I think the competitive model for species evolution and resource consumption that is applied to all animals in nature doesn't hold true for humans. After all it is our dynamically shifting co-operative nature that allows us to form society, and to support the vast population that we currently have. The simple fact of the matter is that the reason more children are born and survive is because our technology is capable of supporting them. The tech level won't decrease any time soon, and so we will be able to support further increases to the size of human population without too many difficulties. The fears of overpopulation in the eighties didn't factor in the extreme efficiency of food corporations, or the closer ties in the global economy: both of which make the die backs and other overpopulation issues less likely.

The lack of space issue can be dealt with, well, SPACE. I believe that long before we run out of room and resources here because of a burgeoning population, there will be colonies on the other planets in this system, notably Mars. To give you some idea of how ridiculous this particular argument is, it is worth noting that the entire population of the world (thats right, all 6 billion of us) can fit neatly with standing room on the Isle of Wight. A very very small island of the coast of the UK. I therefore don't believe we will be running out of room soon.

The waste issues can be dealt with by appropriate environmental policies and attached enforcements. People need to learn how to recycle anyway, and if they want their children to live good lives then the incentive is there.

As for the argument that overpopulation would stress the current political and social, and economic systems. I say, bring it on. We need change, and radical change at that, I do not see how the human race can continue to strive with precisely the values it has at the moment, they continue to evolve and we alongside them. The systems will change to accomodate more of us. More of us means more geniuses, more awareness, more civilisation, and more work done on ourselves and our environment.

It is possible to fit 6 billion people into the Isle of Wright with room to spare. In fact, you could fit 27 billion people into a cube one mile by one mile by one mile.

Only catch is, each person would have 12 cubic feet, or six feet by two feet by one foot. Now imagine that you're at the bottom of the cube.

What is overlooked time and time again in the "you can fit x people into ____" argument is that just because you can fit a population into an area doesn't mean that area can support it. The most common example is Texas, at least in America. But what about arable land?

"If you divided the world's 6 billion humans into Texas's 261,914 square miles, each person could claim .028 acres of land. It is obvious, however, that the land in Texas, (or even the land in North America for that matter), would not be able to sustain these people. Resource experts say a minimum of 0.17 acres of arable land is needed to sustain a person on a largely vegetarian diet without the intense use of fertilizers and pest controls.

An estimated 253 million people currently live in countries with scarce arable land--which have on average no more than 0.17 acres available per person -- and this population is expected to at least triple by 2025 if current trends continue. Only 11 percent of the Earth consists of arable land, and that area is rapidly diminishing due to erosion, salinization and a decline in the practice of fallowing land."

http://www.zpg.org/Reports_Publications/Reports/report83.html

As for space, let's say people will be transplanted to Mars by 2030. The world population will be 8.1 billion by then (http://www.census.gov/ipc/www/worldpop.html). In order to maintain current population levels, we would have to devise methods to transplant 2 billion people within thirty years. At a round trip of two years to get to Mars at the optimal revolution of the planets around the sun, with 50,000 people making the trip each time, you would need to make 40,000 trips before you could transplant 2 billion people, over the course of 80,000 years, at which point you might see H.G. Wells and his time machine where London once was.

What's my point? Look for answers close to home. Keeping your head in the clouds can be fun, but not always productive. Rather than trying to find solutions to the effects of overpopulation, one should try to find solutions to the causes of overpopulation.

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For those interested, let's say we started sending people now and wanted to make sure we were at 6 billion people in 2030; the number of trips that could be made is 15, at 133 million people per trip. The maximum number of people to send at today's capability per ship is about ten. That's 13 million ships being sent every two years, plus enough food and water to feed people for the ten to twenty years it would take to allow for food to be grown on Mars. Put the cost of sending each ship at 20 billion dollars (http://www.miami.com/mld/miami/news/world/3607347.htm), not counting the cost of constructing habitats on Mars, and not counting the cost of constantly sending supplies (and even then 20 billion dollars is very modest). That's 260,000,000,000,000,000 dollars (two-hundred sixty quadrillion dollars) every two years, at a total cost of 3,900,000,000,000,000,000 (three-quintillion nine-hundred quadrillion dollars) over the course of thirty years. If every person in the United States (287 million as of this year) were to pay an equal amount towards this, the cost over thirty years would be 13 and a half billion dollars, each.

The population only grows based on what the environment / technology can currently support. If the environment sucked or technology sucked, then population would be naturally low. If both rocked, then the "ceiling" of population would go up, leaving a lot of potential "empty space" for new people to be born into.

If the population were already at its "ceiling" then for every person born, there would already be another starving - in other words, the population would already have stopped growing.

The only things that can cause mass starvation are things like sudden changes that make the environment suck, or the destruction of technology, or the misuse / idling of productive resources (such as those caused by economic depression or civil war).

For each of those possible "world-ending" scenarios, there are actions we can take:

1) "Protect" or even "improve" the environment, at least with respect to human survival. Things like increasing the amount of arable land, clean water, learning to grow food on the oceans like when we first learned to grow it on land, etc.

2) Improve technology and spread it around (the more people that know it, the harder it is to forget it). Sure the population may be growing, but if it's an educated population, then they'll work together to develop new ways to sustain even more people. Arg! Human beings are a cancer! =) It's more than just human beings taking up a greater percentage of the biomass or increasing the overall amount of biomass, but eventually I see technology as one that will take the elementary building blocks of organic compounds from all kinds of sources, and making organic compounds out of them.

3) Economics and civil wars are obviously highly political issues. If resources are idle or misused because of mere accounting or other reasons and people are starving, then they should just get over their ideology and start using the idle resources. It is the ideology itself that is not fit to survive.

I see concern about "overpopulation" mostly as racism. It seems many just don't want Third Worlders to be "breeding" - well, if they were already starving, the kid who was just born would immediately starve anyway - the fact that populations grow in Third World countries just means the world can support them.

As for those that believe overpopulation is mainly a problem of consumption in wealthy countries, indeed I agree that capitalism is a big part of what makes population growth a threat to human survival: see Demand is not measured in units of people, it is measured in units of money and the discussion of the role consumerism plays in our incentive system.

Indeed we may consume everything and then die out after all resources are gone - but that would be a problem of political and economic policy, which we have full control over. To me, if you wanted less depletion, more efficient usage, or more new and as yet undiscovered sources, then all the more reason to get involved in political and economic policy instead of, say, reading about celebrities or playing chess (not that I don't like chess myself).

To me, the better technology there is, the more "resources per person" there is. Thousands of years ago, they didn't have solar, nuclear, wind power, or even agriculture, so "resources per person" was low. Thousands of years from now, they will have who knows what kind of technology (maybe even man-made stars), so "resources per person" will be very high. The key difference is the amount of technical advancement.

As gate discussed, this world, like any closed system, is self-balancing. There is no argument about that. Fundamentally, the world as a system only has sunlight as input, and the output is limited to heat and other various forms of radiation. If you want to get picky, the occasional ball of space junk we decide to catapult can be listed as 'output', too.

The part of gate's logic (as well as Jaez's points in the original write up) that troubles me is that humans have acquired the ability to destroy much faster than natural forces are able to create. Furthermore, as much as there are very smart people in every field, the average person is ignorant (and often indifferent) to the effects of their actions. Because of this, we as humans may not follow the same self-balancing pattern of other historical predators, and we risk bringing both ourselves and the planet we are on to a lifeless ball of ash.

I will admit: throughout the course of the evolution of life so far, every predator has either found a balance with the surrounding life around them. Alternatively, they consumed all they could, starved themselves out, and were wiped into extinction. From there, the remaining ecosystem replenishes itself and continues as usual.

The trouble with humans now is that we don't consume just a small fraction of the ecosystem. Our 'every part of the buffalo' approach to consumption means that if we don't find a balance with the surrounding ecosystem, nearly everything is being taken down with us. We are not simply wolves who have taken all the deer before starving. We have taken the deer, trees, and every other animal, small and large. What is left to recover when we succumb to our own stupidity? These troubling questions lead me to believe we only have one chance at this self-balancing model. We must take it seriously.

Humans are plagued with a sense of entitlement as well as a natural hubris. We think we deserve the best. More importantly, we think we are entitled to it. "I NEED a car", "Pass the steak (I want a third helping)", "Think of the children!". It is this mix of natural human consumption mixed with the feeling we are entitled to consume more (and spawn more children, which will require even more consumption) that will be our downfall. In the end, there are only so many acres of land to find food on. hramyaegr touched on this point earlier. Even when there is not enough land to feed everybody (which there very well may not be right now), our sense of entitlement will keep us breeding and demanding more. The trouble is, nature works on it's own time. We can't bully it. All that's left then is for us to grow up, or pick nature to the bone, effectively destroying us all.

I fear for our ability to grow up as a collective society and act responsibly. I really, really do.

Overpopulation won't be a problem -- one day. As populations age they slow down their growth, until, it seems, they actually start to shrink. We don't know if this will hold true for every country, but it is happening in Europe, North America, and Asia. This is largely because educated women who are able to take control of their reproduction will on average have fewer children.

Population growth by country:

• Estonia: -0.632%
• Ukraine: -0.632%
• Russia: -0.467%
• Hungary: -0.257%
• Japan: -0.191%
• Germany: -0.053%
• Italy: -0.047%
• United Kingdom: 0.279%
• United States: 0.975%

These numbers are from the CIA World Factbook, updated 2009. And yes, those minuses do mean a negative population growth. The USA and the UK are higher than other developed countries largely because they have so many immigrants from less developed countries, and these immigrants have higher birthrates than the WASPs Yuppies. Much of Asia has a growth rate of less than 1%, including China (at 0.655%). All of these countries (and many others besides) are showing a general trend of decrease in the rate of population growth, and it is predicted that in the next few decades the only thing keeping them from negative growth might be immigration.

Of course, there are many countries that have people starving, dying of malnutrition and poor water supply, or being killed over things that are in short supply because of overpopulation and poor resource management. The developed nations pump billions of dollars of aid into these countries, and they are making some headway. You can help; there are many organizations that would be happy to take your money and give it to someone in need. (Ad for PATH goes here).

However, you, personally, are unlikely to see a world in which there are no countries with overpopulation. Your grandchildren will likely live to see such a world, although if that world has flooded or had the oceans poisoned there will surely be starvation for many decades more, as the excess billions die off. Eventually, though, we will reach sustainable population levels.

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As a sidenote, world population is measured in billions, so sending people into space colonies is not likely to become a useful strategy. Sending one billion people to Mars will likely remain unfeasible. Sending one thousand people and waiting for them to multiply is a much more reliable (and affordable) method of settling the universe.