We have quite enough food in the world; we just have too many humans. Population researcher Hans Rosling is famous in stating that what we just need is a rise in living standards in the developing world to stop the rise in population. Hans Rosling has shown that a rise in living standards will bring with it a drop in number of children. History shows that number of children produced per family has always slowed down hand in hand with any rise in the living standards.
However, the process works even more clearly the other way round. Living standards tend to rise when the number of children per family does actually drop. I don't mean that Hans Rosling would have his facts wrong. I'm just suggesting that the thing works both ways. The other factor is a necessary and vital component of the other, and it is very difficult to have the other without the other too.

Admittedly everyday logic is not always the best tool in a questions concerning the inner workings of economy, but here it works in a quite straightforward way. The more people there is to share of the accumulated wealth of a nation, the less a single individual will get. Of course, the accumulated wealth is just a small part of the equation, as the important thing in a modern growth-based economy is producing new wealth. One can well suggest that the more there are consumers, the more they will produce and buy and make the economy go around faster.
However, things are not so easy at all in economics. A very important thing is that the more there are new children, the more resources must be used to educate them. In fact, the share that an individual will get of the resources used for education can get smaller when there are more children sharing the limited resources. So, when more children are being born, they will get less education individually and they will be less useful for the general economy.

Eugène Delacroix, The Women of Algiers, 1834, the Louvre, Paris. - Wikipedia

Even bigger thing is that in a situation where the growth in available work-force greatly outnumbers the available openings in the workplace, the price of work will not rise. An eagerly hidden fact is that the average income of the workers in the western world has risen for a great deal during the last century largely because there has been the scarcity of labor.
When there is no oversupply of labor, employers simply had to pay more to attract workers. This is largely because the rise of easy to use and safe methods of population control greatly diminished the flow of new workers to the markets. However, also the modern western mass-markets were born when there rose scarcity of labor. On the other hand, the work that was done by the labor-movements was a major factor for the rise in the pay of the workers. It rose ultimately to such levels that they could finally start consuming.

The great paradox of capitalism is that, in the end, it needs workers who have enough money so spend to be create a market for the very goods that capitalism produces. However, a single capitalist is never willing to pay for its own employees more than it is forced to do.
A single enterprise looks at only after its own narrow interest. An entrepreneur will pay just as much for his workers as he is forced to do by the current circumstances. The sole aim of any enterprise is, after all, to produce as much money as possible for its owners. A company always simply exists for the sole purpose of creating profit for its owners.

A very important factor in this situation is the impact of trade unions and also of leftist political movements. Unions are, however, in a major disadvantage in a situation where there is a large oversupply of workers available. This 9s is currently the case in many parts of the developing world.
The rapidly expanding population in third world countries is, in fact, one of the greatest obstacles in achieving any kind of economic, social and political progress in these countries. Economy is a immensely complex thing, and population is only one factor in the complex equation. However, it affects so many other moving parts of the economy that it may be one of the most wildly underestimated and universally not-openly-spoken of factors of economy.

There are many different reasons for this rejection. One important thing is that it does not fit into a political agenda of the "anti-imperialist" movement. Considering over-population as an important factor will seemingly in their mind diminish the importance of their ideological agenda of imperialism and colonialism as the major or even sole cause for underdevelopment in the Third World as they so often seem to claim. "Anti-imperialists" seem to fear that taking local factors into account would undermine their overriding single Great Idea.
The sad fact is that these "anti-imperialists" have all too often wielded an unholy alliance with religious leadership. A sad fact of life is that many religions even totally oppose all forms of population control. Some religious leaders just could be very interested in growing their support-base. One could well suspect that they do in practice oppose population control for this simple reason, even if no real doctrinal reasons for this opposition do not exist.

This highly unholy alliance has produced a situation where even discussing population control as a remedy for the economic ills of Third World seems to be all too much for many. When ideologies like religions come to play very simple and practical matters can become more complicated.
The rise of China after the madness of strict Maoism was possible largely because of the one-child policy. This policy was one of the cornerstone on which the current rise of China is based. However, fast and concrete investments in population control would produce results that would outshine the results of all of the current aid to the developing world. The developing countries simply would soon have more to invest to make the future better for every child that is born. The road of these children to respectful and full life would be made much easier than it is now.

(This piece was completely refurbished on 23rd of October, 2012)

http://www.ted.com/talks/hans_rosling_on_global_population_growth.html