Mohammad Ramzan can neither hear nor speak, and he has a childlike mind. But he knew his wife, Saima, was too young when she was given to him as a bride.

The 36-year-old Ramzan smiles, eager to please, as he uses his fingers to count out her age when they married. One, two, three . . . until 13, and then he stops and looks at her, points and nods several times.

The girl’s father, Wazir Ahmed, says she was 14, not 13, but her age was beside the point. It mattered only that she had reached puberty when he arranged her marriage as an exchange: his daughter for Ramzan’s sister, whom he wanted to take as a second wife.

His first wife, Saima’s mother, had given him only daughters, and he hoped his second wife would give him a son. But Sabeel wouldn’t marry him until her brother had a wife to care for him.

She would be a bride in exchange for a bride.

“We gave a girl in this family for a girl in their family,” Ahmed says. “That is our right.”

In deeply conservative regions such as this one in the south of Punjab province, the tribal practice of exchanging girls between families is so entrenched, it even has its own name in Urdu: Watta Satta, which means give and take.

A girl may be given away to pay a debt or settle a dispute between feuding families. She might be married to a cousin to keep her dowry in the family or, as in this case, married for the prospect of a male heir.

Many believe that their Islamic religion instructs fathers to marry off their daughters at puberty.

“If it is not done, our society thinks parents have not fulfilled their religious obligation,” says Faisal Tangwani, regional coordinator for the independent Human Rights Commission of Pakistan in nearby Multan.