This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
JamesV is obviously a supporter of these notions, otherwise, how could he have the nerve to demand of the Forum that we have any responsibility to respond to his cynicism and rhetoric? Discussing limits to population growth and sustainability of food resource are non-questions, and about as useful as trying to out-guess the forces of evolution.
Feel free to tell me what the absolute maximum sustainable human population is. Any time will do. You may assume that future humanity has the capacity to harvest every single kilowatt-hour that falls on the planet from the sun, and the capacity to use this at 100% efficiency to provide for the minimal basic living standard for all humans and no more.
I have an abiding faith in humanity, simply because we possess the unique asset of an abstract brain which gives us the power of visualisation, enabling anyone to contemplate what may be; and to act on that contemplation: thus creativity is born. ---
It is because we have this power of contemplation that we can react to, and amend our personal environment to suit our best chances of survival, and the Survival Instinct is paramount, it is 'hard wired' through our genetic structure.
Humanity is indeed underrated, but it is also capable of overestimating its own ability to provide. People in poor parts of the world have lots of kids so that those kids can provide for them in their old age. Other people are religious and engaged in breeding wars with people of other religions or atheists. The evolutionary survival instinct always says "reproduce exponentially", the fittest will survive. The fittest in the case of humanity being the ones with the biggest sticks. There is an ugly counterbalance to our instinctive compassion for others, and it finds its most horrific expression at times of shortage of resources.
For every species, giving birth is a very painful, exhausting, traumatic process; not to be repeated unless species survival is threatened.
Most species aren't sentient enough to know where babies really come from. Come on, a lot of humans behave as if they don't! Clasically, all animal behaviour is driven by the "four F's", Feed, Fight, Flee, and Reproduce. Animals are not interested in their own survival - their genes are interested in their survival for as long as it takes to make as many copies as possible. Humans are little different in this regard, and are certainly unique in their ability to use contraception. Animals have sex because, like humans, they enjoy it. Anyone who thinks otherwise should take a walk in the country.
Notice the fact that much of the western world's birth rates are below replacement norms, and the norm for humans is 2 to 3 at this point in time. To me, it is apparent that nature is at work here; our females, to whom giving birth is a painful and sometimes life threatening process are sensing that our population is a little too high. Their instincts tell them that they do not need to take unnecessary risks, so birth rates will stay low until death rates balance the equation. Or, if over-much immigration continues, indigenous birth rates could fall further to compensate.
Bring the standard of life in the undeveloped countries up to our levels, and the females of those countries will be able to take a much needed rest from the strife of child bearing. --- Malthus needed an education, not privilege!
I think this is over analytical but it's clear that economic development goes hand-in-hand with a drastic reduction in the rate of population growth - the USA being something of an exception (I suspect that has something to do with the fact that it's the only seriously religious country in the developed world and making new souls for God to send to hell or fill his heaven with is a sacred duty, even to protestants.)
Let's try to bring on the economic development of the rest of the world before its population becomes truly unsustainable.