The human race, it seemed, had gotten smart just in time to save itself. But it had been a difficult adolescence.

Even as the human population had continued to swell, climatic changes had devastated much of the world’s food and water supply, with the desertification of the great grain regions of the U.S. and Asia, the drowning of many productive lowland farming areas by rising sea levels, and the pollution of aquifers and the acidification or drying of freshwater lakes. Soon the problem of excess population went into reverse as drought, disease and starvation culled communities across the planet. It was a crash only in relative terms; most of Earth’s population had survived. But as usual the most vulnerable — the very old and the very young — had paid the price.

Overnight, the world had become middle-aged.

New generations had emerged into a world that was, recovering, still crowded with ageing survivors. And the young — scattered, cherished, WormCam-linked — regarded their elders with increasing intolerance, indifference and mistrust.

In the schools, the children of the WormCam made academic studies of the era in which their parents and grandparents had grown up: an incomprehensible, taboo-ridden pre-WormCam age only a few decades in the past in which liars and cheats had prospered, and crime was out of control, and people killed each other over lies and myths, and in which the world had been systematically trashed through willful carelessness, greed, and an utter lack of sympathy for others or foresight regarding the future.

And meanwhile, to the old, the young were a bunch of incomprehensible savages with a private language and about as much modesty as a tribe of chimpanzees…

But the generational conflict was not the full story. It seemed to Bobby that a more significant rift was opening up.

The mass minds were still, Bobby supposed, in their infancy, and they were far outnumbered by the Unjoined older generations — but already their insights, folded down into the human world, were having a dramatic effect.

The new superminds were beginning to rise to the greatest of challenges: challenges which demanded at once the best of human intellect and the suppression of humanity’s worst divisiveness and selfishness. The modification and control of the world’s climate, for example, was, because of the intrinsically chaotic nature of the global weather systems, a problem that had once seemed intractable. But it was a problem that was now being solved.

The new generations of maturing Joined were already shaping the future. It would be a future in which, many feared, democracy would seem irrelevant, and in which even the consolation of religion would not seem important; for the Joined believed — with some justification — that they could even banish death.

Perhaps it would not even be a human future at all.

It was wonderful, awe-inspiring, terrifying. Bobby knew that he was privileged to be alive at such a moment, for surely such a great explosion of mind would not come again.

But it was also true that he — and David and the rest of their generation, the last of the Unjoined — had come to feel more and more isolated on the planet that had borne them.

He knew this shining future was not for him. And — a year after Kate’s death, the illness that had suddenly taken her from him — the present held no interest. What remained for him, as for David, was the past.

And the past was what he and David had decided to explore, as far and as fast as they could, two old fools who didn’t matter to anybody else anyhow.

He felt a pressure — diffuse, almost intangible, yet summoning. It was as if his hand were being squeezed. “David?”

“Are you ready?”

Bobby let a corner of his mind linger in his remote body, just for a second; shadowy limbs formed around him, and be took a deep breath, squeezed his hands into fists, relaxed again. “Let’s do it.”

Now Bobby’s viewpoint began to fall from the African sky, down toward the southern coast. And as he fell, day and night began to flap across the patient face of the continent, centuries falling away like leaves from an autumn tree.

A hundred thousand years deep, they paused. Bobby and David hovered like two fireflies before a face: heavy-browed, flat-nosed, clear-eyed, female.

Not quite human.

Behind her, a small family group — powerfully built adults, children like baby gorillas — were working at a fire they had built on his ancient beach. Beyond them was a low cliff, and the sky above was a crisp, deep blue; perhaps this was a winter’s day.

The brothers sank deeper.

The details, the family group, the powder-blue sky, winked out of existence. The Neanderthal grandmother herself blurred, becoming expressionless, as one generation was laid over another, too fast for the eye to follow. The landscape became a greyish outline, centuries of weather and seasonal growth passing with each second.

The multiple-ancestor face flowed and changed. Half a million years deep her forehead lowered, her eye socket ridges growing more prominent, her chin receding, her teeth and jaws pronounced. Perhaps this face was now ape-like, Bobby thought. But those eyes remained curious, intelligent.

Now her skin tone changed in great slow washes, dark to light to dark.

“Homo Erectus.” David said. “A toolmaker. Migrated around the planet. We’re still falling. A hundred thousand years every few seconds, good God. But so little changes!…”

The next transition came suddenly. The brow sank lower, the face grew longer — though the brain of this remote grandmother, much smaller than a modern human’s, was nevertheless larger than a chimpanzee’s.

“Homo Habilis,” said David. “Or perhaps this is Australopithecus. The evolutionary lines are tangled. We’re already two million years deep.”

The anthropological labels scarcely mattered. It was profoundly disturbing, Bobby found, to gaze at this flickering multi-generation face, the face of a chimpanzee-like creature he might not have looked at twice in some zoo… and to know that this was his ancestor, the mother of his grandmothers, in an unbroken line of descent. Maybe this was how the Victorians felt when Darwin got back from the Galapagos, he thought.

Now the last vestiges of humanity were being shed, the brain pan shrinking further, those eyes growing cloudy, puzzled.

The background, blurred by the passage of the years, became greener. Perhaps there were forests covering Africa, this deep in time. And still the ancestor diminished, her face, fixed in the glare of the WormCam viewpoint, becoming more elemental, those eyes larger, more timid. Now she reminded Bobby more of a tarsier, or a lemur.

But yet those forward-facing eyes, set in a flat face, still held a poignant memory, or promise.

David impulsively slowed their descent, and brought them fleetingly to a halt some forty million years deep.

The shrew-like face of the ancestor peered out at Bobby, eyes wide and nervous. Behind her was a background of leaves, branches. On a plain beyond, dimly glimpsed through green light, there was a herd of what looked like rhinoceros — but with huge, misshapen heads, each fitted with six horns. The herd moved slowly, massive, tails flicking, browsing on low bushes, and reaching up to the dangling branches of trees. Herbivores, then. A young straggler was being stalked by a group of what looked like horses — but these “horses,” with prominent teeth and tense, watchful motions, appeared to be predators.

David said, “The first great heyday of the mammals. Forests all over the planet; the grasslands have all but disappeared. And so have the modern fauna: there are no fully-evolved horses, rhinos, pigs, cattle, cats, dogs…”