Final answer:
An unintended consequence of China's one-child policy is disproportionate gender ratios, caused by the preference for male heirs and resulting in sex-selective practices.
Step-by-step explanation:
In 1980, China implemented an antinatalist one-child policy. One unintended consequence of the policy is disproportionate gender ratios. This was primarily caused by a cultural preference for male children, leading to sex-selective abortions and female infanticide. Consequently, the policy did not just slow population growth; it also changed the demographic makeup of the population, resulting in a significant imbalance between the number of males and females in China. The desire for a male heir in many families, combined with the strict one-child limit, intensified this issue.