daughters would begin binding their feet from about the age of 5–8 to achieve the ideal appearance. The tinier the feet, the better the social rank of a future husband. This practice did not end until the early years of the 20th century. China has had many customs tied to girls and their roles as future wives and mothers. According to one custom, a girl's way of wearing her hair would indicate her marital status. An unmarried girl would wear her hair in two "pigtails", and once married, she would wear her hair in one. Africa In some cultures, girls' passing through puberty is viewed with concern for a girl's chastity. In some communities, there is a traditional belief that female genital mutilation is a necessity to prevent a girl from becoming sexually promiscuous. The practice is dangerous, however, and leads to long-term health problems for women who have undergone it. The practice has been a custom in 28 countries of Africa, and persists mainly in rural areas. This coming-of-age custom, sometimes incorrectly described as "female circumcision", is being outlawed by governments, and challenged by human rights groups and other concerned community members, who are working to end the practice. Trafficking and trading girls Girls have been used historically, and are still used in some parts of the world, in settlements of disputes between families, through practices such as baad, swara, or vani. In such situations, a girl from a criminal's family is given to the victim's family as a servant or a bride. Another practice is that of selling girls in exchange for the bride price. The 1956 Supplementary Convention on the Abolition of Slavery, the Slave Trade, and Institutions and Practices Similar to Slavery defines "institutions and practices similar to slavery" to include: c) Any institution or practice whereby: (i) A woman, without the right to refuse, is promised or given in marriage on payment of a consideration in money or in kind to her parents, guardian, family or any other person or group; or (ii) The husband of a woman, his family, or his clan, has the right to transfer her to another person for value received or otherwise; or (iii) A woman on the death of her husband is liable to be inherited by another person. Demographics Scholars are unclear and in dispute as to possible causes for variations in human sex ratios at birth. Countries