Just for sake of the record (not to derail my own thread), let me also mention that near the end of Karl Kautsky’s 1927 massive two-volume magnum opus Die Materialistische Geschichtsauffassung [The materialist conception of history] (1927), in a section titled ‘Astronomical conception of history’, he discusses the issue of extraterrestrial life that has similar-to-human intelligence (see pp. 763–69 in volume two, or in the 1988 abridged English translation pp. 505–6). I give here a quick e-translation of Kautsky’s passage in full.

It’s quite superficial (so feel free to ignore it). It is sort of a tangent/riff on a remark in a 1922 work by the protestant theologian Ernst Troeltsch.

[Kautsky quotes a long passage from Troeltsch, Der Historismus, pp. 85-87, who insists that there must be in the universe a multiplicity of “realms of life” or “realms of the spirits’ —evidently manlike spirits—each with its own history.]

Troeltsch is absolutely right. It would be absurd to assume that the functions of life and spirit are to be found only on our Earth. Perhaps around each of the fixed stars, certainly around many of them, orbits a network of "no longer glowing, dark planets," quite a few of which will exhibit similar conditions to Earth and therefore similar structures, living beings endowed with spiritual abilities. However, why this assumption should make the imperfection of our existence "at all" bearable is not entirely clear. But the assumption itself has the greatest probability in its favor.

But that is not enough for the purposes Troeltsch pursues. To achieve them, he must simply transform the "realm of life" into a "realm of spirits," namely a realm of human spirits. For only these make history—in the way we have seen it, through the continuous creation of artificial organs that become a new environment for humans.

If "human history and the human spirit" are to cease to be "a terrifying anomaly in the world," then we must be shown the greatest probability that human history and the human spirit also exist in the numerous other life realms that we have every reason to assume.

But it is not only possible to make this probability plausible. In fact, we have every reason to assume the opposite.

Even if we compare humans only with the "life realm" of Earth, "the quantitative disproportion remains shocking." Consider the short span of humanity's existence compared to the hundreds of millions of years of the organic world's existence on our planet.

But is it easy to assume that there is currently another planet in the universe that offers living beings exactly the same conditions of existence at exactly the same level of development as Earth? One that is as large as it, whose atmosphere has the same chemical composition, whose mass exerts the same attraction on the bodies on its surface, whose orbital velocity around the sun is the same, as is its rotational speed on its axis, whose axis is the same relative to the ecliptic, whose distance from the sun, and whose sun is as bright and as hot as ours?

All these conditions of existence must be comparable to those on present-day Earth, if organisms of the same kind as those on Earth are to exist on that other planet. And many other conditions of existence must be the same here as there if humans are to be possible outside of Earth.

All of the conditions of existence just listed were already the same on Earth as they are today, before humans even appeared. Special environmental conditions had to arise to make a particular type of living being into humans.

We may well assume that in the infinite universe there is an infinite number of planets that make organic life possible and support it. But we must also assume that the number of variations in the conditions of existence that can occur on these planets is also infinite. So that hardly any of them will ever repeat the forms of the other. And the more diverse these forms are, the less likely they will be.

The simplest, most primitive forms, the primordial beings, may be the same on different planets. The higher the forms*, however, the greater the improbability that they will be found elsewhere. This is the greatest danger for humans. One can consider it virtually impossible that there are humans on any other celestial body. "Sober astronomers" may search for Martians, but it is complete folly to look for Martians [Mars-people], given that the conditions of existence on Mars are so different from the earthly conditions. This folly reaches its peak when astronomers assume that there are humans on Mars who are at the same level of culture as we are, so that one could communicate with them.

If one states that no two leaves of a tree are exactly alike, one must assume the same for the celestial bodies and thus also for the organisms that shelter those stars whose stage of development makes them suitable for organic life.

If the human race is a singular and extremely tiny phenomenon in the world, so too is its spirit and its history, despite all the talk of the "world spirit" which is only "the masters' own spirit."

Troeltech believes, that the various spiritual beings of the various planets "presumably stand at very different levels of perfection according to their conditions of existence and all have their own history."

The beginning of the sentence must be accepted. This does not mean that it is entirely correct. One must not forget that what we call history is a special kind of development which is connected with special abilities that enable the mammal to create artificial organs.

Organisms that have not attained these capacities have no history, although they exhibit development. Not even gorillas and chimpanzees, although at a relatively high level of intellectual ability, have a history.

On the other hand, it is by no means certain that creatures more intelligent than humans must have a history. They may live in such blissful conditions that they do not desire or strive for their change. How can history arise in this situation?

Although we reject the view that the object of history is the only, singular thing, we must nevertheless hold the view that human history itself is something unique in the universe, which cannot easily be equaled.

However, it becomes a "terrifying anomaly" if one assumes that it, like the human mind, stands outside the causal context of the world and that it has its own special movement in itself and through itself, and that it has a special purpose and special meaning, even if such a purpose cannot be found elsewhere in the world.

The path Troeltsch seeks in order to save the special position of human history and the human mind in the universe is strange enough. It is even surpassed by the one taken by [Hans] Delbrück.

In the introduction to his World History [1923], he asks:

Why do we study history at all? Is it worth the effort to study it? Does it have a rational meaning?

p. 2

He must admit that it seems absurd to ask for a rational meaning of existence on Earth for the world, in which our planet is merely a tiny dot.

One could only search for a meaning of the world and history if one assumed that humanity was the center of the world. But isn't that a ridiculous idea?

Should all these infinite worlds have no other purpose than to sublime the inhabitants of this one star? As Kant could say: the starry sky above us and the infinite moral law within us? ... Both science and religion are collapsing in the face of this incongruity.

But it is precisely in this naturalistic perspective that Delbruck finds a saving grace for his conception of history. "As they (the natural sciences – Kautsky) have covered the infinite universe of which one side is infinite vastness and, the other, infinite smallness."

Here it measures the distances of stars in 1000 years, there the size of electrons in a 10 billionth of a centimeter. This advance in natural science changes things colossally.

[long quote from Delbruck:]

Man has returned to the center, for the infinitely large is just as distant to him on the one hand as the infinitely small on the other. He stands at the dividing point between macroscopic and microscopic endlessness. The more closely visible scales themselves disappear with the reality of space, and the human spirit, which partakes of the infinite, the divine spirit, rises above all nature and above all nature. The spirit is the center and essence of the world, true being, and all the vastness of the stars, just as all the mysteries of nature have to serve him and serve him.

Should spirit also exist outside of humanity? It is excluded from the outset in the glowing gas of the sun and all the fixed stars, and if one were to imagine that among the planets there were one or another that might possibly offer the conditions for it, nothing would be gained: instead of a tiny point in the universe, we would then have a few such dots...

"In order to attain consciousness, the finite spirit, which shares in the infinite*, the divine spirit, requires a highly elaborate body, the limb of man,

Only in man can it attain consciousness of itself, and the earth is the center of the universe* not topographically, but because it is man's abode. It is true, after all, that the most distant suns and stars are only there so that man can say: the starry sky above me and the law within me.

One sees, Delbrück rejects the solution to which Troeltsch takes refuge, the assumption of numerous "spirit realms".

As a spirit, he only seeks the human one, which is unique to the Earth.

But the anomaly does not frighten him that such a tiny dot in the infinite universe should be above its laws, for this dot appears to him all-powerful by virtue of being a middle dot.

Humans reach this grandiose position simply by being as far removed from the infinitely great as from the infinitely small, from which it naturally follows that they form the "center" of the world.

This striking argument has only one small flaw: It does not apply to humans alone. It can be applied to anything. And the elephant is as far removed from the infinitely great as from the infinitely small. The fly is no less so. Indeed, everything ends in the end, no matter how big or small it may be, the sun or a speck of dust.

Delbrück refers to Kant. Well, in his work he could find sentences like the following:

The infinity of creation is large enough to compare a world or a galaxy of worlds with it, as one compares a flower or an insect with the Earth

General Nature, Principles and Theory of the Heavens, £755, edited by Dr. Otto Bude, Leipzig, 1909, p. 129, Part 11, Capital.

"Everything that is finite, that has its own tendencies and a definite relationship to unity, is equidistant from the infinite" (loc. cit., p. 11).

Thus we come to the conclusion that every thing stands at the center of the world, not just man. Or, and this would be more accurate: Nothing stands at the center of the universe, because there can be no center for the infinite. Only a finite space can have a center.

For Delbrück, it is not enough to discover that man is both infinitely large and infinitely large. Equally distant from the small. Here, one must imagine the human body with a certain extension. Immediately afterwards, however, Delbrück replaces the human body with the human spirit, which has no extension at all because it is not a thing but a collection of functions, making it the center of the universe. The spatial center then immediately becomes a spiritual dominion over the world, which must serve the center. What breakneck leaps!

But what was at the center of the universe in the aeolians before the emergence of man? Who did it serve back then?

It takes a great deal of religion to venture such bold conclusions as Delbrück does. However, how else can one prove the authenticity of the transition to the course of history, freed from the causal necessity of the world?

Anyone who is so firmly convinced of the divine nature of the human spirit and the history in which it manifests itself (or "interprets" itself, to use Hegel's term) will find transcendent historical prognostications easy.

Such prognostications, however, are also produced by less religious researchers, even among socialists.

Not only for the coming centuries, but for all time, they prophesy the unstoppable rise of the human race.

Like the flower, humanity is naturally implanted with the urge to grow toward the light, into brighter spheres of existence.

And they, too, place man at the center of the world. H. G. Wells concludes his "Outline of History" [1920] with the following intoxicating outlook:

Gathered together at last under the leadership of man, the student-teacher of the universe, unified, disciplined, armed with the secret powers of the atom and with knowledge as yet beyond dreaming, Life, for ever dying to be born afresh, for ever young and eager, will presently stand upon this earth as upon a footstool, and stretch out its realm amidst the stars.

It is not yet clear what kind of "life" this is supposed to be that allows humans to lead it, and is therefore different from living humans. A life that uses springboards and builds foundations among the stars. But there is no doubt that this fantasy sounds magnificent and makes us tremble with ecstasies of joy.

It is strange how little the earth suffices these historical philosophers; they always feel the need* to reach beyond it to the "eternal stars."

It seems as if not least highly progressive elements are predisposed to accepting such exuberant views of humanity's position and future, even those who are not at all religious, including highly godless positivists, materialists, and atheists.

Belief in unstoppable, endless progress is naturally most readily found among those who work for it—that is, in the classes produced by industrial capitalism. They are most likely to share the optimism for the future that the rapid development of the productive forces brings with it, despite all the suffering and sacrifice that arise in the present.

But if the belief in progress toward the true, the beautiful, and the good corresponds to the mood that emerges from the modern mode of production, in contrast to the pessimism of the Roman imperial era, why not simply accept Marx's prognosis, which is based on solid facts?

Yes, it is unfortunately based on such an unpleasant and vulgar fact as the class struggle of the proletariat.

Only proletarians and the advocates of their class interests can recognize it. For everyone else, it is inconvenient. For many who are directly interested in capital, but also for some who simply want peace, it is considered a phenomenon that cannot be tolerated.

Our social conditions are, of course, too painful and repulsive for every thinking and feeling person not to turn against them. How much more comfortable and gratifying (for non-proletarians) is, however, the prospect of an inevitable rise of humanity, which necessarily arises from its nature, that is, without strikes and revolutions, expropriations and similar disgusting things, solely through the inner workings of our minds, our conscience, which is becoming ever more delicately strung through the progress of time.

Everyone can believe in such a perfection of humanity, even the most die-hard reactionary of the present.

Even he can see the distant future of humanity in its brightest splendor.

However, the predictions of humanity's steady progress are not exclusively transcendent in nature, nor are they born merely of psychological needs and moods.

In part, they are also conclusions from observed facts. And we have yet to examine the extent to which these conclusions are well-founded. This concludes our presentation of the materialist conception of history.