CONTROVERSIAL when it began a generation ago, China's one-child policy is stirring yet more contention. Until recently most discussion in China has been confined to academic demographers. Many of them argue that the policy did little good when it began and is increasingly damaging now that the fertility rate is below the replacement level and China's population structure—the balance between young, middle-aged and old—is becoming so skewed.

This month the debate became political. A provincial official went public with a request to let Guangdong—China's most populous province, with 104m people—loosen the rules. Speaking to newspapers, Zhang Feng, director of Guangdong's Population and Family Planning Commission, said he had applied for “approval to be the leader in the country in the relaxation of the family-planning policy”.

China's one-child policy is a bit of a misnomer. In most cities couples are allowed only one child, but there are exceptions. Couples in which both partners are single children may be allowed two. Some parents are allowed a second child if their first is a girl or if they suffer “hardship”, a criterion determined by local officials. Minorities (such as Tibetans or Uighurs) are permitted a second—and sometimes a third—child, whatever the sex of the first-born (see map).

For all the attention that his appeal has secured, Mr Zhang's proposal is in fact rather modest. Under the relaxation he seeks, couples would be allowed an extra child if only one parent were a singleton, not both. In practice, this would apply to a relatively small number of people. Most young urbanites in Guangdong are likely to be singletons anyway, so the exemption would be mainly for “mixed” couples, that is those involving a marriage between a local and a migrant worker from a rural area.

Because requests to the central government are seldom aired in public, some people suspect Mr Zhang of opportunism. “He smelled the air and is making a move,” says one demographer. According to another, Mr Zhang reckons he will be seen as a hero no matter what. If his demand is accepted, he will have brought about reform; if it is rejected, at least he will have tried.

Whatever lies behind it, Mr Zhang's demand is significant both because it is an implied public criticism of the one-child policy and because Guangdong was always likely to be in the forefront of any campaign for change. The province suffers many of the worst problems attributable to China's population control, notably a grossly skewed gender imbalance among newborns. The combination of a strong cultural preference for boys and prenatal ultrasound imaging has led to couples identifying and aborting female fetuses so that their sole permitted child is male. This is a nationwide problem, but Guangdong has consistently had some of the worst sex ratios. Normally, 105 boys are born for every 100 girls. In 2010, Guangdong had 119 male babies for every 100 girls. Ten years earlier, the ratio was a shocking 130.

The province also has big worries about the balance between its working-age population and their dependants in the decades to come. Guangdong's boom has sucked in huge numbers of young migrants from elsewhere (children and elderly migrants are deterred from moving by the household-registration system, or hukou). But as economic growth spreads to new areas, potential migrants may opt to stay at home, leaving Guangdong's labour-intensive export industries vulnerable to labour shortages. This is a microcosm of China's broader worries about ageing and the coming rise in the number of dependants for each working-age adult.

Zheng Zizhen, a demographer at the Guangdong Academy of Social Sciences (GASS), says even a modest change would help. “Every couple, in Guangdong and all over China, should be able to have two children. But before we take a second step or a third step in that direction, we need to at least take a first step like this one.”

Most demographers think the one-child policy has imposed huge costs on the country. The 2010 census showed that population growth was even slower than expected, rising just 0.57% a year over the past decade. The policy has caused conflicts with ordinary people and been a target of intense foreign criticism, worries Peng Peng of GASS (who nevertheless worries about relaxing it too fast). The costs were highlighted recently by revelations of a long-running scandal in Hunan province, where officials are accused of brutalising parents who violate the policy by confiscating “illegal” babies and putting them up for sale in the adoption market.

Few expect significant reforms soon. The family-planning bureaucracy is a vast and entrenched interest group defending the status quo at all levels of government. Senior officials fear that any change would unleash a population boom, despite predictions to the contrary by most experts. With only a year to go until China's first leadership change in a decade, no high-level figure in the central government is likely to back significant changes now. “If the government has political reasons for not being able to change the policy, then there is nothing I can do,” says Zheng Zizhen. “I can only say that from a scientific point of view, it is clear the policy needs to change.” Guangdong thinks so, too.