(Michelle Kondrich/For The Washington Post)

Dorsa Amir is an evolutionary anthropologist and postdoctoral research fellow at Boston College.

Nearly 100 years ago, a team of archaeologists working in Greenland stumbled onto something strange: careful arrangements of brightly colored stones nestled into the frozen landscape. There was no mistaking they were intentional, the ovals of red and white pebbles, but what were they?

The team traced the formations to the walrus-hunting Thule people of the medieval era, the predecessors of the Inuit. And they assumed what archaeologists often assume, that the structures were religious in nature.

But they were wrong.

The stones weren’t talismans for hunting or warding off evil spirits. They were something arguably more wondrous: children’s playhouses.

The stones were the remnants of miniature dwellings that children had built to mimic adults’ structures. They even had small caches for storing imaginary meat and blubber, represented by the red and white pebbles.

The Thule children were doing what children have done for millennia: learning about the adult world through play. And the archaeologists were doing something that is all too common: underestimating the importance of children’s culture.

When we think about our hunter-gatherer ancestors, it’s easy to overlook the children. Even the exhaustive ethnographies that dot the anthropological literature tend to focus on adults — on their warfare, subsistence and marriage patterns, the busy lives they led.

But our understanding of who we are as a species is incomplete without considering childhood.

Childhood is unique to humans. Our primate cousins debut into the world after weaning as more-or-less independent juveniles. But Homo sapiens’ children stick around. Years after weaning, they are still in our care. This long period of dependence gives humans time to master the enormous number of skills we need to become successful adults.

For 99 percent of humanity’s existence, that meant being a successful forager. Children needed not just ecological knowledge, such as which plants were safe to eat, but also a wealth of social and technical knowledge — how to build a sturdy dwelling, with whom to cooperate.

To meet this challenge, we evolved something rather remarkable: a society-within-a-society composed of children, generating their own culture as they mastered the adult one.

While we can’t perfectly re-create the details of these child cultures — bones fossilize, behavior doesn’t — we can infer their existence from a variety of sources. We find their echoes in archaeological ruins, such as the Thule playhouses. Or we catch glimpses in old ethnographies, such as Bronislaw Malinowski’s amused observation of Trobriand Island children “standing often in . . . collective opposition” to adults. “If the children make up their minds to do a certain thing,” he wrote a century ago, “. . . the grown-ups and even the chief himself . . . will not be able to stop them.”

Some of us anthropologists are lucky enough to see children’s cultures in person among the few remaining small-scale societies in the world. In my own fieldwork among the Shuar of Ecuador, I watch play groups reshuffle throughout the day, just out of the adults’ sight. I see boys with small machetes mimicking work, girls showing younger siblings how to keep the fire alive.

We find commonalities among such societies everywhere we look, from the Arctic to the Amazon. Children spend their time immersed in child communities, age-mixed and sometimes gender-mixed, operating in parallel to and largely independent of the adult ones. The children learn as a collective, with younger kids following the models of older kids. Given the consistency of these characteristics, we can infer that these cultures of childhood are probably ancient, even pre-dating Homo sapiens.

Such consistent features of our evolutionary past leave enduring marks on our psychology. Our innate perceptual system expects a sun that lights the world from above. Our linguistic system expects language, even in the womb. Perhaps our learning systems function the same way, expecting a culture of childhood marked by independence and play.

Unfortunately, that culture is quickly slipping away.

In the past 10,000 years — a barely perceptible sliver of evolutionary time — virtually every feature of childhood has changed, particularly in industrialized societies. Instead of growing up in a mixed-age collective, our children spend most of their time indoors with same-age peers. Gone are the days of evading grown-ups: Constant supervision is expected. Recess, the last vestige of free play, is on the brink of extinction. I contributed to this myself as a camp counselor, shepherding kids to structured activities, convinced that by teaching them rules or settling their disputes, I was helping them grow.

I don’t think this anymore.

Children’s cultures didn’t evolve by accident. They served a function. In free play, children practice creative thinking and problem-solving. In mixed-age play groups, they learn from older peers and teach younger ones, meanwhile consolidating their skills.

Without understanding its evolutionary function, it’s easy to underestimate children’s culture. And through this pathological undervaluation, what we have effectively managed to do is slash and burn core features of childhood — the very roots of what makes us human.