“It challenges us to question: What does it even mean to be human?” This declaration comes from Agustín Fuentes, an anthropologist, at the beginning of “Unknown: Cave of Bones,” and it becomes a refrain throughout this documentary. It’s the kind of statement that can read as trite and grandiose — particularly in the context of a science program — but here it has a gravity that is reinforced and viscerally felt over the course of the film.
Directed by Mark Mannucci, “Unknown: Cave of Bones,” focuses on a recent expedition into a South African cave that contains skeletal remains of the ancient human relative homo naledi. The archaeologists’ findings lead them to conclude that the naledi, who may have existed as far back as 335,000 years ago, ritualistically buried their dead, which was previously unheard-of for such an ancient species.
As the team unearths evidence, the documentary offers a ripe window into the process of scientific discovery. Most of all, the film offers an affecting story of a species told through a single cave, where according to researchers including Fuentes and the paleoanthropologist Lee Berger, the naledi would risk life and limb to memorialize their dead.
In this sense, in the experts’ telling, to challenge what makes us human is also to remind us of the most basic hallmarks of ourselves: to love, to grieve, to honor a life and to hope that we’ll see each other again.
Unknown: Cave of Bones
Not rated. Running time: 1 hour 33 minutes. Watch on Netflix.