It had taken until the fourth decade of the twenty-first century for humanity to get its act together and learn to resolve or live with its differences, and begin the migration outward as one species toward the stars. In the process, many of the prejudices and irrationalities that had underlain the strife of ages at last withered or were swept away. The core of beliefs that survived would form a solid foundation for the continuing expansion of human knowledge-for surely with the wealth of modern observational data and the sophistication of experimental method, the universe had little left to offer in the way of further reserves of facts to seriously challenge them.

Or so, for a short, comforting while, it seemed.

And then a series of unforeseen and utterly unprecedented events not only added a new dimension to the history of the Solar System, but forced a complete rewriting of the origins of humankind itself.

When Man, under the thrust of the revitalized, international space program that arose from redirection of defense industries after the fading of the Soviet empire, finally reached the regions of the outer planets, he discovered that others had been there before him and had surpassed all that he had achieved. Twenty-five million years in the past, a civilization of eight-foot-tall, benevolently disposed giants-called the Ganymeans, after the first traces of them came to light on Ganymede, largest of the Jovian moons-had flourished on a planet Minerva, occupying the position between Mars and Jupiter.

And more astonishing still, while generations of work by anthropologists, geneticists, comparative anatomists, and others had correctly reconstructed the abrupt transformation responsible for the emergence of Homo sapiens from an arena of early-hominid contenders, it turned out that-understandably, in the circumstances- they had assigned the event to the wrong place. Modern Man hadn’t evolved on Earth at all!

Despite Minerva’s greater distance from the Sun, an effective natural greenhouse mechanism had maintained generally cool but Earth-like conditions there. But by the time the Ganymean civilization reached its advanced stage, the climate was altering in a direction that their constitution would have been unable to tolerate. As was to be expected, their own voyages of discovery across the early Solar System brought them to Earth, and from there they transported back to Minerva numerous plant and animal forms representative of life on late-Oligocene, early-Miocene Earth in connection with large-scale bioengineering researches aimed at combating the problem. These efforts were in vain, however, and the Ganymeans migrated to what later came to be called the Giants’ Star, some twenty light-years from Earth in the direction of the constellation of Taurus.

In the millions of years that followed, the imported terrestrial animals eclipsed and replaced the native Minervan forms, which, owing to a peculiarity of early Minervan biology that had precluded the emergence of land-dwelling carnivores, had evolved no prey-predator adaptations and were unable to compete. These terrestrial types included a population of genetically modified primates as advanced as anything that existed on Earth at the time. Almost twenty-five million years later, fifty thousand years before the present, while the various hominid lines that had been developing on Earth were just yielding the first crude beginnings of stone-using cultures, a second advanced, spacegoing race had already developed on Minerva: the first version of modern Man, subsequently given the name Lunarians when the first evidence of their existence was found in the course of early twenty-first-century exploration of Earth’s moon.

At the time of the Lunarians’ emergence, the Solar System was entering the most recent ice age. Conditions on Minerva were deteriorating, and the Lunarian sciences and industrial technologies developed rapidly as part of a long-term stratagem to move their civilization to the warmer and more hospitable world of Earth.

But such was not to be.

When the Lunarians were practically within reach of the goal toward which they had been working constructively for generations, they embarked on a course of ruinous military rivalries that culminated in a cataclysmic war between two superpowers, Cerios and Lambia, in the course of which the planet Minerva was destroyed.

The Ganymeans by that time had established a thriving interstellar civilization centered on the planet Thurien of the Giants’ Star system. They had never felt comfortable with what they regarded as their abandonment of a genetic mutant that they expected would have no chance of survival, and they had followed the progress of the Lunarians with a mixture of increasing guilt and awe. But when they saw it all end in catastrophe, the Ganymeans forgot their previous policy of nonintervention and appeared in time to save the last few survivors from the war. Gravitational upheavals caused by the emergency methods used to transport the Ganymean rescue mission threw what remained of Minerva into an eccentric outer orbit to become Pluto, while the smaller debris dispersed under Jupiter’s tidal effects as the Asteroids. Minerva’s orphaned moon fell inward toward the Sun and was later captured by Earth.

Despite their experience, the surviving Lunarians remained hostile and immiscible. The Lambians went back with the Ganymeans and were installed on a world called Jevlen, eventually to become a fully integrated, human component of the Thurien civilization. The Cerians were returned, at their own request, to the world of their origins:

Earth, where they were almost overwhelmed shortly afterward by climatic and tidal upheavals caused by the arrival of Minerva’s moon. For thousands of years they reverted to barbarism, struggling on the edge of extinction, and the knowledge of their origins was lost. Only in modern times, when they at last climbed outward once more toward the stars and found the traces of what had gone before, were they able to piece the story together.

The Jevlenese never ceased regarding the people of Earth as Cerians. As part of a plan for one day settling the score with their ancient rivals, they inaugurated a campaign to retard Earth’s progress toward rediscovery of the sciences and advanced civilization, while they themselves absorbed Thurien technology and gained autonomy over their own affairs. From its beginnings, they altered the course of Earth’s history by infiltrating agents, fully human in form, to spread beliefs in magic and superstition, and to found irrational mass movements that would keep Earth impotent by diverting its energies away from the path by which real knowledge is acquired.

As the confidence and arrogance of the Jevlenese leaders grew, so did their resentment of the restraint to their ambitions posed by the Ganymeans, whose nonviolent ways merely aroused their contempt.

Taking advantage of the innate Ganymean inability to suspect motives, the Jevlenese gained control of the surveillance operation set up to keep a watch over Earth’s development; while preserving outward appearances of being model protégés of the Ganymeans, they fed the Ganymeans falsified accounts of a militarized Earth about to burst out from the Solar System, and used this as a pretext for inducing the Ganymeans to prepare countermeasures. What the Jevlenese planned to do was seize control of the countermeasures themselves, eliminate their Terran rivals and repossess the Solar System, and then sweep outward in a wave of acquisition and conquest across the galaxy, unchecked and unopposed.