For a million terrestrial years these long-armed hairless beings were spreading their wicker huts and bone implements over the great northern continents, and for many more millions they remained in possession without making further cultural progress; for evolution, both biological and cultural, was indeed slow on Neptune. At last the Tenth Men were attacked by a micro-organism and demolished. From their ruins several primitive human species developed, and remained isolated in remote territories for millions of decades, until at length chance or enterprise brought them into contact. One of these early species, crouched and tusked, was persistently trapped for its ivory by an abler type, till it was exterminated. Another, long of muzzle and large of base, habitually squatted on its haunches like the kangaroo. Shortly after this industrious and social species had discovered the use of the wheel, a more primitive but more war-like type crashed into it like a tidal wave and overwhelmed it. Erect, but literally almost as broad as they were tall, these chunkish and bloody-minded savages spread over the whole arctic and sub-arctic region and spent some millions of years in monotonous reiteration of progress and decline; until at last a slow decay of their germ-plasm almost ended man’s career. But after an aeon of darkness, there appeared another thick-set, but larger brained, species. This, for the first time on Neptune, conceived the religion of love, and all those spiritual cravings and agonies which had flickered in man so often and so vainly upon Earth and Venus. There appeared again feudal empires, militant nations, economic class wars, and, not once but often, a world-state covering the whole northern hemisphere. These men it was that first crossed the equator in artificially cooled electric ships, and explored the huge south. No life of any kind was discovered in the southern hemisphere; for even in that age no living matter could have crossed the roasting tropics without artificial refrigeration. Indeed, it was only because the sun’s temporary revival had already passed its zenith that even man, with all his ingenuity, could endure a long tropical voyage.

Like the First Men and so many other natural human types, these Fourteenth Men were imperfectly human. Like the First Men, they conceived ideals of conduct which their imperfectly organized nervous systems could never attain and seldom approach. Unlike the First Men, they survived with but minor biological changes for three hundred million years. But even so long a period did not enable them to transcend their imperfect spiritual nature. Again and again and again they passed from savagery to world-civilization and back to savagery. They were captive within their own nature, as a bird in a cage. And as a caged bird may fumble with nest-building materials and periodically destroy the fruit of its aimless toil, so these cramped beings destroyed their civilizations.

At length, however, this second phase of Neptunian history, this era of fluctuation, was brought to an end. At the close of the six hundred million years after the first settlement of the planet, unaided nature produced, in the Fifteenth human species, that highest form of natural man which she had produced only once before, in the Second species. And this time no Martians interfered. We must not stay to watch the struggle of this greatheaded man to overcome his one serious handicap, excessive weight of cranium and unwieldy proportions of body. Suffice it that after a long-drawn-out immaturity, including one great mechanized war between the northern and southern hemispheres, the Fifteenth Men outgrew the ailments and fantasies of youth, and consolidated themselves as a single world-community. This civilization was based economically on volcanic power, and spiritually on devotion to the fulfilment of human capacity. It was this species which, for the first time on Neptune, conceived, as an enduring racial purpose, the will to remake human nature upon an ampler scale.

Henceforth in spite of many disasters, such as another period of earthquake and eruption, sudden climatic changes, innumerable plagues and biological aberrations, human progress was relatively steady. It was not by any means swift and sure. There were still to be ages, often longer than the whole career of the First Men, in which the human spirit would rest from its pioneering to consolidate its conquests, or would actually stray into the wilderness. But never again, seemingly, was it to be routed and crushed into mere animality.

In tracing man’s final advance to full humanity we can observe only the broadest features of a whole astronomical era. But in fact it is an era crowded with many thousands of long-lived generations. Myriads of individuals, each one unique, live out their lives in rapt intercourse with one another, contribute their heart’s pulses to the universal music, and presently vanish, giving place to others. All this age-long sequence of private living, which is the actual tissue of humanity’s flesh, I cannot describe. I can only trace, as it were, the disembodied form of its growth.

The Fifteenth Men first set themselves to abolish five great evils, namely, disease, suffocating toil, senility, misunderstanding, and ill-will. The story of their devotion, their many disastrous experiments, and ultimate triumph, cannot here be told. Nor can I recount how they learned and used the secret of deriving power from the annihilation of matter, nor how they invented ether-ships for the exploration of neighbouring planets, nor how, after ages of experiments, they designed and produced a new species, the Sixteenth, to supersede themselves.

The new type was analogous to the ancient Fifth, which had colonized Venus. Artificial rigid atoms had been introduced into its bone-tissues, so that it might support great stature and an ample brain; in which, moreover, an exceptionally fine-grained cellular structure permitted a new complexity of organization. ‘Telepathy’, also, was once more achieved, not by means of the Martian units, which had long ago become extinct, but by the synthesis of new molecular groups of a similar type. Partly through the immense increase of mutual understanding, which resulted from ‘telepathic’ rapport, partly through improved coordination of the nervous system, the ancient evil of selfishness was entirely and finally abolished from the normal human being. Egoistic impulses, whenever they refused to be subordinated, were henceforth classed as symptoms of insanity. The sensory powers of the new species were, of course, greatly improved; and it was even given a pair of eyes in the back of the head. Henceforth man was to have a circular instead of a semi-circular field of vision. And such was the general intelligence of the new race that many problems formerly deemed insoluble were now solved in a single flash of insight.

Of the great practical uses to which the Sixteenth Men put their powers, one only need be mentioned as an example. They gained control of the movement of their planet. Early in their career they were able, with the unlimited energy at their disposal, to direct it into a wider orbit, so that its average climate became more temperate, and snow occasionally covered the polar regions. But as the ages advanced, and the sun became steadily less ferocious, it became necessary to reverse this process and shift the planet gradually nearer to the sun.

When they had possessed their world for nearly fifty million years, the Sixteenth Men, like the Fifth before them, learned to enter into past minds. For them this was a more exciting adventure than for their forerunners, since they were still ignorant of Terrestrial and Venerian history. Like their forerunners, so dismayed were they at the huge volume of eternal misery in the past, that for a while, in spite of their own great blessings and spontaneous gaiety, existence seemed a mockery. But in time they came to regard the past’s misery as a challenge. They told themselves that the past was calling to them for help, and that somehow they must prepare a great ‘crusade to liberate the past’. How this was to be done, they could not conceive; but they were determined to bear in mind this quixotic aim in the great enterprise which had by now become the chief concern of the race, namely the creation of a human type of an altogether higher order.

It had become clear that man had by now advanced in understanding and creativeness as far as was possible to the individual human brain acting in physical isolation. Yet the Sixteenth Men were oppressed by their own impotence. Though in philosophy they had delved further than had ever been possible, yet even at their deepest they found only the shifting sands of mystery. In particular they were haunted by three ancient problems, two of which were purely intellectual, namely the mystery of time and the mystery of mind’s relation to the world. Their third problem was the need somehow to reconcile their confirmed loyalty to life, which they conceived as embattled against death, with their ever-strengthening impulse to rise above the battle and admire it dispassionately.

Age after age the races of the Sixteenth Men blossomed with culture after culture. The movement of thought ranged again and again through all the possible modes of the spirit, ever discovering new significance in ancient themes. Yet throughout this epoch the three great problems remained unsolved, perplexing the individual and vitiating the policy of the race.

Forced thus at length to choose between spiritual stagnation and a perilous leap in the dark, the Sixteenth Men determined to set about devising a type of brain which, by means of the mental fusion of many individuals, might waken into an altogether new mode of consciousness. Thus, it was hoped, man might gain insight into the very heart of existence, whether finally to admire or loathe. And thus the racial purpose, which had been so much confused by philosophical ignorance, might at last become clear.

Of the hundred million years which passed before the Sixteenth Men produced the new human type, I must not pause to tell. They thought they had achieved their hearts’ desire; but in fact the glorious beings which they had produced were tortured by subtle imperfections beyond their makers’ comprehension. Consequently, no sooner had these Seventeenth Men peopled the world and attained full cultural stature, than they also bent all their strength to the production of a new type, essentially like their own, but perfected. Thus after a brief career of a few hundred thousand years, crowded with splendour and agony, the Seventeenth gave place to the Eighteenth, and, as it turns out, the Last, human species. Since all the earlier cultures find their fulfilment in the world of the Last Men, I pass over them to enlarge somewhat upon our modern age.