper.
I think the hypothesis on why infant immune systems aren't fully active immediately is that it is going through some initialization steps where it learns to ignore self and constant environmental factors. It cannot do that and simultaneously react to threats, so the mother's milk supplies a stream of antibodies which ought to be good against whatever diseases are floating around (because the mother already had them, or gets them along with the child). However it is also entirely possible that it doesn't turn on earlier mainly because it was never a problem until quite recently. Any baby that did not get breast fed was almost certain to die anyway.
That sounds pretty plausible to me. It's rarely just a singular cause, but multi-causal...
There's also the idea that newborns develop their microbiome through a variety of exposures -- breast milk being one of them. For example, I've read that vaginal birth can add to the diversity of an infant's microbiome (and I'm going to go out on a limb and assume that the mice in question were not removed via c-sections). Likewise general exposure to "dirt" exposes one to a host of bacteria, both good and bad.
As several commentators have noted, it's unlikely that there is one magic bullet for health. While one might argue from demographic studies that the historical preponderance of formula feeding in certain populations might be connected to a statistical increase in certain health problems, it is obvious that the vast majority of people raised without breast milk managed to develop well enough (ie without any pathologies developing as a result).
A whole bunch of mice with Irritable Bowel Diseases, that sounds like fun. I'm picturing a scientist with lab coat and clipboard staring into a mouse cage. Suddenly clear visual evidence of IBS is spewed all over the side of cage. The scientist makes a check mark on his clipboard and moves on.
So what do adults with IBS do now? Find a lactating woman to help out? That's going to be a weird craigslist ad.
Please note - IBS and IBD are two different things.
This article discusses IBD not IBS.
It has been a few years, but I used to study the immune development of infants. Milk sIgA slows the development of the infant's gut immune system giving it more time to entrain to the environment and mature properly. An infant without milk sIgA (i.e. formula-fed) has a gut immune system that has to mature much more rapidly with fewer developmental milestones completed in immunological maturation. This provides more opportunities for abnormalities to develop (i.e. not deleting self-reactive cells properly), but the immune system has a fair number of redundancies to prevent it from happening often.
Fecal transplants seem to be the rage. Though it would be an interesting discovery if breast milk were an alternative to that.
Somehow, it had to come to fecal transplants!
I did not need to think about that. Just seeing it in print here is enough to be aware that somewhere, out there, is a fetish site devoted to this. I'll just nope to that. Good job! I'm not easily squicked.
There's a thriving market in human breastmilk, just as there is one in raw cow milk. Both are delicious!
Er, or that's what I've heard, oh, yeah, totally, that's what I heard other people say. Yeah.
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