By allowing all couples to have a second child, the authorities could also reduce the demographic risks such as shrinking working-age population and the increasing gender imbalance. History tells us that a society of two-children families is more suited to balanced demographic development.

Since 2000 China's average fertility rate has been around 1.4, which is rather low. China faces a great challenge due to its growing aging population and proportionately declining youth population. Moreover, gender imbalance, too, is a serious problem - for example, tens of millions men cannot find a wife. Therefore, by further easing the family planning policy, the authorities will not only help many families cope with the loss of a child, but also reduce the demographic risks.

Allowing all families to have a second child could also help China achieve balanced demographic development. The country seems to have fallen into the trap of low fertility rate. Many young couples, despite being the only children of their parents, are unwilling to have a second child because they have to take care of their aged parents. Some don't want to have a second child either because they are too focused on their careers or cannot afford to pay for its education and other needs.

Since the 1990s the cost of bringing up a child in China has increased steadily, forcing a lot of couples to decide against having a second child. So further easing the family planning policy will not lead to a population boom, which the authorities fear, because demographic development always moves in waves. Even in rural areas where traditionally people tend to have more children, the fertility rate is only 1.6.

China's childbearing-age population as a proportion of the total is on the decline, and if the existing family planning policy continues, China will be hard to achieve sustainable demographic development. So, the family planning policy should be eased to allow all families to have a second child for the sake of sustainable social development.

The author is a professor at the Population Research Institute of Peking University.