Quote from Wikipedia
If the above is true, then over time humans may have accumulated beneficial bacteria and eliminated non-beneficial ones. Is there any evidence that this happened ?
Well, the non beneficial ones eventually kill you… Either immediately, or via dysentery and dehydration, or due to stress of poor health. So they are quickly eliminated from the system. As anyone with a new baby can say, it takes a little while for a newborn to pick up the beneficial gut flora from contact with others, and start to produce aromatic versions of number two.
Cite please ? From what I have read, babies “inherit” the flora from their mom
What exactly are you questioning? That the bacteria exist as described or the means by which they got there?
I am questioning the bolded part :
[QUOTE=md2000]
newborn to pick up the beneficial gut flora from contact with others
[/QUOTE]
You were questioning md2000’s response in the OP?
To avoid confusing those of us who aren’t timelords, could you please not comment on our posts before we’ve made them.
Babies “inherit” mother’s gut (and other) bacteria by exposure to them during and after birth. The sort of food the child is exposed to and other exposures help determine what particular microbiota establishes along time. Bacteria are also picked up from sources other than the mother.
There is a large body of research elucidating how our gut microbiota contributes to our functioning and what controls its composition.
This NYT article may contain an introduction to some of the specifics you are looking for.
Here’s a partial transcript of yesterday’s Fresh Air show on this very topic. At the bottom of the page is a link to a chapter of Dr Blaser’s book.
As I understand it Caesarian section can inhibit proper gut flora in the offspring because in a natural birth the woman is expected to excrete at the same time as giving birth, so as to infect the child. By shitting on the baby’s face, that is.
Where do you get that from?
And how, exactly, do you think that happens? Are you picturing that somehow, the bacteria from mom’s guts get into the mom’s bloodstream, cross the placenta into the baby’s bloodstream, and from there work their way into the baby’s intestine? Because that very much does not happen. If it did, massive death would be a problem.
In a sense they inherit from mom. They are exposed to the flora of the vagina. A child born by Caesarian is exposed only to her skin and picks up skin bacteria (into the gut) first.
Hospitals understand the tendency of the emerging baby’s head to squeeze any fecal matter out of the end of the mother’s colon ahead of it. There’s only so much room in the pelvic opening, so it’s kind of like pushing on a tube of toothpaste.
Doctors don’t really like it, though, so unless you’re extremely close to giving birth when you arrive at the hospital, they’ll give you an enema to clear things out. Even if things happen “naturally”, labor gives you plenty of time to clear things out. And even if you neither have an enema nor clear things out naturally, it’s coming out ahead of the baby, in a slightly different location, and the medical staff know how to keep things separate.
Babies are probably exposed to bacteria from the anus that are in the general area. But they don’t typically get smeared with shit.
Just as a minor point, in my (and most parents’ I know) experience, baby number two gets aromatic when things besides milk get introduced, usually half a year or more down the line from birth. Not sure beneficial gut flora has anything to do with it.
Anyway, I think the OP is a little too vague. In evolution, it really helps to be carefully precise.
I *think * the OP’s question is “If this is true, then over time, human populations may have (either after splitting into the current species or before) accumulated genetic changes that result in their guts being more hospitable to beneficial bacteria and less hospitable to non-beneficial (acknowledging that which bacteria are beneficial depends on the circumstances). Is there any evidence that this has happened?”
I’m no expert, but I think it’s accepted that, for instance, diarrhea, is an evolved response to the gut having too much harmful bacteria. Pretty sure it evolved well before humans or even primates split off from ancestral mammals, but would certainly give a “Yes” to the OP.
Not from what I read.
I also think that the quote in the OP is too general to have much meaning. Humans pick up specific flora from their environment and food. Certain species definitely have beneficial outcomes - some produce vitamin B12 or break down undigested lactose, e.g. They can thrive in our guts, which is a warm, moist source of plentiful food. The key word in that cite is mutualistic, which just means mutually benefiting. That does not at all imply that not-beneficial ones are excluded. That obviously has not happened and there is no reason to go from the cite to the OP’s conclusion.
Exapno I am not so sure though that that does not count as inheriting. Clearly most of an infant’s biome is from the infant’s mother and clearly we have co-evolved with our microbiomes over many many generations along with our microbiome also adapting in fairly short periods of time to the circumstances we present it with (high fiber or high fat, so on).
The result of that co-evolutionary process is that we provide our bacteria with the raw material it needs and a home, and they help produce energy for us from substances we cannot digest on our own and produce compounds critical to the regulation of metabolism, inflammation, and a host of other functions. We also create an environment that helps keep them in their place and that foster particular mixes of organisms that work together well - selecting for functional ecologies more than individual beneficial organisms.
One small example of that process: breast milk contains high amounts of this stuff called oligosaccharides. Babies cannot digest it. So what the heck is it doing there? It’s the preferred feedstock to the sorts of bacteria that benefit us long term, that’s what. We are evolved to give certain populations of bacteria what they need to thrive. And they in turn work in concert with each other, some existing off of the H2 that others produce.
BTW enemas are NOT standard before delivery. Decades ago maybe … and then on the belief that getting the poop out of the way ahead of time would make the delivery easier. And some while poop does sometimes happen during deivery it is not what happens most often. But as noted, poop is not required: the vaginal canal is far from sterile.
That was a good cite, and it explained the flora very well. Would you please explain why you think that the mom is not the significant contributor to the baby’s gut flora ? The article seems to say as much.
I am trying to understand this. I’d think the immune system will attack the non-beneficial bacteria and I asked the question if we have evolved to make the beneficial bacteria’s environment in the gut more hospitable ?
Agreed - what I am asking is if the degree of warmthness (temperature) and degree of moistness evolved to support the beneficial bacteria and hinder the non-beneficial ones ?
Not so much warmth and moistness … most bacteria thrive in that warmth and moistness … but other aspects. The established healthy ecosystem itself produces stuff to keep out pathogens like Salmonella. The mucin we produce feeds some. And some of those mucin loving bacteria “talk” to intestinal cells in ways that control obesity, decrease insulin resistance, decrease inflammation, and so on. Moreover one of the best ways to increase those mucin loving bacteria is by feeding not them, but other bacteria in the gut that love those previously mentioned oligosaccharides (the mucin loving ones don’t eat that themselves but supplementing a diet with certain oligosaccharides still get the mucin ones to thrive). So on. If you you really want to get into the weeds on this you can read [this article](file:///Users/gabeseidman/Downloads/9783642257155-c1.pdf) (pdf), especially the sections under the “The Intestinal Microbiome during Health” heading. Our preferred gut ecologies crowd out pathogens, produce stuff that kill the unwanted, and share particular molecular patterns that our cells respond to differentially in different portions of the gut helping control what grows where and how well, and conversely causing different effects on the host.
Leaving humanity briefly, look at the cute koalas!:
Specifically, the last two seconds of the video. Koalas: cute, cuddlesome, coprophagous.
I don’t think the immune system plays a role in your digestive tract. This sounds counterintuitive, but your digestive tract is technically an “outside” surface. Think of your body as an elongated donut or a tube. The “gut” is actually just part of your skin, except its tucked inside the surface of the tube.
Actually, there are specific tissues of the immune system associated with the digestive tract: GALT (gut-associated lymphoid tissue) including Tonsils, Adenoids, Peyer’s patches.
The intestine possesses the largest mass of lymphoid tissue in the human body. The gut microflora seems to play a role in training the immune system, experimental animals raised in a sterile environment do not develop a normal immune system