Inspired by the “Earth’s holding capacity” thread, what is the smallest number of people needed to keep things going the way they are?
If a plague evenly decimated humans across the planet, what would be the smallest number needed to ensure that “civilisation” (that is, the state of the world as we know it, generally) didn’t collapse?
Things seemed to be going ok at the beginning of the 20th century, and there were (I’m guessing) maybe a billion people around then?
Well the population of Australia was around 7 million in the late forties/early fifties. At that stage Australia was completely self-sufficient. Manufacturing of cars, airplanes, electrical goods and virtually everything else was carried out here using Australian mined and refined materials. All medicines AFAIK were manufactured here, or at least could be manufactured here. There was a good self-sustaining education system with numerous universities and technical colleges to provide training to future generations. Australia was a massive exporter of agricultural goods and ore at the time so obviously their was an oversupply of materials and the standard of living was ridiculously high. Based on this we can reasonably surmise that if you define civilisation as being 1950 level then 7 million is more than enough. I suspect the question would depend on the level of infrastructure and population concentration already available when you started and where you’re setting up camp. If you insist on saying that after the plague the USAF couldn’t gather up all survivors and move them Miami or Sydney then the number would have to be much higher. If we can concentrate the survivors on one continent with a large raw material resource base then I’d say that 5 million would probably be able to sutain a civilisation.
Decimated means we lose ten per cent, technically. But I know the modern usage means “largely destroyed” so I won’t quibble.
Oh yeah, and your guess regarding the population at the turn of the century seems flawed. In 1900 I suspect we could quite easily have removed the population of the Indian subcontinent and Indo-China, Australia, all of SE Asia, most of Africa, large chunks of south America, huge chunks of Russia and Eastern Europe and most of China and Japan and had no appreciable effect on ‘civilisation’. I mean here civilisation in the sense of technology and modern industry. Those areas simply had no industrial base really worth considering, or that wasn’t duplicated elsewhere in the world. In reality ‘civilisation’ at this stage was concentrated in Western Europe and North America. I see no reason why those two alone couldn’t have been fully self-sustaining.
New Zealand is a first-world nation and geographically one of the more isolated places on the planet. It has heavy industry, and relies heavily on hydroelectric and other non-fossil power sources, and has a literacy rate of 99%, so I think you could argue that it is self-sustaining, or could be if necessary. Population is approximately 3.8 million.
However, NZ is also concentrated, geographically and population-wise. I think one could take Gaspode’s observations and my own and guess that the number of survivors would have to be high enough to ensure a quick re-concentration in the several millions. The total number of survivors might have to be much, much higher. There’s a lot of folks in Montana who wouldn’t come out for anything.
If you selected your survivors, the number required to sustain civilization might not need to be nearly as large. We don’t have to postulate mass-death to consider it, either. Instead, it could be considered it in terms of, say, an extrasolar colonization attempt, with no hope of regular contact or resupply from Earth.
Tedster said that “decimated” means a loss of 10%. The 1500 original population was “decimated” to the tune of 90% by European diseases. In South and Centeral America, the descendants of that 1500’s population maintains a solid degree of “civilization” (albeit, 400 or so years after their decimation).
Gaspode: No complaints, but not to forget that the City-state of Athens (circa 300BC or so) got much of their resources via a system of “colonies”. Maybe the constraint of “resource self sufficiency” isn’t as quite as vital as you imply with your example of Australia (or as Sofa did with N.Z.) 
The amount needed to sustain civilization, it would seem to me, would be proportional to the amount of survivors. If there are 3 billion survivors obviously you’ll need about 2.5 billion (WAG) working to keep things running. If however, you had like 20,000 survivors you’d need substantially less than 2.5 billion. Maybe about 15,000 (again, a WAG.)
If we define civilisation as somewhere fairly organised with laws then all that would really be required is that some kind of ‘order’ would remain.
The greeks / romans had few numbers compared with today but had ‘civilisation’.
Several aspects of what we, today, call “civilization” have been forgotten, I think.
We’ve got computers. We will almost certainly want to insure that we can support computers and advances in computer technology. This might call for even MILLIONS.
Do we want to try to defend against an asteroid. If so, several more millions will be needed, devoted to just this one task.
Do we want to continue with deep-water oceanographic research. At least another million for that infrastructure.
Advancing and producing consumer electronics? Another couple of millions.
There’s MUCH more to think about in 2001 than there was in 1940. We COULD, of course, just “drop back” but why stop at 1940? Skip back to horses for transportation and things get a LOT easier. “Early to bed and not-too-early to rise” and we can skip back to wood-burning stoves and no lighting.
BUT: Do we want to do that? I don’t.
I not only want “society” to keep what we’ve got now but would like to be able to continue to advance in knowledge and (technological) abilities.
Sea Sorbust: When a deadly virus is killins literally billions, I don’t think that deep sea research or consumer electronics will be immediatly necessary. Mabye once things leveled off those things would be nice, but they’re certainly not necessary.
Qwertyasdfg, you assume that a “deadly virus” is the way we might go from a vast population to a smallish one. Maybe the most likely biochemical mechanism is from genetic tinkering—to the extent that most-all of us will be unable to inter-breed: No babies.
Under such circumstances, we will probably have the means to do artificial reproduction but why would we try to go back to, and maintain, a population of billions again? Better to pick some “sustainable” number (and some “sustainable” locales) and try to get back a numerically constrained, but naturally breeding, population of humans.
Another unpleasant scenario might be a large asteroid strike. There might well be some unaffected places where the damage is little more than a mild-to-medium earthquake. As the population rebuilds from, say, 50,000 to something, why not find an “optimal”, sustainable population size and avoid all the problems that we’ve had during the past dozen or so decades due to OVERpopulation?