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Most of the Native Americans in our history were killed by smallpox, measles, etcetera, and this video makes a good case for why: though the Americas had cities of their own, they lacked many options for domesticable animals, hence they did not come into contact with the beasts continuously in poorly-sanitised places, hence there was little opportunity for animal diseases to jump over to humans, hence the Americans never had their own Bubonic Plague and similar poxes.

Let's change some of that. The video leaves some details out and its arguments have been contested, but let's just suppose that for whatever reason (more domesticable animals, denser and less sanitary cities) the Americas are just as disease-ridden as Europe and Asia. It is a second Europe, in essence, but it still developed separately for ten thousand years.

Would diseases still have killed 90% of Americans but few Europeans? I am considering the following possible outcomes:

  • Hardened by their own plagues, the Americans would not lose nearly as many people to European diseases. Europeans would get their own plagues. In effect both sides of the Atlantic would take a hit after first contact, but no cultures are eradicated (except for whatever results from subsequent colonisation, which is out of the scope of this question).
  • Both continents now have deadly plagues that the other continent is vulnerable to. Each side of the Atlantic loses 75%-90% of its respective population.
  • For some reason the loss of life is still asymmetrical.

What's more likely?

The focus is purely on the disease side. I am not interested in how colonisation would go in this scenario (this question already pretty much covers that), the long-term consequences of a different powerbase in an urbanised Iroquois Confederacy, etcetera etcetera. The essential question is: does having plagues of your own make you hardened against plagues from a different continent?


It is safe to say that this has been a very interesting - and extremely confusing - response.

I would still be curious if someone could enlighten me (because frankly the answers all seem to be answering a different question than what I was trying to ask) with simple yes/no answers to the following steps in my reasoning.

  1. Were or weren't Native Americans killed in greater numbers to Old World diseases, measured as the mortality rate for specific diseases, than the people from the Old World with whom that disease originated? Mortality rate does not include those who were already immune and never contracted the disease during a specific outbreak.
  2. If they were, is this difference explained fully and entirely by societal, cultural, environmental differences with the Old World?
  3. If not, is there is in fact a 'hereditary resistance' (however you want to call it) component resultant from the disease having been endemic in a population for centuries? Something biological that makes a person from one population more resistant to a disease than someone from another population, even if they never personally contracted the disease?
  4. If so, is that component broad, a contributor to the base immune system, or is it just as narrow as regular immune system which will not protect against a virus/bacteria only slightly different from one it has encountered?

It's probably pointless, but before I get even more people telling me to pick up a biology textbook, I want to try phrasing it one more different way.

It's not about whether having had one plague makes you immune to the other plague. That's not the case on several counts; first because I'm talking about resistance in general (difference can be tiny), and second because I'm talking about plagues, plural.

Does a population that has had (for centuries) many different plagues fare any better against a new plague than a population that never had any plagues?

Analogy: two children, one raised in a sterile bubble and the other grew up playing in a forest. As adults, both get the common cold (new to both since that virus changes every year): does the one who grew up sterile not suffer far more from that disease than the one who was raised in the woods?*

My question is whether there is an analogous mechanism in to human populations. Yes yes in the macro scale, over multiple generations, we're not really talking about the immune system specifically any more, but I had held it self-evident that populations do have some form of hereditary resistance to specific diseases endemic to them, as evidenced by e.g. measles which has a different mortality rate in Eurasians and Native Americans. Turns out there's strong, conflicting opinions about whether this exists or not.

But to finish my analogy: if you take two populations, and one has suffered and survived many epidemics because it lived in insanitary cities with livestock, whereas the other has largely lived in less urbanised areas, and even in the greatest cities there were less domesticated animals walking around. Is the first population more resistant (by some amount however small) to a fresh disease than the second population?

Back to my scenario: does giving the Native Americans denser cities and more animals give them an edge (however small) in resistance to fresh diseases, after they have been suffering many diseases of their own? Yes or no. That's my question: that is not a theory that I thought up out of thin air and wholeheartedly believe in.

*Yes yes I know very well that the sterile child would not develop any immune system in this scenario: it is only an analogy.

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    $\begingroup$ You might investigate the history of syphilis. $\endgroup$ – chrylis -cautiouslyoptimistic- Oct 13 at 17:55
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    $\begingroup$ Of course it would. None of your details makes any difference… all people, groups, communities and even civilisations have always been vulnerable to any disease strange to them. Take for instance Covid, or go back to Spanish Flu. $\endgroup$ – Robbie Goodwin Oct 13 at 22:12
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    $\begingroup$ I'm going to make a suggestion that if you want to understand how immunity works then asking on biology.stackexchange.com would be the best place. There's a huge number of factors involved with immunity. $\endgroup$ – Aaron Oct 13 at 22:32
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    $\begingroup$ Not a full answer but: if you wanted to engineer this for a story, the one disease that more densely populated Native Americans could have developed a resistance for is actually smallpox. There's evidence that cow pox was present in North America, possibly introduced by the Vikings, but without its ideal spread conditions, died out. If cowpox had been a common childhood disease among native americans, they would have had a much higher resistance to small pox, since the two diseases are closely related. Wouldn't help them with measles, though. $\endgroup$ – FuzzyChef Oct 14 at 22:56
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    $\begingroup$ The easiest way for you to make this scenario work is to posit that the Greenland settlement was much more successful than it actually was, giving Native Americans several centuries of low-frequency contact with medieval Europeans. This would have exposed them to a bunch of European diseases in sporadic outbreaks over a long period of time ... enough to develop some collective resistance. $\endgroup$ – FuzzyChef Oct 14 at 22:59

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In humans, genetic resistance to disease does exist for specific diseases but not in general

I have not seen any studies identifying human genes that make one more resistant to all disease in general. There are plenty of cases where a specific gene causes resistance or susceptibility to a specific disease.

Lets assume that such genes appear due to a mutation in an individual. In that case they spread locally within a population over several generations thereby creating populations of people with resistance to a specific disease.

People with genes for Sickle Cell can be resistant to Malaria.
https://www.cdc.gov/malaria/about/biology/index.html

Genes for Cystic fibrosis appear to cause cholera resistance.
https://pubmed.ncbi.nlm.nih.gov/26527495/

Some people appear to have a genetic resistance to Tuberculosis causing bacteria.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170664/

The NIH has a whole list of other genetic traits that cause disease resistance.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6150079/

Europe wasn't even immune to their own plagues

Its my understanding that plagues in Europe routinely wiped out large sections of the European population. So even the Europeans weren't really that immune to even their own plagues. So we wouldn't expect a more densely populated America to be any different. It wasn't until they learned about proper sanitation that things got better.

Plagues develop according to the living conditions present in the populations they infect. If both continents contain similar living conditions then we would expect that a plague from one continent might spread well on another. But because the plagues developed in isolation, neither side would have immunity. The likely scenario is that plagues would hit both continents hard.

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    $\begingroup$ Thank you very much for the answer! The last couple of answers were all very valuable, but I accepted this one for identifying specifically what I was getting at, providing sources, and setting limitations that I can make some use of. $\endgroup$ – KeizerHarm Oct 15 at 20:27
  • $\begingroup$ You only talk about genetic resistance. but a big part of the immune system is trained during early childhood, so if a virus is prevalent in a population and most of the children get it, they have built up resistance. The more generalized immune system of children is often more able to adapt as seen with covid lately. $\endgroup$ – Daniel Oct 16 at 15:30
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does having plagues of your own make you hardened against plagues from a different continent?

I would answer looking at the fresh case of Covid19. No matter where the virus hit, the local variety of infections doesn't seem to affect how well or bad the population answers.

I would expect the same to apply also in this case.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – L.Dutch - Reinstate Monica Oct 14 at 4:47
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    $\begingroup$ Can you state sources for your claim? I have seen drastically different infection/death rates (for example take inida and usa) and I don´t think science is anywhere clear on that topic so early on ... $\endgroup$ – Daniel Oct 16 at 15:20
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One word: syphilis. Of which the great virulence among Europeans for the first two or three centuries after it came from the Americas shows that it doesn't matter if they had contagious diseases in general, only that they didn't have that particular disease or that class of diseases.

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    $\begingroup$ it's unproven that syphilis was absent in Europe prior to the Columbian exchange. It was treated as a novel disease when there was the outbreak at the end of the 15th century, but it's possible that it had previously been known, but then forgotten, and there are scholars who suggest that there are Ancient Greek descriptions of some stage of the disease $\endgroup$ – Tristan Oct 14 at 12:29
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    $\begingroup$ @Tristan: We know that syphilis existed in the Americas. We know that it emerged as a virulent disease in Europe after contact with the Americas. We also know that the classical world was sexually very active, and that in those times people were not worried about STDs. But, yes, we don't have proof that the novel disease was imported from the Americas. $\endgroup$ – AlexP Oct 14 at 13:33
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    $\begingroup$ To argue that syphilis didn't come over from the Americas is to argue that it was somehow present in Eurasia for possibly milliena, then totally coincidentally had its first ever documented outbreak in Southwestern Europe one year after Columbus' return to Southwestern Europe. All of human history to pick, and and the world's biggest continent to happen in, and it randomly picked that time and place. $\endgroup$ – T.E.D. Oct 14 at 18:43
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    $\begingroup$ @Tristan You're correct. but it takes a bit of time to change a 500-YO opinion, so the current status is "disputed" ;-) $\endgroup$ – Fabby Oct 14 at 19:28
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    $\begingroup$ @Fabby: Using the Daily Mail as your source is not a great idea. Even when they're writing about real studies, they sensationalize them for maximum wow factor, while ignoring the flaws in the study. In this case the study had wildly imprecise radiocarbon dating; the skeletons in question had a possible range of ages from as early as the early-mid-1400s to as late as the early 1600s (so over half the possible range was post-Columbian). It didn't prove a thing. $\endgroup$ – ShadowRanger Oct 15 at 1:29
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Yes. Immune systems aren't the only thing that needs practice dealing with outbreaks.

How good one countries zoonanautic outbreaks inoculated them for an introduced outbreak from another country will be a bit hit and miss. American Cow pox could protect against european smallpox, but maybe some other disease might not be protected. Who knows exactly how the immune systems play out and what new stuff infects Americans in this world.

What will help;

  • Quarintine procedures in force from last outbreak.
  • recognising it's a medical issue and not a religious one.
  • practice at locking down cities.
  • symptom checking incoming people.
  • isolating those who display certain symptoms.
  • Doctors knowing how to treat respiratory problems.
  • First aid training
  • Sanitary lessons from the last plaque.

A case study for this is Asian countries that were hard hit by SARS doing better than expected with covid. An example is Vietnam. (That article is to the latest in a series on what Vietnam is doing against covid, I'd recommend reading all the series).

Singapore also showed some very early promising results as a result of what they learnt from SARS, however their later figures declined as they lost control of workplace dorm infections.

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    $\begingroup$ Er ... but 16th-century Europeans didn't do any of these things. So that's completely irrelevant to how things would have unfolded during the colonial era. $\endgroup$ – FuzzyChef Oct 14 at 22:47
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    $\begingroup$ @FuzzyChef: 16th century Europeans did engage in quarantines/isolation (quarantines have been used for thousands of years), and in some cases locked down whole cities successfully (example from 17th century admittedly). Granted, the rest of the list is very much modern; doctors in the 16th century were generally unaware of effective diagnostic or treatment options for pandemics. $\endgroup$ – ShadowRanger Oct 15 at 1:42
  • $\begingroup$ True. But most of the treatments/measures that Europeans used in the 16th century were maltreatments that, if anything, made the diseases worse. Leeches, arsenic, white lead, sweat treatments, ice baths (for the wrong thing), pomades, etc. Certainly you can't assume that European medicine was doing anything to prevent pandemics on any scale. $\endgroup$ – FuzzyChef Oct 15 at 4:48
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Yes and No...

It is unlikely that the Natives would have a natural herd immunity when dealing with diseases that would have evolved in such isolation, but they would still fare much better. One of the biggest reasons that the Natives lost so many people to European plagues was culture. In Europe where plagues were common, they knew to isolate the sick, burn the bodies, lock down travel etc. Smallpox, for example, was nearly as deadly to Europeans as Americans, but among Indigenous Americans, when a person got sick, it was generally their culture for everyone to come and visit them to take care of them until they got better. If America had had its own history of plagues, then they simply would not have done this as a standard practice; so, even if Europe brought in some really deadly diseases, they would not have been able to spread nearly as much.

You might have still seen a big die off, but probably no worse than the black death which killed 1/3 Europeans in the 14th century rather than the 9/10 that they actually experienced.

That said, even the figures for the black death were only that high because they did not understand that it passed through fleas; so, many normal precautions like masks and social distancing did not work. In all likelihood, the outcomes would have been much less severe than that since Smallpox spreads more like a normal disease (person to person). As for how well Europe would fair... well as it turns out the natives did give Europe a few pretty nasty diseases in exchange. Both syphilis and tuberculosis most likely originated in the Americas. Either one of these diseases could have ravaged Europe nearly as badly as European diseases did to America, but because the Europeans responded to outbreaks better, they never spread to critical levels.

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    $\begingroup$ There were tribes in the Great Plains who looked at other tribes, smitten by, say, measles, and decided their being weakened made them wonderful targets for raids. They also had a practice of wearing dead men's clothes to prove they weren't afraid of ghosts. Culture meant a lot $\endgroup$ – Mary Oct 14 at 1:12
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I don't think it's because it's from different continents. A completely new plague would affect all in the same way unless there is a situation like cowpox and smallpox, where people who have had one cannot contract the other in a severe form.

Measles and suchlike affect populations differently only because of built up resistance.

Measles has been around some areas for a long long time. So it was survived by some who had natural resistance. Their descendants inherited some resistance and there were multiple cycles strengthening this until it's not even deemed life threatening except to an unlucky few in some locales.

In Polynesia, measles all but depopulated some Islands, the survivors resistance carried on in the people today but it's only a couple of generations. So while I'm half European and can consider measles more inconvenient than a danger with a lot of generations of survivors reinforcing the resistance, 85 kids here died of it during the last outbreak and thousands were seriously ill, it's no coincidence that these were almost all full-blooded natives.

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  • $\begingroup$ Maybe I am misreading it but it seems to me that your first paragraph goes against the other three. You say that different populations are affected differently by the same disease because of resistance built up over generations. But one way of separating populations is by putting them on different continents. Any unique American disease would by definition be one that the Europeans had had no hereditary resistance to, and vice versa. So how are continents irrelevant? $\endgroup$ – KeizerHarm Oct 13 at 10:48
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    $\begingroup$ They're irrelevent in terms of time. If a new disease originated in one right now, it would be equally dangerous in the other. But if it originated in one and only moved to the other 1000 years later then there would be a disparity. Because everyone in the first would be descended on both sides from survivors passing down natural resistance and reinforcing it. $\endgroup$ – Kilisi Oct 13 at 10:50
  • $\begingroup$ And that's what I am talking about. I am not conjecturing any brand new diseases; I am conjecturing an alt-history Native American population rife with diseases that they have had for generations. These new diseases would be native to them, but foreign to Europeans, and affect Europeans the way that natives have been affected by European diseases. $\endgroup$ – KeizerHarm Oct 13 at 10:51
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    $\begingroup$ Well, syphilis would be the prime example. And I would think that in that scenario it would indeed work out that way. I don't see how they would be immuno comprimised. Immune to one disease does not help with immunity to others that I know of. The Black death happily wiped out populations impartially who were disease ridden to start with. $\endgroup$ – Kilisi Oct 13 at 10:53
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    $\begingroup$ So that's what I was asking about :) The Black Death is a good example: I know some places randomly were spared, was there no correlation with the overall quality of their immune systems? $\endgroup$ – KeizerHarm Oct 13 at 11:02
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Let's talk about how a plague can wipe out a civilization. Assume a generic disease hits a generic pre-industrial village. It's not even that bad of a disease; everyone will just be knocked out for a couple weeks. It can still kill everyone in the village. Why? Because everyone gets sick at the same time. In this situation, there's nobody who can help treat the sick, nobody to cook, nobody to gather wood for fires, and nobody to draw water, because everyone is sick. (That last one can be the deadliest if the illness includes diarrhea.) If one person from the village at a time got sick, someone else could care for them, and there would be few or even no deaths. Even if only one person happens to be immune, the death rate drops like a rock.

There is no particular reason to say that Europeans have "better" resistance to any diseases, they just had already been exposed enough to European diseases that this particular effect didn't hit them. If Native Americans had livestock kept in the same conditions Europeans had, they would not have been more resistant to European diseases. The only change would be that Europe would probably have caught something nasty from America.

With this in mind:

  1. Were or weren't Native Americans killed in greater numbers to Old World diseases, measured as the mortality rate for specific diseases, than the people from the Old World with whom that disease originated? Yes, mostly because of this factor.
  2. If they were, is this difference explained fully and entirely by societal, cultural, environmental differences with the Old World? No; the difference is because everyone got sick at the same time.
  3. If not, is there is in fact a 'hereditary resistance' (however you want to call it) component resultant from the disease having been endemic in a population for centuries? Something biological that makes a person from one population more resistant to a disease than someone from another population, even if they never personally contracted the disease? No.
  4. If so, is that component broad, a contributor to the base immune system, or is it just as narrow as regular immune system which will not protect against a virus/bacteria only slightly different from one it has encountered? Not relevant.
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Yes

Yes, they would still be vulnerable.

My doctor just admonished me to get this year's flu shot. I've never had one and I've never had the flu. He and I talked about the science literally because too many people think as you do.

Immunity from one disease does not make you in any way immune to a disease your body hasn't encountered before. All it does is protect you from becoming ill from that first disease, which is good, because if you catch it your body's immune system becomes compromised, making it easier to catch another disease.

That is, in fact, how influenzas tend to kill — by compromising the immune system so that another disease (often bacteriological rather than viral) can set in. In the case of influenza, the most common secondary disease (and the one that almost always kills the patient) is pneumonia.

Consequently, where a virus originated is factually irrelevant. Whether or not an individual (an individual, not a geographic location) has been exposed to it is all that matters. When such an individual contracts a disease they've not been exposed to before (any disease, from COVID-19 down to the measles) their body begins developing antibodies. And a race begins. If the body can develop antibodies fast enough, the patient survives and with that new capability becomes fundamentally immune from further infection from that one disease (this isn't 100% true, but statistically it's close enough to 100% that we can leave the details for another day).

The reason diseases like mumps, small pox, measles, etc. have been declared eradicated is because humanity developed vaccines to help individuals build antibodies without having to actually become infected by the disease. So long as enough people are immunized (herd immunity), the whole of society is functionally protected.

The problem with your scenario is that you believe that immunity from one set of diseases grants immunity to another set and, for some reason, you think that geography is involved.

It's not.

The reality is that if the Native Americans had immunity to all sorts of diseases but no immunity to measles, then when the Europeans exposed them to measles, they'd contract it.

However

What all that immunity would do is keep the body from catching those diseases, reducing the liklihood of the body contracting the new diseases. A healthy body can fight a new disease better than an unhealthy body (that should be obvious).

My belief is that the plagues that swept the Native Americans would have still happened. At best, the number of deaths would have dropped. If 90% can be believed, maybe only 70% would have happened.

But they would still happen.


Edit

There is no such thing as a "base immunity." This means there is no combination of diseases which, once survived, produce any level of immunity against another disease. Even influenzas, which one might think are of a "general class" that could create an immunity that protects against new influenzas, don't enjoy this benefit. Each and every disease is a threat to anyone, anywhere, who hasn't been exposed to it.

To reiterate my original answer, the benefit of having been infected by many diseases is that your body will remain healthy, giving it the best chance of survival should it be exposed to a new disease.

There are two ways immunity to a specific disease can be inherited.

(1) A population is infected. Again and again. People die — a lot of them. The survivors have a natural immunity. To intone the indomitable Morgan Freeman from the movie War of the Worlds (2005):

From the moment the invaders arrived, breathed our air, ate, and drank, they were doomed. They were undone, destroyed, after all of man's weapons and devices had failed, by the tiniest creatures that God in His wisdom had put upon this Earth. By the toll of a billion deaths Man had earned his immunity, his right to survive among this planet's infinite organisms. And that right is ours against all challengers, for neither do men live, or die, in vain.

(2) By birth, the antibodies in a survivor mother can be passed to her children. However, this process is imperfect and only temporary because the baby's body has not learned how to build those antibodies.

For example, if the mother has had chickenpox, she'll have developed immunity against the condition and some of the chickenpox antibodies will be passed to the baby.

But if the mother hasn't had chickenpox, the baby won't be protected.

Immunity in newborn babies is only temporary and starts to decrease after the first few weeks or months.

Breast milk also contains antibodies, which means that babies who are breastfed have passive immunity for longer. (Source)

Neither solution guarantees protection from that one disease. They only reduce the likelihood of infection. Regrettably, there are only two ways to actually protect an individual from future infection (no matter who it is and no matter what the disease is):

(a) They can become infected by the disease and survive (their body learns to create its own antibodies).

(b) They can be artificially inoculated with a vaccine (forcing the body to learn how to create antibodies without threatening, or with less threat, to the body).

To reiterate my answer...

Yes, they would still be vulnerable

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  • $\begingroup$ "you believe that immunity from one set of diseases grants immunity to another set and, for some reason, you think that geography is involved". I don't. Please lay off from telling me what I believe in. $\endgroup$ – KeizerHarm Oct 13 at 14:05
  • $\begingroup$ I'm not saying that a person's resistance to the pox depends on one's location on the globe. But different human populations - who in this example live on different continents - have different resistances to diseases, as evidenced by e.g. the hugely different mortality rate of the measles between Native Americans and Africans, and Kilisi's example of different people on one Polynesian island dying at different rates depending on how much European ancestry they had. $\endgroup$ – KeizerHarm Oct 13 at 14:08
  • $\begingroup$ I am asking whether this 'base immunity' carries over to diseases in general. I don't believe it, I am asking it. And you can say that it isn't without going at me like that. $\endgroup$ – KeizerHarm Oct 13 at 14:10
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    $\begingroup$ @KeizerHarm I am with JBH on this one. Your question is worded like you thought that having been affected by a plague somehow magically gives you resistance to completely unrelated plagues EG. "does having plagues of your own make you hardened against plagues from a different continent?" If its the same plague your question still doesn't make sense. $\endgroup$ – IT Alex Oct 13 at 17:57
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    $\begingroup$ Actually, the innate immune system is effective against many invaders, including novel ones which have not been seen before. And apparently, some antibodies are sufficiently general to be effective against novel viruses/bacteria. So I think this answer is overly strict w.r.t. actual immunology. I agree there is no such thing as "base immunity" in a general sense, but there is evidence that exposure to some coronaviruses gives protection against some others, for instance. $\endgroup$ – Lawnmower Man Oct 13 at 21:14
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does having plagues of your own make you hardened against plagues from a different continent?

Not all of them. Possibly some (don't count on it).

That's a bit like asking whether having risked being maimed by lions offers any protection against being maimed by leopards or crocodiles. Obviously it does not.

There is a very tiny possibility that the pathogen from across the sea actually targets some vulnerability that had been independently exploited by a local plague, which wiped out most potential victims. Survivors are now much more resistant to the local plague, and coincidentally immune to the new one.

This happened in humans when the Black Death came to Europe in 1348. The mortality was much higher among those Europeans who had a specific chemokine genetic marker; as a consequence, the survivors that got to reproduce more had, more often than not, the mutated form (dubbed CCR5-delta-32). Five centuries later, a zoonotic virus arose from a different continent, Africa, causing AIDS - and the European mutants turned out to be significantly more resistant.

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    $\begingroup$ Also thank you for this answer! It was a toss-up whether I accept this one or user4574's; went with the one with the lower total reputation by the end :) $\endgroup$ – KeizerHarm Oct 15 at 20:28
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    $\begingroup$ @KeizerHarm good call! :-) $\endgroup$ – LSerni Oct 15 at 21:06
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This is sort of like asking if a nation that had become resistant/immune to cholera would then be resistant/immune to small pox. There is a fairly low limit to the overall resistance an immune system can create, beyond which it develops countermeasures to specific maladies that it had encountered before. It doesn't matter how strong an immune system your body has due to evolution or exposure when you're dealing with an infection that your body has never seen before. (It is able to fend off generic diseases or other invading foreign entities that are either limited in scale or unaggressive in attacking the host cells, but we aren't talking about those.)

The only thing that might have changed with the Native Americans is that they maybe would have had better precautions in place to deal with plague outbreaks, but the contagiousness and severity of the infections themselves would not have been lessened whatsoever.

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If you preserve the asymmetry of travel, with more people travling from Europe to the Americas than the other way, the problem persists. The incubation period for disesases is shorter than the time to cross the Atlantic. Healthy carriers are traveling from Europe to America. Europeans who contract illnesses in the Americas:

  1. Die in America, so do not spread the disease to Europe
  2. Die on board ship, and are buried at sea, so may or may not spread the disease further
  3. Catch the disease on the ship from a dying person and survive to reach Europe

I believe that the magnitude of the disease vectors pointing from Europe to America are much greater than in the other direction. The Americas will be disproportionately affected.

From https://thesouthern.com/progress/section3/searching-for-clues-in-the-disappearance-of-the-mississippians/article_d6c13308-f414-11e0-b052-001cc4c03286.html

When Father Jacques Marquette led an expedition down the Mississippi River in 1673, becoming the first European to penetrate into the Southern Illinois wilderness, his party met with a scene fit for a ghost story.

The group saw massive mounds at intervals within sight of the river obviously built by inhabitants of the region, and yet there was no sign of human life. Marquette had floated into what archaeologists now call the "vacant quarter" of North America. The mound-building Mississippians of Southern Illinois, southeastern Missouri, Tennessee and along the Ohio River into Southern Indiana and Kentucky had suddenly and without warning vanished after 1450.

No one knows what wiped out the Mississippian civilization, but disease is a good bet, and it happened before Columbus arrived. North America started off at a great disadvantage.

(More recent research suggests climate change causing flooding and other problems: https://news.berkeley.edu/2020/01/27/new-study-debunks-myth-of-cahokias-native-american-lost-civilization/ )

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  • $\begingroup$ Valid point, thank you! $\endgroup$ – KeizerHarm Oct 15 at 20:21
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Were or weren't Native Americans killed in greater numbers to Old World diseases, measured as the mortality rate for specific diseases, then the people from the Old World with whom that disease originated? Mortality rate does not include those who were already immune and never contracted the disease during a specific outbreak.

They were. By a lot. To the point where europeans/Americans (as in citizens of the USA) thought North America was some sort of garden paradise because of all the seemingly-random well husbanded land. It wasn't random, the previous owners just died in huge numbers and abandoned many areas. Syphilis et al that were imported from the Americans to Europe were bad and killed boatloads of people, but nowhere near the average fatality rate the Native Americans suffered. Smallpox, on the other hand, is deadly to adults and more importantly spreads rapidly. Europeans survived because they tend to catch it early AND they have immune people to care for the sick. Meanwhile the native americans in any given village essentially all got sick at once and had nobody healthy to look after the sick. So even IF (as some argue) smallpox wasn't really more deadly to native americans, a case that a european would survive with care would kill a native american, because they had no healthy caregivers.

If they were, is this difference explained fully and entirely by societal, cultural, geographical differences with the Old World?

Almost. Syphilis, being an STD, is harder to transmit that, say, smallpox. It also doesn't kill as fast. Same goes (more or less) for the other New World diseases. If tuberculosis transmitted a bit better, or killed quicker, that might have changed the numbers. The delayed-deadliness of New World diseases could be a factor of less cramped livestock co-habitation, but mutations are also somewhat of a crapshoot.

If not, is there is in fact a 'hereditary resistance' (however you want to call it) component resultant from the disease having been endemic in a population for centuries? Something genetic that makes a person from one population more resistant to a disease than someone from another population, even if they never personally contracted the disease?

Yes, but not quite how you may be imagining. For example, Sickle cell anemia (common in people of african descent), is considered bad for a whole host of reasons such as increased risk of stroke, but also gives a genetic advantage against malaria. It's not so much that your resistance to maleria is passed down via some sort of inherited immunity, but your genetics may dispose you to better resist the effects of certain diseases. Which is why Native Africans do just fine in central africa, but white people died their in droves there from malaria. It wasn't that Africans were born with malaria antibodies or had different/better immune systems, they had a genetic predisposition to make the disease survivable.

If so, is that component broad, a contributor to the base immune system, or is it just as narrow as regular immune system which will not protect against a virus/bacteria only slightly different from one it has encountered?

The contributions which gives "hereditary resistance" to disease are genetic in nature and have little or nothing to do with a given person's immune system.

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  • $\begingroup$ Thank you for the answer! The malaria example is a good one, and it helps narrow down what I can accomplish with my scenario. $\endgroup$ – KeizerHarm Oct 13 at 21:49
  • $\begingroup$ The "Garden of Eden" idea stemmed less from natives dying in droves and leaving the land empty (they would later, but not quite so early) and more from the fact that natives on the eastern seaboard would cultivate land and then abandon it once they moved and had been doing so for many generations. $\endgroup$ – gormadoc Oct 13 at 21:53
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To summarise the findings of all the answers, as I understand them:

  • People of a local population may or may not be more resistant to a disease that's been with them for a number of centuries (the answers disagree).
  • Any such endemic resistance would be in the form of genetic traits - like Sickle cell anemia in African people that happens to make them more resistant to Malaria - not in the form of a general immune system booster.
  • Antibodies to one disease may in some cases give immunity to different, related diseases, but that mechanism cannot be relied upon.
  • A local population is more often resistant to a disease that's endemic to them because a fraction of the population will have had it and be immune to it, thereby preventing that they all get it at once and lose people because they cannot spare the manpower to treat them.
  • For dealing with a foreign disease, the more important factor is that a Native American population familiar with plagues would be culturally better equipped to deal with the new Old World diseases they would still suffer from; for example, they would know to burn bodies and prevent contact with the ill.

Feel free to edit if I have once again misunderstood everything.

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I'm posting this as an answer instead of a comment due to its length, but I want to emphasize the point @user3757614 made above: a major factor in the die-off of Native Americans exposed to European diseases wasn't the disease itself, but lack of care for the sick.

There is evidence for this. A similar situation occurred in the late 19th century: isolated communities of indigenous people were exposed to foreign diseases which in many instances effectively wiped out the populations. However, where there was someone to tend to the sick -- often white missionaries -- to tend to their fires, provide food & water, empty their chamber pots -- the local communities suffered much fewer deaths. (I don't remember the study that documented this, but a skilled researcher ought to be able to find the paper the published this finding.)

Many times having European cultural practices forced on natives peoples was what killed them, not the diseases. One example of this was the Yaghan of Tierra del Fuego, who were accustomed to wearing few clothes that could be kept dry by the small, carefully controlled fires they had in their canoes. When Western missionaries convinced them to wear "more appropriate" clothing made of thicker material, these could not be kept dry by their fires, which led to the natives dying of pneumonia. (The effects of the Tierra del Fuego Gold Rush in the late 19th century also didn't help them.)

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