Eikas cheers to everyone! We recently published On Pleasure as the Default State of the Organism, which defends Epicurean arguments against Cyrenaic conceptions of pleasure. A new SoFE blog has been created on Substack. I am trying a new platform (this will likely replace our mailchimp bulletin) and will slowly diminish my involvement in the bird platform, since I have difficulty trusting their algorithm. Substack allows for subscription, and subscribers receive an email whenever I post a blog. Feel free to subscribe and share.

Now, grant me your attention: hear the truth. A new idea is pressing to be heard, a new aspect of nature to be revealed. But there’s no thought so simple that at first it won’t be difficult to accept, and none so vast, so wonderful, that bit by bit it won’t seem less astounding to us all.

– Lucretius, introducing his explanation of the Doctrine of Innumerable Worlds in De rerum natura, Book 2, 1023-1029

In this essay, I will discuss how modern studies on convergent evolution add flesh, and new dimensions, to the Epicurean theory known as the “Doctrine of Innumerable Worlds“. Before we look at these intersections, let’s first consider what the Doctrine actually says. The earliest attestation of this Doctrine is found in seven statements from tmima (portion) 45 (in the Laertian source) of Epicurus’ Epistle to Herodotus.

1. But, again, the worlds also are infinite,
2. whether they resemble this one of ours or whether they are different from it.
3. For, as the atoms are, as to their number, infinite, as I have proved above, they necessarily move about at immense distances;
4. for besides the infinite multitude of atoms, of which the world is formed, or by which it is produced, could not be entirely absorbed by one single world,
5. nor even by any worlds, the number of which was limited,
6. whether we suppose them like this word of ours, or different form it.
7. There is therefore, no fact inconsistent with an infinity of worlds.

To help us evaluate the Doctrine, I broke it down into seven statements: that (1) the worlds are innumerable; that (2) some are similar and some are different from our own; that (3) since atoms are innumerable and must cover great distances (an idea that is discussed elsewhere), (4) therefore these atoms can not be contained within a single world, (5) or even within any limited number of worlds (6) which may, again, be similar to or different from our own. This point is stressed twice, which adds emphasis on the diversity of worlds. It closes (7) with a conclusive declaration based on all the facts noted.

Notice the stress on how worlds may be similar to, or different from, our own world. Exoplanetary research sheds more light, and adds specificity, to this. When we read the word “world”, in the original, the word kosmos is used. This is why many interpret this as a theory about a multiverse.

Two centuries later, when Lucretius in Liber Secvndvs of De Rerum Natura continues to expound the same doctrine, his final concluding statement is:

One must grant there are other earthly spheres
in other regions, with different races
of human beings and classes of wild beasts.

But how does this tie into convergent evolution? Convergent evolution documents certain traits that have been observed to evolve, in separate lineages, multiple times, so that this is seen as evidence that these traits are highly useful. This video titled “Why do things keep evolving into crabs?” sheds light on this fascinating aspect of the theory of evolution by natural selection.

The intersection between this and the Doctrine of the Innumerable Worlds lies in astrobiology: the more examples of convergent evolution we see in different Earth environments, the more likely we are to find similar traits in living beings in the innumerable worlds. Until we are able to acquire direct evidence, this is currently a matter of mathematics. This line of reasoning adds flesh to the Doctrine of Innumerable Worlds. Using our method of inference by analogy, when we find planets that are similar enough to our own, we can infer that Earth-like life probably exists there, or that it may evolve if some conditions change; and according to convergent evolution studies, specific evolutionary pressures will likely strongly favor certain traits that we are already familiar with.

Examples of convergence can be found in the shapes of the bodies of certain creatures. The shape of a snake evolved both in the water (as eels) and on land. Eight-legged creatures evolved separately multiple times, probably because symmetry is useful. These lineages include varieties of crabs, spiders and other creatures. Flight evolved separately in insects, avians, and some mammals. The behavior and calls of social animals who hunt together also converges: the calls of dolphins and the howls of wolves have been observed to share striking similarities. Ants evolved separately from termites, yet they both have caste systems.

What kinds of creatures might be flying or howling together somewhere in the innumerable worlds?

If Lucretius’ explanation of this Doctrine is true, truth may be stranger than fiction, because he was extremely optimistic about the prospects of extraterrestrial life. Lucretius specifically mentions that different species of human-like beings would be found in space. This would mean that humanity is a convergent trait. Is it?

We know that, on Earth, human lineages evolved multiple times–as Denisovan, Neanderthal, Luzonian and Flores hobbits, Homo Longi in China, our Cro-Magnon ancestors, and several other ancestral hominid species in Africa and Papua that we know very little about. This seems to suggest that the traits that generally make up a human or hominid are convergent. However, only our lineage survived, which raises the possibility that the rise of a species like ours may bring about the destruction or displacement of many other species, and that nature pays a high price for producing certain types of highly-intelligent and adaptable sentient beings in terms of sacrificing the diversity of ecosystems.

Whether or not humanity might be an example of convergent evolution, Lucretius (and, presumably, other early atomists) seemed convinced that it was something like it, and declared plainly that there were other hominids in the innumerable worlds. So we can imagine a human-like model of sentient being that lives by its wit–rather than by fangs, horns or venom–and eventually develops forms of culture, civilization and technology that we may recognize as familiar. The bodily shape of this creature would be somewhat similar to ours. Eagles are smart, but they do not have the manual dexterity to construct complex machines: body shape matters.

Our brains evolved to be much larger and different from other great ape brains over a relatively short period of time, and we don’t fully understand how this came to be. The answer to this may help us to predict how likely we are to find higher intelligences elsewhere.

To conclude, the fields of study that inform convergent evolution add flesh to the ancient astrobiology theories that we find in Epicurus’ Letter to Herodotus and Lucretius’ De rerum natura (and which later inspired the comical speculations about alien life we find in Lucian’s True History, believed to be the very first work of science fiction ever written). They also hint at how potentially advanced their speculation about alien life-forms was–even without the benefit of modern scientific methods and theories–, and how natural cosmology is just as rich and awe-inspiring as the supernatural theories that seek to replace it.