Evolution

Sharing was as old as life itself. Even the cells of Ultimate’s body were the result of mergers of more primitive forms. The most ancient bacteria had been simple creatures, living off the sulfur and heat of hellish early Earth. For them the emergence of cyanobacteria — the first photosynthesizers, which used sunlight to turn carbon dioxide into carbohydrates and oxygen — was a disaster, for reactive oxygen was a lethal poison.

The survivors won by cooperating. A sulfur eater merged with another primitive form, a free-living swimmer. Later an oxygen-breathing bacterium was incorporated into the mix. The three-part entity — swimmer, sulfur-lover, oxygen breather — became capable of reproduction by cell division and could engulf food particles. In a fourth absorption some of the growing complexes engulfed bright green photosynthetic bacteria. The result was swimming green algae, the ancestors of all plant cells. And so on.

Throughout the evolution of life there had been more sharing, even of genetic material. Human beings themselves — and their descendants, including Ultimate — were like colonies of cooperative beings, from the helpful bacteria in their guts which processed foods, to the mitochondria absorbed eons ago that powered their very cells.

So it was now. Joan Useb’s intuition, long ago, had been right: One way or another, the future for mankind had been cooperation, with one another and the creatures around them. But she could never have foreseen this, the final expression of that cooperation.

The Tree, a remote descendant of the borametz of Remembrance’s time, had taken the principle of cooperation and sharing to its extremes. Now the Tree could not survive without the termites and other insects that brought nutrients to its deep roots, and the furry, bright-eyed mammals who brought it water, food, and salt, and planted its seeds. Even its leaves, strictly speaking, belonged to another plant that lived on its surface and fed on its sap.

But likewise the symbiotes, including the posthumans, could not have survived without the succor of the Tree. Its tough leaves sheltered them from predators, from the harsh heat of the climate, even from the once-in-a-century rainstorms. Sap was delivered through the belly-roots, just as the Tree took back its nutrients by the same conduits: infants were not breast-fed but were swaddled by the Tree, nurtured by these vegetable umbilicals. The sap, drawing on the deepest groundwater, sustained them through the mightiest supercontinental droughts — and, laden with beneficent chemicals, the sap healed their injuries and illnesses.

The Tree was even involved in human reproduction.

There was still sex — but only homosexual sex, for there was only one gender now. Sex served only for social bonding, pleasure, comfort. People didn’t need sex for breeding anymore, not even for the mixing of genetic material. The Tree did it all. It took body fluid from one "parent" in its sap and, circulating it through its mighty bulk, mixed it and delivered it to another.

People still gave birth, though. Ultimate herself had given birth to the infant that now lay in its leafy cradle. That heritage, the bond between mother and child, had proved too central to give up. But you no longer fed your child, by breast or otherwise. All you had to give your child was attention, and love. You no longer raised it. The Tree did all that, with the organic mechanisms in its leafy cocoons.

Of course there was still selection, of a sort. Only those individuals who worked well with the Tree and with each other were enfolded and allowed to contribute to the circulating stream of germ material. The ill, the weak, the deformed, were expelled with vegetable pitilessness.

Such a close convergence of the biologies of plant and animal might have seemed unlikely. But given enough time, adaptation and selection could turn a wheezing, four-finned lungfish into a dinosaur, or a human or a horse or an elephant or a bat — and even back into a whale, a fishlike creature, once again. By comparison hooking up people and trees with an umbilical connection was a trivial piece of re-engineering.

In the myths of vanished humanity there had been a kind of foreshadowing of this new arrangement. The Middle Ages’ legends of the Lamb of Tartary had spoken of the Borametz, a tree whose fruit was supposed to contain tiny lambs. All of mankind’s legends were forgotten now, but the tale of the Borametz, with its twining of animal and plant, found strange echoes in these latter days.

But there were costs, as always. Their complex symbiosis with the Tree had imposed a kind of stasis on the postpeople. Over time the bodies of Ultimate and her kind had specialized for the heat and aridity, and had simplified and become more efficient. Once the crucial linking was made, Tree and people became so well adapted to each other that it was no longer possible for either of them to change quickly.