Born in the PRC

But continuing public resistance forced the Party to modify the one-child policy during the 1980s and beyond. Most rural provinces were allowed to operate under a 'one-and-a-half child' policy - allowing a couple a second birth where the first child was not a son – while several provinces permitted two births per rural couple. Even with this relaxation of official policy, however, about 40 percent of births in 1988 were still classified as 'illegal'.

By 2007, China claimed that only 36 per cent of its citizens were limited to having one child. This was partly due to new rules allowing couples to have two children if they had both been only-children.

As for China's claims its one-child policy reduced numbers by at least 400 million, many remain skeptical. They argue it assumes that without it national fertility rates would have remained high, ignoring the impact of demographic transition arising from economic development.

Nicholas Eberstadt, a political economist with the American Enterprise Institute, recently described the policy as the 'single greatest social error in human history' in the Wall Street Journal.

"Rather than focus on undoing the inefficiencies of their Maoist economy, they blamed abysmal productivity on the child-bearing patterns of their subjects. The outcome was involuntary birth control, promulgated through a vast scheme of quotas and an army of family-planning agents. This was socialist 'scientism' – ideology masquerading as science – of the highest order."

As for the economic impact, China's labour force peaked in 2012 at 940 million and fell to 930 million last year. About 29 million workers could be lost in the decade to 2020. But adopting a two-child policy at this stage of the demographic cycle – its effect will not be felt for many years - will not improve an economy currently under pressure.

Slowing growth is inevitable over coming decades. But according to Chang Lui of Capital Economics China and others, it will not be driven by labour force shrinkage but slower productivity growth because of 'diminishing room for catch-up with richer economies'.

There is another perspective too. China wants to appear more liberal, but remains determined to maintain control over procreation. Who would want to re-train a vast army of population-control bureaucrats, lose fines for out-of-quota births and so on?

While the two-child policy seems to be more than a baby-step in the right direction, the state will still haunt the bedrooms of its citizens. So despite talk of reform, the Chinese government, seems unwilling to relinquish completely this instrument of social control.

As for the policy's numerical impact, it could be small. Public response to a major policy change two years ago saw only 1.5 million couples out of an eligible 11 million apply to have a second child by mid-2015.

In any case, it will be dwarfed by much bigger changes elsewhere on the global demographic stage. Humankind's numbers will grow by more than the UN Population Division's previous estimate of nine billion by 2050, according to its latest 2015 Revision of World Population Prospects.

The current world population of 7.3 billion is increasing by 83 million a year. It will reach 8.5 billion by 2030, 9.7 billion by 2050 and 11.2 billion by 2100, assuming UNPD's medium variant projection is accurate. If, however, a higher fertility rate prevails this century, there would be 16.6 billion people by 2100, assuming another global doubling is supportable.

India will overtake China as the most populous country in seven years. Africa's population will double in the next 35 years. By 2100, almost 40 percent of the world's population will live on this one continent. By then, India could have a population of 1.6 billion, with China's numbers projected to decline by about 30 percent to one billion people. However, an increase in average fertility of just 0.50 children per woman this century - as assumed in UNPD's high variant projection – would see India with 2.6 billion people in 2100, and China with 1.6 billion.

Yet there are at least 61 prominent Australians who fervently believe their country – with just 24 million people – has a right and a duty not to sell coal or coal assets to either of the world's two demographic behemoths. Based on adodgy hypothesis, they want instead a 'moratorium on new coal mines, as called for by President Anote Tong of the Republic of Kiribati, and Pacific Island nations', who account for less than 5 percent of humankind.