Kids in countries with "rough" conditions have a much higher mortality than kids in the developed world. I think it's pretty well accepted that the hygiene revolution decreased child (and adult) mortality a lot. That's not to say it didn't create other problems, but surely on net a "cleaner" world is better. Nobody is advocating not washing your hands before you eat.
So while "tougher raised" kids probably have a better immune system, the risk associated with pathogen exposure grow even more dramatically, such that they surpass the benefit.
Concerning kids exposed to those pathogens in the developing world, we have to consider that malnutrition is a major contributor.
The concept only goes so far, and people need to be wary of it being used to potentially justify that harsh living conditions are okay or "better". It can come off as an appeal to nature.
You also may just have chronic re-exposure or a failure to clear pathogens, which can be detrimental to an entire population. An example would be worms that don't get cleared by the immune system and for which the person is constantly being re-exposed to. You end up with cognitive and physical issues that don't kill, but reduce a person's quality of life.
Some of the hygiene hypothesis is around the immune system amping up its response due to parasites, and without the parasites present to attack it turns against the body itself. This is kind of what I am talking about. The people with amped up immune systems possibly handled parasite infections better when they were a common problem, but in a society where most people no longer live with chronic parasite infections, it manifests as allergies/immune disease. Living with chronic parasite infection is certainly not on the top of anyone's list to do, though helminthic therapy is something some people have tried to fix their allergy issues.
It is also incredibly hard to determine who has truly lived a "pure" lifestyle free from interference of modern conveniences, so that evolution can truly be the driving factor in their life. Civilization has disrupted evolution for millennia by now, we can't just look back a few generations and claim they were a "tougher breed" who were better because of their purer natural lifestyle.
Maybe, but
1) the younger you are, the better you can deal with a lot of these infections, it's when you're older and you haven't seen them that they become a problem, and
2) the kind of exposure you get from being filthy is not going to be as concentrated as most of the exposures that make you sick e.g. from other people. A tiny exposure from a bit of dirt is going to take forever to grow into something that will hurt you, so your immune system has plenty of time to figure it out before it gets there. Then when somebody sneezes in your face, you've had the immunity without ever being aware of the sickness.
Here is the CDC saying it:
> Before the 18th century, polioviruses probably circulated widely. Initial infections with at least one type probably occurred in early infancy, when transplacentally acquired maternal antibodies were high and protected infants from infection-causing paralysis.
> In the immediate prevaccine era, during the first half of the 20th century, improved sanitation resulted in less frequent exposure and increased the age of primary infection, resulting in large epidemics with high numbers of deaths. The incidence dramatically decreased after the introduction of inactivated polio vaccine (IPV) in 1955 and continued to decline following oral polio vaccine (OPV) introduction in 1961. From the more than 21,000 paralytic cases reported in 1952, only 2,525 cases were reported in 1960 and 61 cases in 1965.
> Poliovirus Secular Trends in the United Status:
> * Before the 18th century, polioviruses probably circulated widely
> * In immediate prevaccine era, improved sanitation resulted in less frequent exposure and increased age of primary infection, resulting in large epidemics with high death count
> * Incidence dramatically decreased following inactivated polio vaccine (IPV) introduction in 1955
My guess is that sanitary conditions during infancy were still a net positive overall. Just not with respect to polio specifically. To protect children from polio you either need vaccination with dead/weak polio, or exposure to polio as an infant when they had protection from maternal antibodies. Either way teaches the immune system to fight polio, but without either of those the risk of polio rises with age. An adult who catches polio is about 10x more likely to die than a child (not infant) who catches it.
It’s hard to find non kooky references, but the notion of environmental poisons in the gut somehow transferring to the lower spinal cord sounds at least plausible.
It's specifically the sanitation of the living condition of infants that had the effect, not the general sanitation level of society. Polio was still circulating through the population outside during this time period, but infants were shielded from it during their short window of protection.
But I did find where I got that from, for whatever it's worth, George Carlin:
> When I was a little boy in New York City in the 1940s, we swam in the Hudson River, and it was filled with raw sewage. OK? We swam in raw sewage — you know, to cool off. And at that time, the big fear was polio. Thousands of kids died from polio every year. But you know something? In my neighborhood, no one ever got polio. No one. Ever. You know why? 'Cause we swam in raw sewage.
(from https://www.businessinsider.com/george-carlin-why-we-need-to...)
[edit]: I do wonder if, because I have no reason to doubt it's true, what being exposed to sewage-infested water did is provide some sort of vaccination, by means of exposure to very low levels - insufficient for infection - of pathogens including polio. After all, that kind of analogue process is what early vaccination was.
[edit 2]: that might still be completely off, I mean, reading about it I understand that at the time, 10x as many children would die by accidents, and 3x from cancer.
How do you suss out the difference between increasing sanitation vs vaccination in a time where sanitation is on an upwards trajectory? Polio is spread from feces. Eventually people stopped drinking contaminated water. full stop.
What rules out the theory that those who survived were born with superior immune systems, or that they were missing traits that would make them susceptible to severe illness?
https://www.youtube.com/watch?v=X29lF43mUlo
Edit: Usually I regret scrolling down to youtube comments, not this time:
> This is not a comedy, this is a TED talk.
great word