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In a world I am working on, I have a wilderness-living, social, group-living species that for various reasons lacks access and ability to anything resembling modern medicine, including vaccinations. Yet, I want to keep it such that absent physical injuries, adults of this species very rarely become visibly sick or infirm, even when affected by what would ordinarily be relatively serious illness. The world they exist in is very much Earth-like, and might very well be Earth, but is not guaranteed to be Earth specifically.

These creatures are biological beings that evolved according to the theory of evolution as currently scientifically understood, with no superpowers, magic or "intelligent design" involved (except to the extent that I have an idea in mind and am working backwards to figure out how they might have evolved that way and if that is possible). I haven't yet decided on the exact form for this, but they have largely human-level intelligence.

How can I arrange their environment such that adults generally do not become sick, and when they do, that the effect on the individual is generally limited such that they basically remain able to function at a level similar to that of healthy individuals while their bodies are fighting off the disease?

It's perfectly acceptable and perhaps even good if some medical conditions cause a significant reduction in ability to function in some individuals (particularly very young and very old), but I want adults to for the most part be able to simply shrug off most illness.

Please don't just say "evolutionary pressure"; that's a given. Rather, be specific as to what could give the effect described. Bonus points for references and real-world examples, but any well-reasoned answer that would not break suspension of disbelief is welcome.

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    $\begingroup$ Just a note, as there have been a few comments here on this: Users do not have to accept answers to their questions. Please do not pester them to do so. $\endgroup$ – HDE 226868 Feb 21 '17 at 18:13
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Although you can modify the environment, the best way to change things is often to change yourself. My point : change this species' immune system.

We humans have various difficulties facing diseases, due to our constitution, but certain plants do not have these difficulties. Here is a Wikipedia article about plants resistance to diseases.


Now, immune system isn't everything, you also have to eat well, be happy, go out often, and a few other things, as stated in this wiki how article Note that most of the pieces of advice in this article are easy to implement in your story, due to them living 'into the wild'.

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  • $\begingroup$ The problem with this is that many "illness symptoms" are not symptoms of the disease at all, but rather of the body's immune response, fever being the best-known. This is why chicken soup is such a well-known folk remedy: there are naturally-occurring immunosuppressants present in chicken meat. (It actually makes your illness worse, by making the immune process drag on longer and giving the disease more time to rampage around your body, but at least you don't feel quite so bad while it's happening!) $\endgroup$ – Mason Wheeler May 5 '16 at 20:50
  • $\begingroup$ You're right. That's why I added the 'go out often' part. As long as you're healthy, you're able to endure the symptoms rather well. $\endgroup$ – Nathan Coustenoble May 5 '16 at 20:54
  • $\begingroup$ @Mason Do you have a citation for that? (If so, you might also want to add it to skeptics.stackexchange.com/questions/14721/…) $\endgroup$ – mattdm May 5 '16 at 23:21
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The antidote for any poison is always nearby

...the cure for any disease is also nearby.

It is a trope in some books (Discworld I think is one) where the poison and it's antidote are often found very near to each other. If one were to order a world in a similar manner, then even if an individual got sick they wouldn't endure any severe symptoms after taking the nearby cure.

Evolution

If this world has a higher than Earth mutation rate in microbes/viruses/fungi then the immune systems of the creatures in that world will be optimized to identify and counter immunological threats very quickly and neutralize them. When everything that hits an immune system is new and lethal, the immune systems over time will get very good at countering those threats quickly.

Evolution Combined!

Simply asserting in your story that a complex web of chemical and biological warfare existing in your world is plausible since modern science on earth is just now starting to get a handle on the biological interactions in stuff as simple as cheese. There are definitely complicated interactions between various plants and animals here on earth.

It is not unreasonable to assert that on this planet or in this ecosystem, it is beneficial for the poison and it's antidote to be close by. To use an earth analog, the antidote for botulinum toxin might be found by eating the mushrooms that grow on pig carcasses.

So, these creatures that can't get sick: they possess inspiringly powerful immune systems but in those times where the immune system is compromised, the antidote or cure is found in a nearby plant, animal or mushroom.

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  • $\begingroup$ IMO these two suggestions are different enough that they probably warrant(ed) being posted as separate answers... $\endgroup$ – a CVn May 5 '16 at 14:40
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A "wilderness-living, social, group-living" organism would (I assume) be in herds that move at the rate of their slowest member. If the slowest member is sick, then the herd will slow and that could be bad (predators, food source, climate, etc).

One stable strategy would be for the herd to turn on anyone sick and kill them.

Another stable strategy would be for the herd to help the sick in an altruistic, "selfish gene" way. How that is achieved practically is up to you - sharing antibodies via milk, slime or other bodily fluids; mobile immune system elements (something flea-like perhaps?); maybe the immune system is under conscious control so they can discuss and control how best to react.

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To create an environment that minimizes disease within a “primitive” society, you need to discourage situations where pathogens can easily multiple or spread. The following factors can help:

  1. Basic hygiene (i.e. bathe occasionally)
  2. Basic sanitation (i.e. don’t mix drinking water and waste)
  3. Few, if any, domestic animals
  4. Significant geographical distance from species’ point of origin
  5. The climate is cold or otherwise inhospitable to the majority of pathogens
  6. Contact between distant populations is rare (i.e. no Silk Road)

How do these help?

  • 1 and 2 should be obvious; both are well known to prevent the spread of disease and eliminate conditions that allow pathogens to thrive.
  • 3 and 4 will vastly reduce the opportunities for pathogens to spread to your sentient species from another species; there would be no hosts with a similar physiology
  • As for 5, pathogens will have a harder time surviving as a species if they can’t live outside a host for long
  • 6 is important for maintaining immunity; when distant populations interact on a somewhat regular yet infrequent basis (i.e. annually) it provides plenty of opportunities for pathogens; it will mutate within one population then spread to the other population that has not had an opportunity to develop immunity to the new variant.

For an example of how these factors make a difference, compare the Americas and Europe in the Pre-Columbian era. All of the above factors were prevalent in the Americas, but far less common in Europe. (Regarding #5, it’s theorized that traveling through present-day Siberia and Canada killed off a lot of the diseases the first migrants would have brought to the Americas.) This disparity was a major factor in events such as The Great Dying, a massive plague that’s estimated to have killed as much as 95% of Native Americans in New England as well as many more throughout the Americas[1][2].

So, in short, a “primitive” society will naturally have few diseases without any special adaptations or accommodations beyond some basic hygiene.

1: http://abbemuseum.org/research/wabanaki/timeline/great-dying.html

2: http://www.pbs.org/gunsgermssteel/variables/smallpox.html

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Provide the creatures with natural analogs of vaccines and/or antibiotics.

You could allow for more expansive capabilities to exchange antibodies from one individual to another. In mammals, this occurs but is limited to lactation. Invent a mechanism where once an individual survives a serious illness, they can transfer resistance to the rest of their group. This would seriously curtail endemic diseases.

For antibiotics, an idea could be to allow for symbiotic/mutualistic relationship with another species (of mold?). The individuals might maintain a baseline of the symbiont, and then "activate" it when under stress from disease (only activate when needed to avoid creating antibiotic resistant strains). A symbiont augmented immune system might plausibly provide "super" capabilities.

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Most bacteria or virus-related diseases are flushed from the body in a manner of weeks, once the host's immune system has had time to mobilize and respond to that particular threat. The disease then only survives by constantly migrating from host to host (and perhaps mutating fast enough that after some hundred or so transmissions, previously infected hosts can be re-infected.)

Its conceivable that if everyone was just alone for long enough, all of these kinds of diseases would be absolutely wiped out, since they were unable to find new hosts before being defeated in their current hosts. (I want to link to the relevant XKCD What If, but I think this was only in the book.) A lifestyle where these individuals spent most of their time on their own would thereby likely lead to absence of communicable diseases.

Less drastic measures to do the same thing might simply involve making disease transmission less likely for these creatures- perhaps their upper respiratory tract is designed in such a way that they can't cough or wipe their nose on their hands. Remember that for a disease to continue to exist, the average infected host must infect at least one other person; otherwise, it soon dies out.

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  • $\begingroup$ "A lifestyle where these individuals spent most of their time on their own" seems to go rather counter to the fact that the species is a "social, group-living" one as stated in the question. $\endgroup$ – a CVn May 5 '16 at 16:08
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Infectious diseases don't particularly want to kill their hosts, they just want to spread more and don't mind harming the host in the process. The most damaging diseases are recent introductions to the host from another species (e.g. HIV or Ebola in humans).

If you can arrange a long-term stable evolutionary environment with little inter-species interaction, then maybe diseases have just adapted so well to their hosts that they don't make them that sick but still spread.

That still leaves non-infections things like cancer or auto-immune conditions, but maybe this species is just resistant to those too - like some on Earth are e.g. naked mole rats never get cancer.

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At some point in the (evolutionary) recent past, all animals related to this species were wiped out. (Think no other mammals aside from humans still existing.) It is difficult (though not impossible) for viruses to go cross-species, and the genetic distance won't help. Any viruses that would affect them died out shortly thereafter when they ran out of non-immune hosts, because there is little cross-group movement.

This still leaves bacteria and a few odds-n-ends, but could be a useful component.

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