Whoever travels to the americas, - will disease always wipe the native peoples?

I would add a fifth one: genetic exchange between Native Americans and settlers, which would very rapidly introduce heterozygosity into the population. Even if it's just for one generation, the added diversity could mean the difference between complete extinction and severe devastation of a community.
So, that one theory about the Roanoke settlers turned up to the maximum?
 
Smallpox tended to run in cycles. There would be an outbreak, a fair number of sick and about 30% die in the European population. Then you have a large number of immunes so you have isolated cases but not a raft of susceptibles. After a time as you get a large population that has not been exposed you have a condition for an epidemic again. To get more genetic diversity in the Americas you need a lot of baby making contact, over lots of generations, and over a significant distance. Yes there were significant long distance trade routes amongst natives in North America, Central America, and South America but the actual genetic exchange was much less than the exchange of goods. You'll get a cluster of genetic diversity around where the "foreigners" are, but this will spread very slowly - there are excellent studies on movement of genetic diversity in populations with limited transport (ie foot, canoe, etc). A child of the first generation who has 50/50 native/foreign DNA will be at least 15 before it is likely they would be spreading DNA at any distance from home. Also note that any children of this child will have approximately 75% native, 25% foreign DNA. Foreign DNA will get diluted out pretty quickly unless reinforced in some way, although bits and pieces will survive.

OTL a great deal of the spread of disease among Native Americans was due to the aforementioned trade routes. One well documented example is the spread of smallpox and other diseases from the Upper Hudson area (Albany) where the Dutch had a trading center for furs. Using rivers and the Great Lakes, the natives travelled large distance for this trade, going home they brought disease to places no white would see for decades.
 
Also note that any children of this child will have approximately 75% native, 25% foreign DNA. Foreign DNA will get diluted out pretty quickly unless reinforced in some way, although bits and pieces will survive.
In terms of the total genome, yes, the foreign DNA will get diluted rapidly, but we're not really concerned with the total genome. With regards to the genes involved in the MHC, IIRC there is limited recombination of those genes during meiosis, meaning that "Old World" MHC genes don't really get diluted by half each generation. And since MHC genes are codominant, a child of 50/50 native/foreign parentage will potentially have more MCH diversity than either parent, and half of their kids will get largely Old World MHCs and half of their grandkids and so on.

It's important to keep in mind though, that MHCs don't confer resistance to a particular disease but rather diversity in MHCs makes it more difficult for pathogens to overcome the immune system and infect all members of a population.
 
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It's important to keep in mind though, that MHCs don't confer resistance to a particular disease but rather diversity in MHCs makes it more difficult for pathogens to overcome the immune system and infect all members of a population.
Thanks for this. So many people seem to have the idea that an Old World genetic inheritance automatically confers immunity to every disease in history. The role of recurring endemic "childhood diseases" in creating many of the "standard" antibodies is completely overlooked.

There is also that thing I never know how to describe in proper immunological terms, whereby the immune system is "turned" sometime in infancy to either work most effectively against macroparasites--worms, slugs, parasites of that nature, versus microparasites. A community lacking significant microparasites will leave the system to optimize against the former, leaving them that much weaker against the sudden appearance of the latter.
 
Like a lot of the human ecology, the immune system learns better in youth, not so well in older age. The mania for using sanitizer in everything near young children 24/7 has been shown to be deleterious as since the immune system is not challenged by rather common "invaders" and therefore is less efficient in dealing with them later on. The whole immune system issue is quite complex, and multifaceted. As far as the histocompatability complexes are concerned, they are not excluded from Mendelian genetics - to the extent any particular expression is dominant it will be more persistent those that are recessive less likely to be persistent. To use a crude but apt analogy, if you have big basin of water and you want to change it from clear to a color, you'll need a fair bit of dye. Additionally, as I stated before, even if you have a lot of local/foreign reproduction, that does nothing to help the pre-existing population for resistance in that area, and as you go further away, diseases will travel muhc much faster than the spread of positive genetic material.
 

raharris1973

Gone Fishin'
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North America in 1600 for instance was a mess versus 1500; the English colonists often found whole towns abandoned due to plagues having decimated the peoples living there just handfuls of years before they showed up--traders out of the Spanish and other southerly colonies tended to plant the seeds of destruction on the coasts.

This is what makes me wonder if native genetics and preservation of parts of native culture in North America might have been greater if the DeSoto expedition actually turned into a conquest, followed by setting up a Spanish ruled Kingdom, Spanish settlers, etc than the "hit and run" job it was in OTL.

In other words, although it is in many ways a miserable racial caste system with exploitation, maybe Europeans sticking around and organizing the local hierarchy, any hierarchy, is better for preserving more of the genetic lines and for documenting culture than for the Europeans to pass through, spread devastation and disease, then leave and have hierarchy and specialization totally collapse.

Just trying to figure out here why the Aztecs and Inca and Maya and Guarani and Tupi are fairly central to the identity of modern Mexico, Peru, Guatemala, Paraguay and Brazil, but the Mississippians are an obscure footnote to US history.

The other advantage of a Vinland contact is diseases won't hit in repeated tsunamis, multiple hits in a single generation. The major contact point will be Iceland, which was simply too small to support epidemic diseases. So smallpox, for instance, did hit, but was often a couple of centuries between epidemics.

With Old World entry into the new world limited by a bottleneck in Iceland for several centuries, I could see the Amerindian Norse be very, very susceptible to diseases from later waves of migrants.

This could result in their Vinland societies being overrun by conquerors from more "crowded Europe".

Also, maybe Vinland could try to develop some quarantine practices (not that these would work), like the idea of buying Africans from Portuguese might be a neat way to get more grain planted and churches built, but diseases come soon after, so Vinlandic communities boycott the slave trade for that reason.
 

ar-pharazon

Banned
The main problem was lack of immunity and genetic diversity.

One tribe loses 90% of its population and flees joining another tribe and spreading the disease thus causing a chain reaction that killed millions.

Disease is what gave the Europeans the America-not their guns, or horses or steel or the Amerindians own politics and struggles.

So I looked, and behold, a pale horse. And the name of him who sat on it was Death, and Hades followed with him.”

Smallpox and it's affect on the Amerindians was so destructive I think this biblical passage is appropriate. Because disease was the terrible sharp sword that left the Americas wide open for European conquest and settlement.
 
Thanks for this. So many people seem to have the idea that an Old World genetic inheritance automatically confers immunity to every disease in history. The role of recurring endemic "childhood diseases" in creating many of the "standard" antibodies is completely overlooked.

There is also that thing I never know how to describe in proper immunological terms, whereby the immune system is "turned" sometime in infancy to either work most effectively against macroparasites--worms, slugs, parasites of that nature, versus microparasites. A community lacking significant microparasites will leave the system to optimize against the former, leaving them that much weaker against the sudden appearance of the latter.

Yes but we have a Eurasian population which was isolated enough that they wasn't able to upkeep immunity, meaning when a disease hit them, it was virgin territory every time. That population was the Icelanders, and the result was that they lost 1/3 of their population when a epidemy hit. Yes that was bad, but it usual only took 60 years to reach the old population agaion, and that was with massive infant and birth fatality (in some areas 70% of all newborns died).
 
Given how they were affected by European pathogens perhaps the only group of possible contactors that would not cause a devestating series of illnesses would be the Polynesians.
 

raharris1973

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How far back in Eurasian history would one have to go to find large swaths of land (besides the Iceland example above) that were of similarly limited genetic diversity to the Amerindians?

Strikes me that it may need to be paleolithic.

Cortez lands in Bronze Age Spain - disease probably still doesn't hit the downtime Iberians anything like it hit the Amerindians.
 

Marc

Donor
A coda to this thread:

An unavoidable plague holocaust, followed by a predictable, land clearing, semi-genocide, finished off with a certain ruthless subjection.

The miracle is, is that there are any Native Americans left. And that they managed to save or salvage, some meaningful fraction of who they are...
 
As far as the histocompatability complexes are concerned, they are not excluded from Mendelian genetics - to the extent any particular expression is dominant it will be more persistent those that are recessive less likely to be persistent. To use a crude but apt analogy, if you have big basin of water and you want to change it from clear to a color, you'll need a fair bit of dye.
Thats not how dominant/recessive alleles work...Without active selection, all alleles are equally persistent.
If you were selecting against a trait, say brown eyes for example, dominant alleles would be easiest to remove and less persistent. In an obligate outcrossing species like us (i.e. we can't fertilize our own eggs), recessive alleles are more persistent and pretty much impossible to get rid of completely since anyone heterozygous for the gene has the recessive one "hidden" by the dominant allele. And the rarer the recessive allele becomes, the more difficult it will become to eliminate it entirely.

Anyway, the alleles involved are codominant, not dominant, so the above is irrelevant.
 
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