Let's not kid ourselves. This is a race issue. Middle class white people are too caught up in our culture of gathering possessions and indulging in hedonistic sex to want to reproduce. For every middle class woman who is voluntarily childless, there is an illegal immigrant family that has four.

Oh for Crikey's sake what does any of what you are saying have to do with the arithmetic of the exponential function. Talk about setting up a straw man. Or is it a darkie man?

Nature doesn't give a rodent's anal orifice whether you run the experiment with bacteria in a petri dish or on the planet with human beings. Theoretically it should even work with little green men with purple antennae. When the nutrients run out the growing population crashes end of story.

For fun you might get your self a chessboard and put one grain of rice on the first square then put two on the second square then four on the third keep doubling the number of grains until you get to the last square and let me know how many grains you end up with. Cheers.

Differential resource access between the overdeveloped and underdeveloped nations is a "hard problem" (a phrase apparently used by physicists to indicate a problem that's insoluble).

It's not intrinsically a race problem, and those who mention it are generally just commenting on observed facts with no value judgment implied. The fact that the overdeveloped nations are predominantly of white European ancestry while the underdeveloped nations are not, of course leaves us open to such charges on the basis that "commenting is condoning" or some such foolishness.

However, to view the world as a single undifferentiated mass of people (or a single mass of aggregated consumption) is less useful than an analysis that factors in the situations of individual nations as well as the role of national boundaries. I like to think of national boundaries as cell walls. A cell has relatively full control over what goes on inside them, but the transmission of information and resources across a cell wall or national boundary to influence neighboring cells is highly regulated and flows are restricted.

Thus when someone says "We grow enough food to feed everyone int he world, the problem is one of distribution," or "There is enough energy produced on earth today to give everyone 2.5 KW" they are ignoring the fundamental constraints imposed by the way the world we have created actually works. We ignore those issues at our peril. Recognizing them isn't racist, it's realistic.

Acknowledging that overpopulation is a problem does not mean we think it's the only problem. And acknowledging that it's a problem doesn't mean we endorse coercive means of population control.

What you are assuming is that the couple in question actually wanted six kids. I don't think there should be mandatory limits on childbearing (at either end of the spectrum, which is why I'm vociferously pro-choice). But we have had the ability to reduce unintended pregnancies by a factor of 1000 for the past 50 years (the pill, in addition to more recent birth control advances). The fact that we have not made the ability to control family size a basic human right is racist, classist, and a gross human rights abuse.

If you truly want six children, (for your own reasons and not because of religious or social pressures) I won't argue with you. And I won't do anything that would limit your free choice. I will certainly do everything I can to give you and your children the highest quality of life possible.

But what we're ignoring is that a good proportion of our population growth is due to unaffordable and unwanted pregnancies (in every class and in every race). I think all people of conscience would support reducing this burden on women and families.

I do understand the fear of eugenics. The US has a shameful history in this area. If there must be mandatory limits on growth, they should be on consumption. But we have an opportunity to decrease the stress on the planet AT THE SAME TIME as enhancing human rights, and cutting off discussion before we even have a chance to state our proposals is not helpful.

Simplistic statements like this ignore several inconvenient facts. Yes, fertility rates are falling world-wide. But:

• The world's average TFR is is 2.6.
• By 2050 the UN expects world population to grow by 40% or so.
• We are already using more resources and producing more waste than the planet can support long term.
• 5 billion people live in countries with TFRs over 2.1.
• By 2050 the UN expects the population of those countries to grow by over 50%, to 7.5 billion.
• These nations are (coincidentally?) the poorest on earth. Their growth will pose enormous social, economic and political difficulties in a world of declining oil and gas supplies, changing climate and essentially static food supplies.
• These nations are all trying their best to expand their material standard of living (as we all are).

To me this set of facts adumbrates a looming demographic catastrophe.

And where are these birth rates falling? It's directly proportionate to access to birth control and health care. People are willing (even eager) to control the size of their families, what they are lacking is the necessary tools.

"Birth control: the biggest silver BB"

We would do well to understand things the way you have framed them. The exponential problem is twofold. Population and lifestyle.

(So much for the "all that people have to do is adopt western lifestyles and fertility rates will come down problem solved" hypothesis)In my view western lifestyle is the larger immediate problem over population.

Now that billions of Indian, Chinese and others are on the verge of copying 'western' standards of consumption the alarm bell sounds. Where was that sense of urgency before? Malthus, The Club of Rome and Ehrlich had warned us but we paid little mind. Since competition for resources today has reached critical levels it's a crisis.

That will continue until all 'western lifestylers' throttle back on overconsumption and fertility rates worldwide decrease further. Failure at either end means failure of the system.