Semper Human. Ian Douglas

baggage forward in their advance to sapience—notably a hard-wired survival trait that led them, in rather overenthusiastically Darwinian fashion, to utterly obliterate any other species that might constitute a threat. The Xul, it turned out, had been the answer to the age-old question known as the Fermi Paradox. In a Galaxy ten to twelve billion years old, which, given the number of planets and the sheer tenacity and inventiveness of life, should be teeming with intelligent species, the sky was curiously empty. When Humankind had first ventured into its own Solar backyard, then on to the worlds of other nearby suns, it had encountered numerous relics indicating that various species had passed that way before—the Cydonian Face on Mars, the Tsiolkovsky Complex on Luna, the planetwide ruins of Chiron. …

      Eventually, other species had been encountered, and communications begun: the An of Llalande 21185, low-tech remnants of an earlier, vanished stellar empire; the amphibious N’mah, living a precarious rats-in-the-walls existence inside the Sirius Stargate, again the survivors of a once far-flung network of interstellar traders; the Eulers, benthic life forms from the ocean deeps of a world twelve hundred light years from Sol, with a curiously mathematical outlook on Reality and the technology to detonate stars.

      All three species had encountered the Xul scourge, and all three had survived, albeit barely. The Eulers had fought the Xul more or less to a standstill by exploding many of their own stars—creating funereal pyres visible as anomalous novae in Earth’s night skies in the constellation of Aquila, back in the early years of the twentieth century. The N’mah had gone into hiding, deliberately abandoning interstellar travel in favor of survival. The An colony on a gas giant moon had simply been overlooked, and without radio or other attention-getting technologies, had managed to stay overlooked for the next ten to twelve thousand years.

      The Xul, it turned out, had possessed a singular blind spot. Though no longer corporeal, existing as arguably self-aware software within huge and complex computer networks, they’d obviously begun as biological life forms—quite possibly as a number of them—arising on worlds that must have been similar in most respects to Earth in terms of temperature range, gravity, and atmospheric composition. Their blind spot was an inability to see outside of the ecological box; they tended to overlook other possible environments that might harbor life. The current An homeworld, for instance, was an Earth-sized moon of a gas giant, heated from within by tidal flexing, but far outside the so-called habitable zone of the system’s cool, red-dwarf star. The N’mah lived inside entirely artificial but necessary structures, the ten- or twenty-kilometer-wide stargates constructed by a far older, long-vanished congeries of star-faring species. And the Eulers, six-eyed tentacled chemovores evolving near deep-ocean volcanic vents, lived under such crushing pressures that they might have remained forever unnoticed by the Xul hunterships if they hadn’t possessed minds brilliant enough, and curious enough, to develop—through artificially crafted intelligent life forms and a patience spanning perhaps millions of years—the technology to venture into interstellar space.

      All of that had been well known and understood by the time Garroway had joined the Marine Corps, in the twenty-eighth century. During the next few hundred years of his Marine career, perhaps half a dozen other intelligent species had been discovered—the Vorat, the widely scattered Nathga, the Chthuli. Again, nonterrestrial habitats had kept them hidden from the Xul. The Vorat were thermic chemovores, dwelling on high-temperature, high-pressure worlds similar to Venus in Earth’s solar system. The Nathga were jelly-bag floaters that had evolved in the upper cloud levels of a world like Jupiter, eventually developing the technology that had allowed them to slowly migrate to some thousands of similar gas giants across a good third of the Galaxy. And the Chthuli, like the Eulers, were a benthic species that had colonized the ocean basins of several oceanic worlds.

      But across the Galaxy, world after world showed the silent ruins marking the passing of sentient species akin to Humans, in terms of environmental preference and carbon chemistry if not outward form, all blasted into premature extinction by the xenophobic Xul.

      Now, however, some twelve hundred years after the final defeat of the Xul at the Galactic Core, hundreds of nonhuman species had been discovered and contacted to one degree or another. Many had joined the original Terran Commonwealth in a kind of Galactic United Nations—the Associative.

      Many of the more recently discovered species, however, were so alien that they shared little common ground with humans. Communications were difficult, even impossible, with species that communicated by smell or by changing patterns on their integuments or through subtle modulations of their bodies’ electrical fields, with beings that didn’t understand the concept of union, or with entities that thought so slowly they didn’t even appear to be aware of more ephemeral species flitting in and out about them.

      Garroway’s curiosity was piqued as new memories surfaced of strange cultures and alien biologies. He tried querying the data base, hoping to get imagery of some of these beings … then realized his curiosity would have to wait until his implant had grown in fully. He didn’t have that capability yet.

      His military training noticed one important difference between the Associative and the old Commonwealth. There no longer was such a thing as “human space” … or borders between stellar nations. While there were interstellar empires out there, few individual species competed for the same type of real estate, and the “territories” of dozens of different species overlapped. It had been centuries before the Nathga were discovered adrift within the atmospheres of gas giants inside star systems already colonized by humans. The concept of distinct borders had been lost over half a millennium ago.

      How, Garroway wondered, did governments control their own volumes of space? Did they even try … and what changes did that mean for military strategy? For that matter, if there was little or no competition between governments, why was there a need for the military at all?

      And why was there still such a thing as the Marine Corps?

      Surprisingly, he found himself little impressed with the purely technological advances of the past eight hundred years. Most of what he was seeing as new memories continued to surface were further developments of old themes. Interstellar travel still required a mix of the Alcubierre Drive and the huge stargates left behind by a vanished, Galaxy-spanning culture. Quantum power taps, much smaller than the ones Garroway had known, still provided the vast quantities of energy necessary for FTL travel. Nanotechnology had continued its inexorable advance toward the ever-smaller, ever-smarter. Perhaps the most notable technological advances had come in the fields of health and medicine. Some of what he was seeing now he didn’t begin to understand. What the hell was mindkeeping, anyway? Or upload therapy? …

      The Xul threat, he noted, had not entirely vanished after the climactic battle at the Galaxy’s core two decades before he’d been born. Xul nodes—local networks and fleet centers where they’d kept watch over the Galaxy for developing technic cultures—continued to be discovered from time to time, and had to be eliminated one by one. However, thanks to data retrieved from the Galactic center, Xul codes, software, and upload technology all were now well-enough understood that the ongoing mop-up had been turned over to AI assault units. Unmanned probes mimicking Xul hunterships would approach a target system and infect the local node with nanotech devices allowing the assault unit to literally reprogram the local Xul reality. When incoming data suggested that there was a threat that needed to be eliminated, the Xul virtual reality was simply rewritten on the fly to prove that the threat had already been eliminated.

      And so far, the technique appeared to be working. There’d been no new Xul incursions in eight hundred years, and hundreds of Xul bases had subsequently been infiltrated and shut down from within. No new Xul nodes had been discovered in over two centuries, and most people thought that the last of the monsters had been found and destroyed.

      Garroway knew better than to get too excited about that. The Galaxy was an extraordinarily huge place, and more Xul nodes could be—almost certainly were—still out there, lost somewhere within that vastness of four hundred billion suns.

      How’s it going, General? Schillng’s voice said, overriding the torrent of memories.

      Okay, I guess, he replied. Damn, there’s a hell of a lot. …

      He