And in some of those comets were Earthborn bacteria. Only a few. But it only took a few.

Still the sun aged. It bloated to monstrous proportions, glowing red. Earth skimmed the diffuse edge of the swollen sun, like a fly circling an elephant. The dying giant star burned whatever it could burn. The final paroxysms lit up the great shell of gas and dust that lingered around the sun. The solar system became a planetary nebula, a sphere shimmering with fabulous colors, visible across light-years.

These glorious spasms marked the final death of Earth. But on a new planet of a new star, the nebula was just a light show in the sky. What mattered was the here and now, the oceans and the lands where new ecosystems assembled, where creatures’ changing forms tracked changes in their environment, where variation and selection blindly worked, shaping and complexifying.

Life always had been chancy. And now life had found ways of surviving the ultimate extinction event. In new oceans and on strange lands, evolution had begun again.

But it had nothing to do with mankind.

Exhausted, dust-laden, her body covered by a hundred minor scrapes, bruises and prickles, her baby cradled in her arms, Ultimate limped to the center of the ancient quarry.

The land seemed beaten flat, with the sun poised above, a great glowing fist. And at first glance there was no sign that anything still lived on this desert world, none at all.

She approached the Tree itself. She saw the big pendulous folded-over shapes of cocooned people, inert and black. The Tree stood there, silent and still, neither reproving nor forgiving her small betrayal.

She knew what she had to do. She found a folded-up ball of leaves. Carefully she prized the leaves open, shaping them into a makeshift cradle. Then she placed her baby carefully inside.

The baby gurgled and wriggled. She was comfortable, here in the leaves; she was happy to be back with the Tree. But already, Ultimate saw, the belly-rope had snaked into its orifice in the child’s stomach. And white tendrils were pushing out of pores in the cradling leaves, reaching out for the baby’s mouth and nose, ears and eyes.

There would be no pain. Ultimate had been granted that much knowledge, and comfort. Ultimate stroked the child’s furry cheek one last time. Then, without regret, she folded up the leaves and sealed them up.

She clambered off the ground, found her own favorite cocoon, and snuggled inside, neatly closing up the big leathery leaves around her. Here she would stay until a better time: a day miraculously cooler and moister than the rest, a time when it might be possible for the Tree to release Ultimate from this protective embrace, to send her out into the world once more — even to seed her belly with another generation of people.

But there would never be another impregnation, never another birth, never another doomed child.

One by one the cocoons would shrivel as their inhabitants, sealed in green, were absorbed back into the bulk of the borametz — and in the end the borametz itself, of course, would succumb, thousands of years old, tough and defiant to the last. The shining molecular chain that had stretched from Purga through generations of creatures that had climbed and leapt, and learned to walk, trod the dirt of another world, and grown small again, and mindless, and returned to the trees — at last that great chain was broken, as the last of Purga’s granddaughters faced an emergency she could not withstand.

Ultimate was the last mother of all. She couldn’t even save her own child. But she was at peace.

She stroked the belly-root and helped it worm its way into her gut. The Tree’s anesthetic and healing chemicals soothed her aching body, closed her small wounds. And as psychotropic vegetable medications washed away the sharp, jagged memory of her lost baby, she was filled with a green bliss that felt as if it would last forever.

It wasn’t such a bad way for the long story to end.

There had been a sighting of another band of feral kids, this time on Bartolome Island. So Joan and Lucy had loaded up the nets and tasers and hypo rifles, and here they were limping over the Pacific in their sun-powered launch.

The flat equatorial sunlight reflected off the water onto Joan’s pocked skin. She was fifty-two now but looked a good deal older, such was the damage that had been done to her skin, not to mention her hair, by the environment she had endured since Rabaul. But Lucy had met very few truly old people in the course of her short life, and she had few points of comparison; to her, Joan was just Joan, her mother, her closest companion.

The day was bright, the few clouds high and streaky. The sun beat hard on the big solar cell sail spread over Lucy’s head. Still, they had packed their heavy-duty ponchos, and every few minutes the women glanced at the sky, fearful of rain that might wash down more of the high dust onto them, the toxic, sometimes radioactive grit that had once been fields and cities and people that was now wrapped around the planet like a thin gray blanket.

And, as always, Joan Useb talked, and talked.

“I always had a soft spot for the British, you know, God rest them. In their heyday they didn’t always behave well, of course. But the human story of the Galapagos was otherwise pretty unhappy: mad Norwegian farmers, Ecuadorian prison camps, everybody eating the wildlife as fast as they could. Even the Americans used the islands as bombing ranges. But all the Brits did to the Galapagos was send over Darwin for five weeks, and all they took away was the theory of evolution.”

Lucy let Joan’s chatter wash through her head, these random echoes from a world she had never known.

Frigate birds wheeled overhead, pursuing the launch as they had pursued the fishing vessels and tourist boats that had once plied these waters. They were great gaunt black-feathered birds that always reminded Lucy of nothing so much as the pterosaurs of her mother’s books and fading printouts. In the water she thought she saw a sea lion, perhaps attracted by the buzz of the launch’s electric motor. But these cute mammals were rare now, poisoned by the toxic garbage that still circulated through the sluggish oceans.

The Galapagos were a bunch of volcanic cones that had been thrust a few million years ago above the surface of the Pacific, here on the equator, a thousand kilometers west of South America. Some of them were little more than a jumble of volcanic boulders, piled up one on top of the other. But others had undergone their own geological evolution. On Bartolome, for instance, the softer outer shells of the older cones had worn away, and the stubborn plugs within had turned crimson red as the iron they contained had rusted. But newer lava had flooded around these older formations, fields of lava bombs, tubes, cones, like a gray-black lunar sea washing around the feet of the stubborn old monuments.

But there was life, here on these new, half-formed islands: Of course there was, a scrap of life that had once been the most famous in the world.

She saw a bird standing gaunt on a small promontory. It was a flightless cormorant: scruffy and black, a thing of stubby useless wings and oily feathers. Standing alone on its bit of volcanic rock, it peered out to sea — patient and still, like so much of the wildlife in this predator-free place, as if waiting for something.

“Ugly, ugly,” Joan murmured. “These islands, the birds and animals. Wonderful, of course, but ugly. Islands have always been great laboratories of evolution. The isolation. The emptiness, populated by a handful of species who raft or fly in, and then radiate into all the empty niches. Like that cormorant. That’s how far you get in three million years, apparently: halfway between a pelican and a penguin. Give it another few megayears, though, and those useless wings will have become genuine flippers, the feathers properly waterproof, and I wonder what they will become then? No wonder Darwin’s eyes were opened here. You can see selection working.”