May be the wrong site, but researching for a writing project... What effect would there be on a group of humans living in a lightless and cramped environment (assume underground) for nearly 800 years, assuming that some form of nourishment is available?

  • $\begingroup$ Also, as an out of the box solution, can I burn some of that nourishment to make light? 800 years is a long time. Someone's bound to get creative eventually! $\endgroup$
    – Cort Ammon
    Mar 16, 2018 at 21:49
  • $\begingroup$ I am writing a story with the same premise. Also, play some Fallout for ideas. $\endgroup$ Mar 16, 2018 at 21:50
  • $\begingroup$ The effects im aking about are the overall effect... And trying to get information from individuals with an actual scientific grounding in fields relating to mental and physical "being"... It's research for a story im working on. I'm trying for as accurate as possible to allow for a reasonable level of "what if?" $\endgroup$
    – wolf
    Mar 16, 2018 at 22:06
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    $\begingroup$ Lightless as in completely dark? How cramped is cramped (underground doesn't have to mean "cramped")? $\endgroup$
    – RonJohn
    Mar 16, 2018 at 22:29
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    $\begingroup$ Related (about individuals, not humanity over hundreds of years). $\endgroup$ Mar 16, 2018 at 22:40

3 Answers 3


It is unlikely. You have multiple problems to solve quite apart from the inbreeding.

Total lack of light would probably kill them all pretty quickly as they go insane. Insanity would be a major problem pretty quickly, and how would you deal with people who start lashing out in the dark? Discipline would break down into chaos.

Airflow, we can't breathe the same air for 800 years in cramped conditions, there needs to be a source of fresh air.

Food, we cannot live on a single food source, we need a plethora of elements in our diets to remain healthy.

Vitamin D we mostly get from sunlight, without it we need an alternative source.

Many more factors I would think, but the humans themselves would be the worst problem. You can't keep any sort of discipline in this situation and people will go crazy.

  • $\begingroup$ Great, so many things we cannot do without light from hygiene, medical work to food distribution that it would all fall apart in weeks probably.if not days. Sensory deprivation has been used as torture, and it will drive people insane over quite brief periods of time. $\endgroup$
    – Kilisi
    Mar 17, 2018 at 4:02
  • $\begingroup$ The premise that i was hoping science would match (to a point), was that it would be possible, albeit with large scale inbreeding after the first generation alongside cannibalism and insanity, with physical deficiencies. And maybe by the third generation a tiny group of aware individuals with an inkling of the problem. At least now i know i will need to explain away a few problems. Again, thank you $\endgroup$
    – wolf
    Mar 17, 2018 at 4:10
  • $\begingroup$ Glad I helped, but this would never get past the first generation, and cannabilism of raw human meat involves even more problems, cooking people without a light producing heat source would involve a hot spring or something and even more problems...You may have a tiny number of survivors I guess, but they would be totally insane and unlikely to breed sucessfully. $\endgroup$
    – Kilisi
    Mar 17, 2018 at 4:16
  • $\begingroup$ More research... Ugh. Well i learned some things at least. $\endgroup$
    – wolf
    Mar 17, 2018 at 4:17
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    $\begingroup$ Torches and lamps? Fire using wood from wagons (possibly part of the"exile")? $\endgroup$
    – wolf
    Mar 17, 2018 at 4:35

Depending on what nourishment exactly is available your humans may suffer from Vitamin D deficiency.

You can get some from food, but mostly quite specific animal products (oily fish, red meat, liver and egg yolks, all of which might be hard to come across in a cave) and the vast majority is created by sunlight on your skin.

The main side effect of a Vitamin D deficiency is soft bones, rickets or osteomalacia. This has a whole host of side effects, the main one being bones break very easily (and in a lightless cramped cave that's probably not a good thing) but also some physical deformities like bowed legs and curvature of the spine, thicker wrists, ankles and knees, and 'pigeon chest’, where the breastbone sticks out.

Combined with inbreeding you might find your population quickly becomes a race of hunchbacks.

  • $\begingroup$ Would there be any alternatives to vitamin d that could reduce the odds of rickets? $\endgroup$
    – wolf
    Mar 17, 2018 at 1:18
  • $\begingroup$ Eggs, fatty fish like salmon, mackerel and tuna, orange juice and some grains provide vitamin D. $\endgroup$
    – Dan Clarke
    Mar 17, 2018 at 2:57
  • $\begingroup$ @wolf not as far as I'm aware. It's a pretty essential vitamin unfortunately $\endgroup$ Mar 17, 2018 at 9:46
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    $\begingroup$ Vitamin D is only produced as a result of cholesterol (or its fungal analogue) being exposed to ultraviolet light. If your humans don't receive sunlight, they must regularly eat something (or eat something that ate something) that was exposed to sunlight. $\endgroup$ Mar 17, 2018 at 15:47

You do not say how large your group is. The main problem with an isolated group over 800 years is inbreeding.


italics mine

The isolation of a small population for a period of time can lead to inbreeding within that population, resulting in increased genetic relatedness between breeding individuals.

Many individuals in the first generation of inbreeding will never live to reproduce. Over time, with isolation, such as a population bottleneck caused by purposeful (assortative) breeding or natural environmental factors, the deleterious inherited traits are culled.

Island species are often very inbred, as their isolation from the larger group on a mainland allows natural selection to work on their population. This type of isolation may result in the formation of race or even speciation, as the inbreeding first removes many deleterious genes, and permits the expression of genes that allow a population to adapt to an ecosystem. As the adaptation becomes more pronounced, the new species or race radiates from its entrance into the new space, or dies out if it cannot adapt and, most importantly, reproduce.

The reduced genetic diversity, for example due to a bottleneck will unavoidably increase inbreeding for the entire population. This may mean that a species may not be able to adapt to changes in environmental conditions. Each individual will have similar immune systems, as immune systems are genetically based. When a species becomes endangered, the population may fall below a minimum whereby the forced interbreeding between the remaining animals will result in extinction.

So too your group. The population will decline after a couple of generations because of inbreeding depression. They might die out. If they don't die out but instead weed out deleterious alleles, there will likely be a pronounced founder effect from the survivors, and these people after 300 years might be fairly different from the starting population.

Some recessive genes which persist into this population might not be so disadvantageous to them; blindness, obviously, but also mutations which produce slowness, lower metabolic rate etc. There may be mutations which are irrelevant to the lightless circumstances but which arise because of chance and the founder effect - for example, they all have unusually shaped ears. If their environment exerts any sort of selective pressure on them (you decide) such that certain characteristics improve the likelihood of leaving children, you could have selection for those characteristics.

800 years is not very long for humans, evolutionarily. But evolution can happen fast in isolated groups.

  • $\begingroup$ Thank you, i recognized the inbreeding but didn't realize that it could be an issue with populations that size (my initial population was planned to be 2000 or so fanatically devout Catholics, with the ingrained sexual taboos). Could selective breeding be feasible in a population that size? $\endgroup$
    – wolf
    Mar 16, 2018 at 22:15
  • $\begingroup$ More on that here: worldbuilding.stackexchange.com/questions/3/… $\endgroup$
    – Willk
    Mar 16, 2018 at 22:53

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