Why, after all, do we die? Yes, there are technological remedies. There is the virtual life everlasting that is “uploading,” and we’ll see more of that; there is the bloody-minded persistence of medical science without limits, procuring a bespoke longevity for those who can afford or mandate it. But these Cambrians simply evolved out of death by natural causes.

So again, why do we die? Because each time our cells divide, we eat into the chemical caps at the ends of our chromosomes. And as we wear away these telomeres, we accelerate towards an end point where the grabby hands of our cells’ biochemical mechanisms can’t get purchase on them. They fumble and drop them until, giving up in disgust, they refuse to replicate any more. Even where such degradation fails to happen, we reach another sticky end: cancers, cells out-dividing their neighbours, hostile and uncompromising.

The trilobite descendants, or at least one lineage, practically sweat telomerase—rebuilding their battered chromosomes every time their cells divide. They still die like flies from predation—sooner or later something will get you—but built into their design is this truth: they don’t have to die. The philosophers that they will one day produce will never face the existential question that haunts us. The question of why, no matter how good the show, the curtain must always come down.

Their biggest challenge—the one that limits their size and kills them despite their genetic chicanery—is moulting their exoskeleton, when all that hard support turns soft. Grow large enough and the effort of shrugging out of their entire skin is eventually fatal. And that, surely, is the end of the road for the Cambrians.

Except for one lineage of trilobite descendants, still passably trilobite-like despite the intervening millions of years. These Cambrians moult their shells away in flakes, shedding pieces heavy with corralled bacteria and parasites, growing constantly without ever needing to discard their entire hard wardrobe in one go. They grow big; they grow old. Give them a few million years and they’re as big as whales in the sea, as big as elephants on land.

Big doesn’t mean smart, of course; ask any sauropod. But they achieve a kind of sentience around the time our own distant ancestors are exiting the sea. Their sentience is a strange thing, a personal thing. As they master their world, so they learn to avoid the countless deaths by misfortune that would otherwise cut short their lives. Communication between individuals arises from intellectual desire, not social need. Their technology, as it develops, focuses on self-modification and improvement, further taking the reins from mere brute evolution. They become masters of their own growth and shapes, changing themselves for new environments and purposes, growing their exoskeletons into the tools they need to unpack the universe.