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In a medieval high fantasy world where magic exists, if there is a geographic area in which living creatures mature and then stop ageing; what would the negative effects of this be; firstly on a small scale, and secondly if it affected the whole world?

Here are the rules:

  • There is a spherical area that is causing creatures who enter it to stop ageing once they've reached maturity. They can theoretically live forever.
  • The creatures are not invulnerable; they can be killed, and they still need to eat and sleep. They simply mature and then don't age.
  • We don't know exactly what is causing this phenomenon, just that it's happening.
  • Any creature that spends enough time (say, a few days) in the area gains the effects, and retains them until they leave; they then go back to normal after a few days.
  • The area is currently localised to a few hundred acres of a forest, but is spreading at a rate of several metres per day, and can cross bodies of water (affecting things in the water) and go through physical objects etc.

The negatives I've thought of so far are:

  • Plant and animal populations going out of control and overpopulating the area.

  • Animals becoming brain dead due to reaching their mental capacity, but their bodies are forced to live on; they just lie around undecomposed.

  • From Alexander's answer: Due to the same individuals continuously reproducing, the gene pool will slowly become stagnant and inflexible, meaning creatures will be less resilient to new strains of diseases or changes in the environment etc.

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closed as too broad by kingledion, elemtilas, Cyn, GerardFalla, Don Qualm Apr 15 at 21:04

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Are they also invulnerable, or just immune to aging? $\endgroup$ – Punintended Apr 15 at 18:40
  • $\begingroup$ @Punintended They aren't invulnerable; they reach maturity and then don't age. $\endgroup$ – user63244 Apr 15 at 18:43
  • $\begingroup$ So, the place is responsible for the immortality? What happens if an animal just leaves the area? And then, what do you mean by "spread" (the magic area is becoming bigger, granting immortality to the surroundings?) ? $\endgroup$ – Argemione Apr 15 at 18:50
  • $\begingroup$ @Argemione currently I'm thinking that it's restricted to the area; when an animal leaves, it starts to age again until it re-enters the area. To make it a bit more threatening, I think the area should be slowly expanding. $\endgroup$ – user63244 Apr 15 at 18:52
  • $\begingroup$ Thank you. What if an animal is harmed? Does it heal, or do you assume that its body has completely stopped evolving? I think you should describe the phenomenon itself a bit more precisely. $\endgroup$ – Argemione Apr 15 at 19:03
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Biological immortality would not lead to overpopulation, because mechanisms that keep the population in check, like the amount of available food and predators are not going away. But immortality (or just a very long lifespan) would be very bad for the survival of a species in the long run.

Normally, nature is constantly experimenting with different genetic makeups, and organisms with different traits are present in a population. If somehow immortality is achieved, genetic variability becomes effectively frozen. This may be good for organisms that carry this specific genetic makeup, but it is very bad, if the environment keeps changing or gets changes suddenly. A simple disease will wipe out the entire species, because there will not be enough young individuals that carry a variant which could make them resistant to this disease. Consequently, from evolution standpoint, a species' lifespan has an optimal length. Too short would affect reproduction and proliferation of "good" genes, and too long would make the species genetically inflexible and vulnerable to any change in the environment.

Going "brain dead" is not a valid concern, imho. It is not like our brains are running through a fresh supply of unused neuron cells and shut down once this supply is exhausted. We are rather reusing existing cells for our entire adulthood. However, cognitive capacity would indeed be diminished in immortal species, but not to the point that they would be physically unable to learn any new things.

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