Abdel's parents wanted him to go to school in Nouakchott, 300 miles to the west of the sandy plateau where they raised goats and camels. He was assigned a tutor, an eccentric European man with chunky glasses and an Afro, as Abdel recalls. The man required Abdel, at about 12, to go to Nouakchott's French Cultural Center every day to do extra reading.
Hesitant at first, Abdel soon dove into every book he could find. He started with French comic books like "Asterix." It wasn't long before he was picking up volumes about the French Revolution.
In a book on the subject of human rights, pulled from the library's shelves almost at random, Abdel found the idea that would alter his life forever:
Men are born and remain free and equal in rights.
Abdel read the line again and again.
"I started to ask myself if lies were coming out of this book," he told us, "or if they were rather coming out of my very own culture."
Once this seed -- a question that would undo his entire world -- had been planted in his mind, he couldn't stop it from growing. By 16, he returned to his family's nomadic settlement in the desert to tell his slaves that they were free. He was shocked by their response.
They did not want to be free, he recalled. Or they didn't know what freedom was.
His mother told him to stop being silly -- that the slaves needed the family to take care of them and that this was the natural order of the world, the way it always would be.
But Abdel was becoming ever more set in his belief that slavery was wrong -- that the rights of his slave, Yebawwa, were no different from his own.
In his early 20s, Abdel organized a community of young activists, most of them light-skinned like him, who began to debate the merits of the slavery they'd grown up with and had, in fact, perpetuated. They sat on sand dunes late at night -- in secret, for fear they would be found out by the government, which officially abolished slavery in 1981 but allowed it to continue. There, they discussed ways to end the practice that was so ingrained in their culture.
It was through these conversations that Abdel met Boubacar Messaoud.
The men came together on a rooftop in 1995, under a midnight sky of desert stars. In muffled voices, they plotted the founding of the abolitionist organization called SOS Slaves. It's one of the few groups fighting slavery in Mauritania today.
And it would liberate Moulkheir.
Boubacar still lives in the concrete compound that served as the meeting place for that first rooftop discussion about SOS Slaves. The night we interviewed him, we walked a circuitous route to his house, turning down sandy alleys and doubling back to check for followers. We slipped through the metal door that serves as the compound's entry around midnight, with only a sliver of the moon hanging in a charcoal sky. We found Boubacar, an imposing figure with strong shoulders, ebony skin and a snowy goatee, reclining in his living room.
An evening breeze sailed through the open windows as he told us about his life as the son of slaves in southern Mauritania, near the country's border with Senegal. Even though the master had granted his family limited freedom before Boubacar was born, he still grew up working in the man's field, he said, and the master took a cut of the crops they produced each year. This may not have been literal slavery, but it wasn't substantially different. "In that period, I could still feel that I was a slave," Boubacar told us, "that I was different from other children."
One important distinction: He could not go to school.
The master would not allow it, and his parents weren't going to take up the issue. This is something Boubacar never understood. So at 7, the same age Abdel selected his slave, Boubacar went to the local school even though he wasn't allowed to be there. An administrator saw him standing on the steps of the schoolhouse crying and, out of empathy, Boubacar told us, allowed him to attend.
Education would change Boubacar's life, just as it had changed Abdel's. Once he started reading about life outside his tiny world, he grew dedicated to the idea that all people -- including those in his family -- should be free.
Years later, he would find an instant ally in Abdel, the former slave master. This collaboration - between two men from opposite ends of Mauritania's rigid caste system -- would become the inherent power of SOS Slaves.
"If we fail to convince a maximum number of whites and a maximum number of blacks" that slavery is wrong, Boubacar told us, "then slavery will not go away."
Together, they developed a method for fighting slavery in Mauritania.
Step one was to interview escaped slaves and publicize their stories. The thinking: If a person knows slavery exists, how could they not want to fight it?
Step two was to help slaves gain their freedom. This was trickier, Boubacar told us, because a slave like Moulkheir -- the woman whose child was left outside to die -- must decide she wants to be free before SOS can do anything to help.
Scholars find many similarities between modern Mauritanian slavery and that in the United States before the Civil War of the 1800s. But one fundamental difference is this: Slaves in this African nation usually are not held by physical restraints.