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Population control is a delicate matter.
Witness the reaction to Sir David Attenborough's recent pronouncements on efforts to feed the starving of Africa.
The great television naturalist was reported in Britain saying that sending food aid to famine-stricken countries only avoided the more fundamental problem of population growth.
The world was ''heading for disaster'', and without action the ''natural world will do something'', he told UK paper the Daily Telegraph.
''What are all these famines in Ethiopia? What are they about?'' he said.
''They're about too many people for too little land. That's what it's about. And we are blinding ourselves. We say, get the United Nations to send them bags of flour. That's barmy.''
One of the first to jump on Sir David was Oxfam senior policy adviser Hannah Stoddart, who said he was wrong and that there was plenty of food to go around if only the world shared it more fairly.
Writer Robert Newman leapt on Sir David from a greater height, in an opinion piece for The Guardian, declaring: ''To wish to reduce the number of living, breathing humans on this planet is an obscenity''.
''You can say there are too many people in a lift (`eight persons max') but not on Earth,'' he bristled.
The problem was not too many people on the planet, but too few owning too much of it, Newman declared.
The Rev Thomas Malthus might have warned Sir David to steer clear, were he still alive.
The ''father of demography'' fired his most famous shots on the subject around the turn of the 19th century, opining that as agriculture could not keep up with population growth - this before the Industrial Revolution kicked in - population should be constrained.
He then went on to suggest that paying child allowances to the poor would only encourage them to breed, from which his reputation has never fully recovered.
And yet, what if there is substance lurking somewhere in Sir David's outburst?As it turns out, the Royal Society of London thinks there is and last year published a report on the matter, ''People and the Planet''.
Now New Zealand's Royal Society has invited one of those involved in writing the report, Nobel laureate Sir John Sulston, to share some of its conclusions.
The chairman of the Institute for Science, Ethics & Innovation at the University of Manchester, Sir John is about to embark on a ''People and the Planet'' lecture tour of New Zealand, during which he will present the Royal Society of London's findings.
In short, it says Earth is struggling with the 7 billion people it has now, so should nothing else change, the 9.3 billion predicted for mid-century could spell ''social, economic and environmental failures and catastrophes on a scale never imagined''.
Humans have already altered some Earth systems, in the examples of climate change and nitrogen cycles, and impacted negatively on biodiversity and ocean acidification, while the consequences of reducing fresh-water quality and poor fisheries management wait in the wings.
Written, as it was, by a lot of very smart people from the Royal Society, and elsewhere, the report avoids Ms Stoddart and Mr Newman's objections, by meeting them halfway, and takes a considerably more benevolent attitude to the poor than the Rev Malthus.
On the phone from the UK, Sir John says the report looks at the impact people are having on Earth and analyses that in terms of both population and consumption.
''The point being that people have tended to focus on either one or the other, rather than realising that, of course ... that it is a combination of the two.
"We have more people and we have more consumption, with the accompanying emissions, that are leading to climate change.
"So what we wanted to do was to review the situation in a thorough way and present it in a way that would be useful to policymakers, as a firm foundation of science and scientific evidence.''
''People and the Planet'' says consumption has been raised closest to an art form in the West, where ''per capita material consumption is far above the level that can be sustained for everyone in a population of 7 billion or more''.
''This is in stark contrast to the world's 1.3 billion poorest people, who need to consume more in order to be raised out of extreme poverty.''
Meanwhile, population increases are sharpest in poorer countries, where child mortality is higher, education levels tend to be lower and access to family planning is limited.
Average births per woman in the least developed countries is down from 6.7 in the 1970s to 4.1 today, but that is still more than twice the average of 1.71 for women in the most developed parts of the globe.
It is population growth in the poorer parts of the world then, that will account for many of the 80 million extra souls a year forecast this century.
One such country is Niger, which faces a ''future in which population increase outstrips the production of food and other necessities of life'' as its population doubles in the next 20 years.
Sir John says there was some nervousness about taking on the issue of population growth, borne out by the way in which Sir David was ''roughly treated'' following his interview.
Indeed, Sir David was an early member of the Royal Society team working on the report, before his filming schedule forced him to pull out.
But the society was keen to get population back on the agenda in a serious way, after an absence of almost 20 years.
The report notes a conference in Cairo in 1994 was the last major international forum to make the connection between population, environment and development when discussing sustainability.
''In fact, now this year there is more discussion about population, at least around here in the UK,'' Sir John says of the impact of the Royal Society's work.
Whether the issue will gain traction further afield is an open question.
''Developing countries, the G77, are extremely nervous about putting it on [the agenda],'' Sir John concedes.
''It is not regarded as a politically correct thing to have there, because people feel there is an element of coercion.''
Some in the First World who would rather not have the discussion cast it as a human rights issue - the right to have a family - while others see it as a religious issue, Sir John says.
One of the legacies of the Bush jun administration in the US, is a continuing scarcity of funding for family planning initiatives, which he puts down to the influence of evangelical churches on US government policy. In that worldview the promotion of family planning is interfering in an area that is not the preserve of man.
Given such resistance to the topic, why push on?
''It really is important to emphasise the situation of women, whose rights are certainly being abused in some of the very high fertility countries, where males are dominant and women are married too young really to become empowered in the way we are accustomed to in Western societies.
"This, I think, is a human right that trumps the other more general consideration. [Women] should be given the choice, not forced, but given the choice to space their children as they wish,'' Sir John says.
An estimated 250 million women, concentrated in the least developed countries, cannot get access to contraception for various resourcing, ideological and cultural reasons, he says.
And the longer the delay in addressing fertility rates, the more the population momentum builds.
While population gets top billing in the Royal Society document, it shares the stage with concerns about consumption.
Taken together, increasing global population and increasing consumption - as developing nations chase the lifestyles of the developed - ''has implications for a finite planet'', the report says. Unwanted impacts and feedbacks are growing alarmingly, including climate change and species extinction.
''The thrust of our report, really, is that one must not separate these considerations of population and consumption,'' Sir John says.
''If one tries to treat them separately, you really do get a nonsense because you are not dealing with the real issue.''
So while population is stabilised by a combination of family planning initiatives, raising the world's poorest from the extremes of poverty and empowering women to make decisions about their own fertility, those sections of the globe where consumption is most fierce, are being asked to think again.
''Very importantly ... we end up with the last three recommendations [of the report] and especially the final one saying that we really have to alter our socio-economic systems,'' Sir John says.
The final recommendation reads: ''Collaboration between national governments is needed to develop socio-economic systems and institutions that are not dependent on continued material consumption growth.''
''In this final recommendation, nine, we are saying very explicitly, as others have, but we are emphasising it, that GDP as it stands is a very bad measure for human competition and success,'' Sir John says.
''The system of competitive GDP that we have is driving people to increase material consumption. We know this.
"All our governments are imploring us to go shopping more, to use more, to burn more fuel, the energy companies are encouraging us to buy their fuel, and so on.
"The reason is very clear, it is because this is the only way we know how to run societies.''
GDP, or gross domestic product, the report says, measures the market value of everything without capturing much of what is valuable in human life and undervaluing natural resources.
''Nobody wishes to see a reduction in their standard of living, but wellbeing can improve without growth in GDP,'' it says.
On the other hand, material consumption does not necessarily lead to positive development and is not always necessary for human development advances.
It would be imprudent to trust the invisible hand of the market to guide humanity away from environmental disaster, the Royal Society continues.
"As natural capital is absent on most balance sheets, it is being depleted without sufficient regard to the full long-term costs, and there is insufficient market pressure to develop substitutes.
Finding an alternative way forward must be an international effort, the Nobel laureate says: ''no-one country can stand aside from the rat race''.
People work harder and consume more unless all agree to work less hard and consume less, the report notes. The difficulty is finding a mechanism for encouraging such an agreement.
''It is a very big argument,'' Sir John acknowledges. Not least for political leaders trying to sell a message of less to the electorate.
''And nobody has found the formula yet.
"That's why we thought it important to put in our report because what people expect scientists to do is simply to say, oh, there will be new developments and this will, for example, increase our food supply, with different crops, for example.
"Or we do better engineering and water recovery and we have better water supplies. All of those things are fine, but if we do not join them with social change we shall just fritter them away as we are doing at the moment.
''That is not to say we should all wear hair shirts and damp down all human aspirations, but we do not need to be [consuming] as a sort of national duty,'' Sir John says.
''It is not meant to be a message of gloom by the way,'' he hastens to add.
''A call to arms certainly. But it is offering a way forward, which just working on the treadmill will not.''
The full Royal Society report ''People and the Planet'' is available at http://royalsociety.org.
The Royal Society recommends
Bring the 1.3 billion people living on less than $US1.25 per day out of absolute poverty and reduce inequality.
Stabilise then reduce material consumption in the most developed and emerging economies.
Promote and support reproductive health and voluntary family planning programmes.
Include demographic changes in economic and environmental debate.
Governments should realise the potential of urbanisation to reduce material consumption and environmental impact through efficiency measures.
High-quality primary and secondary education for all the world's young.
More research on the interactions between consumption, demographic change and environmental impact.
Governments should develop comprehensive wealth measures and begin natural asset accounting.
Develop socio-economic systems and institutions that are not dependent on continued material consumption growth.
Sir John Sulston will give the lecture ''People and the Planet'' at the University of Otago St David St Lecture Theatre on Thursday, October 10 at 7pm.
Tickets available from www.royalsociety.org.nz/planet.