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托马斯 · 马尔萨斯和种群增长

托马斯·马尔萨斯对于种群的看法。马尔萨斯极限。 Sal Khan 创建




the 1700s in Europe are often referred to as the age of enlightenment it was a time we had come out of the Renaissance we had rediscovered science and reason and in the 1700s we saw that come about with even more progress of society as we exit the 1700s and enter into the 1800s we start having the Industrial Revolution and people saw the steady march of human reason of human progress and because of because of this a lot of people were saying hey humanity could we'll continue to improve and improve forever to a point that poverty will go away we will turn to this perfect utopian civilization without Wars without strife of any kind and there was something to be said about that you had significant improvements in fact you had even more dramatic improvements once the Industrial Revolution started but not everyone in the late 1700s was as optimistic and one of the more famous not so optimistic people was Thomas Malthus Thomas Malthus right over here and I will just quote him directly this is from his essay on the principle of population the power of population is so superior to the power of the earth to produce subsistence for man that premature death must in some shape or other visit the human race very uplifting the vices of mankind are active and able ministers of depopulation they are the precursors and the great army of destruction and often finish the dreadful work of themselves but should they fail in this war of extermination sickly seasons epidemics pestilence and plague advanced and terrible or inter in terrific array and sweep off their thousands and tens of thousands should success still be incomplete gigantic inevitable famine stocks in the rear and with one mighty blow levels of population with the food of the world so not not so uplifting of a little quote right over here but this was his general sense he lived in a time where people were being very optimistic that progress the march of progress would consider would go on forever until we got to some you in civilization but from thomas malthus's point of view he felt that if people could reproduce and increase the population they will that there's no way of stopping them so from his point of view the way he saw it so let me on that axis let's say that that is the population population and this axis right over here let's say that that is time so by his thinking and everything that he'd seen in reality up to that point would would back this up that if people had enough food and time they would reproduce and they would reproduce in numbers that would grow the population so in his mind the population would just keep on increasing it'll just keep on increasing until it can't support itself anymore until the actual productivity of the land can't produce enough calories to feed all of those people so in his mind there would be some natural upper bound based on the actual amount of food that the earth could support so let's say that this is let me do that in a different color so in his mind there was some upper bound there was some upper bound and once you get to that upper bound then all of a sudden the vices of mankind will show up and if those don't start killing people then all of these other things will epidemics pestilence plague and then and then famine people are actually starving to death so in his mind once you got to this level maybe you had a couple of good crops people are feeling good about themselves they overpopulate but then all of a sudden you have a bad crop or because you have a bad crop people start fighting over resources and wars happen or maybe the population is so dense that a plague develops and then you have a massive wave of depopulation and so you would just oscillate around this limit and this limit some people refer to as a Malthusian limit but it's just really the limit at which the the population can sustain itself and from thomas malthus's point of view he did recognize that there were technological improvements especially in things like agriculture and that this and that this line was moving up he had seen it in his own lifes in his own lifetime that this line had moved up but from his point of view however far you move this line up the population will always up and sate forward and catch up to it and eventually get to these Malthusian eventually get to this limit and then the same kind of not so positive things that he talks about would actually happen and some people now say Oh Thomas Malthus he was so pessimistic he was obviously wrong look at what's happened we have so much food on this planet right now we've gone through multiple agricultural revolutions and they are right in the last 200 years since Malthus so since the early 1800s we really have been able to outstrip population so this line this line up here has been moving up much faster than even population so right now we actually do have more calories per person on the planet than we have had we've had at any time in history but it's not saying that Thomas Malthus was wrong it's just saying that he maybe he was just a little bit he was he was a little bit pessimistic and when that that limit will be reached now the other dimension where you might say that he was maybe wrong was in this principle that a population will increase if it can increase if there is food and if there is time people will reproduce and a good counterpoint to that is what we've now observed in modern developed nations and soul is this right over here shows the population growth I got this from the World Bank but the population growth of some modern developed nations and you can see the United States is is pretty low but it's still positive it's still it's still well it's it's still over half a percent and but even that adds up when you compound it but if you look over here Japan and Germany and Japan and Germany have less immigration than the United States if you especially Japan they are actually negative so just this population left to its own devices if you especially if you account for people not going across borders just the population itself growing they actually have negative growth so there's some reason to believe that this is evidence that Thomas Malthus was wrong he didn't or not completely right he didn't put into account that maybe once a society becomes rich enough and educated enough that they might not just populate the world or have as many kids as they want they might try to do other things with their time what whatever that might be so I just wanted to expose due to this idea time will tell if thomas malthus if we can always keep this line if we can always keep this line of food productivity growing faster than the population and time will tell whether our populations can become I guess we could say developed enough so that they don't and it's execrable I can never say that word they don't always just keep growing maybe they do become a Japan or a germany situation in the world population especially if if we have a high rate of literacy eventually does level off so never it never even has a chance of hitting up against that Malthusian limit but thought I would introduce you to the idea and now you can go to parties and you can talk about things like like Malthusian limits and if you want to know what country and you know is maybe closest to the Malthusian limit right now and we've talked about this before but a good case example is something like mahadesh they are right now the most population density in the world they have 900 people per square kilometer and just to give you a sense of perspective that's 30 times more dense the United States is so if you took every person in the United States and turn them into 30 people in the United States that would give you a sense of how dense Bangladesh is and it's probably due to a certain degree that it's a very fertile land that's it's the River Delta of the Ganges essentially makes up the entire country but they do they've have in the past had famines they've gotten a little bit beyond that but still you do have major problems with flooding and resources so hopefully they'll be able to they'll be able to stay ahead of the curve