I have an epidemic of unknown origin spreading across the earth. The effects are decrease in cognitive ability to around 80+ IQ. So we have a surgeons who don't know how to operate, engineers who don't know math, composers who can't read notes, programmers who can't code, writers who could barely read, judges who don't know the law etc.

On average it takes several years for a complete transformation, with large variance between individuals. At first the effect is very slow, but the ability loss accelerates near the end. Since there is no way to test for the epidemic, beside loss of ability everybody is on a edge. Slight fell of performance and people start to believe that you are infected. Since there is no cure, you could easily lose your job and your college degree becomes useless.

What's minimal percentage of a normal population should I keep in order to keep the civilization running?

I want services like water, sewage, electricity, transportation still running. I want minimum of people who could fix our machines. My aim is to present civilization under severe stress but still barely functioning. Something like a third world country with huge brain drain problem

My aim is something like 10-20% immune, with cutting the rich country services, and retraining remaining humanities, surplus lawyers, bankers, high frequency traders, marketers, non-profit activists, humanities etc.

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    Welcome to worldbuilding. To familiarize yourself with this community it's advised to take the tour and visit the help center. – L.Dutch Dec 7 at 19:31
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    @Renan compared with present – Desai Dec 7 at 20:42
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    IQ is not a biological measure, it is largely a test of how close your upbringing is to a middle class white male from an industrialized country. – John Dec 7 at 20:55
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    @John - Can you back that up with references to meaningful research? I believe that non-white Asians have a mean IQ greater than that of white people, even though the test wasn't designed for their benefit. – chasly from UK Dec 7 at 20:59
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up vote 4 down vote accepted

IQ is not as simple as you may think. There are many different types of intelligence, including logistic, spatial, musical, interpersonal, intrapersonal, and naturalist, to name a few. Most IQ tests, which are used to produce the famed "IQ Level", only tackle logistic and spatial intelligence, without crediting a person's other mental abilities.

So, essentially, what your virus does is simply limit a person's ability to perform calculations, form hypotheses, and visualize the world around them. While this will affect everyone significantly, most jobs do not rely on those skills whatsoever, with interpersonal, linguistic, naturalist, and bodily-kinesthetic being far more important intelligences to have in most people's careers. Only highly technical positions, such as scientists and engineers, will be impacted heavily by this virus. Heck, the virus won't even remove a person's ability to read, which is the most valued skill in any job hands down.

So while your virus may inhibit research, invention, and technological progress in general, a majority of the population will continue to move on as usual, without losing their livelihoods or anything drastic like that.

  • McNamara shared your belief. He even tried his luck in conscripting low IQ individuals in to army with slightly more training. Let's say it turned out that in army actually thinking even among low ranks was necessary. – Shadow1024 Dec 8 at 13:47

Although it varies widely depending on the profession we are talking about and the country, and you also have people with abilities unemployed, things are barely working as they are. You don't have enough professionals for everyone in the world as it is. I'd guess you need 85/90 of people immune. On the other hand, knowing of the problem, efforts would be made to qualify enough people to replace the ones that retire over time. Professionals would have to work overtime as teachers and they would be supervised in case they are infected, but they could maintain the balance. With that system in place you could lower the critical percentage a a bit.

  • Whilst I see what you're getting at, what a contemporary economy considers 'enough' is never met, it can never be because of economic principles that are established and maintained as a result of existing conditions(assumptions of finite supply, expectations of relative wealth etc.) Agriculture and essential services utilize a fraction of the total number of people they once did to provide for multiples of the total people they once did... yet 'we don't have enough people or we don't have enough jobs' etc. Minimum limits of functionality are a part of the question. – Giu Piete Dec 7 at 21:17

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