The cave goes back into the rock farther than the light will follow.

It opens in the limestone of a remote Alaskan island, far enough from any road or town that reaching it requires a boat and the kind of willingness to get cold and wet that the Southeast Alaskan coast demands of anyone who takes it seriously.

The water outside is some of the most productive in the world — herring, halibut, salmon, sea otters, harbor seals, Stellar sea lions, humpback whales moving through the passages between islands.

The forest above and around the cave is Sitka spruce and western hemlock, thick and dark and smelling of moss and salt.

The island itself — Prince of Wales Island, in what is now the Alexander Archipelago of southeastern Alaska — is cut through with fjords and inlets and waterways that make a map of it look like something spilled and never cleaned up.

The cave is called On Your Knees Cave, a name that comes from the physical reality of moving through its entrance passage.

You come in low and you work your way through the dark and you eventually reach the chambers where, for thousands of years before anyone now living was born, the earth kept a secret.

The secret was a man.

He is known today as Shuká Káa — a name in the Tlingit language that means, approximately, “Man Ahead of Us.” The Tlingit people of the Southeast Alaskan coast gave him that name after his remains were found in the cave in 1996, a name that honors both his age and his relationship to the living people of the region.

It is a name that carries the understanding that this ancient man is not alien to the Tlingit and the Haida and the other Indigenous peoples of the coast — he is ahead of them on the same path.

He died approximately 10,300 years ago.

That number — 10,300 years — requires a moment of stillness.

He was alive before agriculture reached most of the world.

He was alive before the first cities rose in Mesopotamia, before the pyramids of Egypt, before writing was invented anywhere on earth.

He was alive at the beginning of the Holocene — the geological epoch that followed the end of the last Ice Age — when the coastlines of the world were still finding their present shapes and when the great ecological transformations of the post-glacial period were still in process.

He lived on an island in the North Pacific, among the islands of what is now southeastern Alaska, in a world of water and forest and marine abundance that had been shaped by the specific geography of this coast.

And when researchers eventually extracted ancient DNA from his remains and analyzed it against the genomes of later peoples, the result was something that few had expected to find with such clarity: evidence that the people of this coast have been here for an extraordinarily long time — that the Indigenous peoples of the Northwest Coast represent a deep, continuous ancestry stretching back through the millennia to the very people who first settled this shoreline after the ice retreated.

The DNA suggested, with the precision that genomic science can achieve, a continuity of roughly 10,000 years on the Northwest Coast of North America.