Kenya's Samburu boys share a sacred bond. Why one teen broke with the brotherhood

The Science of Siblings is a new series exploring the ways our siblings can influence us, from our money and our mental health all the way down to our very molecules. We'll be sharing these stories over the next several weeks.

Paris Lekuuk is 15 years old. But he's standing in the third grade of a primary school in Northern Kenya – squeezed between 8-year-olds who barely reach his elbows.

The teacher is leading his classmates in a rousing rendition of a classic.

"Heads, shoulders, knees and toes!" she calls out.

The little kids sing back with gusto, "Knees and toes! knees and toes!"

Paris gives a shy smile and pretends to mouth the words. He doesn't speak English – or even Kenya's other, more commonly used official language of Swahili. Until a few weeks ago he had never set foot inside a school. In keeping with the custom of his people, known as the Samburu, Paris had been on a mountain, living in a band of boys.

The Samburu have kept cattle in this region for centuries. Teenage boys like Paris serve as the community's "morans," meaning warriors, charged with looking after the herds. During the dry season, when the grasses on the plains here wither, small groups of these moran boys spend months on their own – driving the cattle ever further up the highlands in search of the last remnants of pasture and water.

To survive, the boys rely on a bond that they say makes them closer than brothers. It's a sense of mutual obligation central to their Samburu culture – so strong that anthropologists and economists have come from afar to document its impact.

But it's a version of the sibling relationship that, with the onset of climate change, is increasingly under threat.

For Paris the consequence has been a break with