When we were discussing yesterday the possibility that Epicurus held that there might not be only an infinite number of worlds, but an infinite number of people like us, I could not remember the citation to the proposition that never creates only a single thing of a kind. Here's that reference now,
QuoteIf there is so great a store of seeds as the whole life of living things could not number, and if the same force and nature abides which could throw together the seeds of things, each into their place in like manner as they are thrown together here, you must confess that there are other worlds in other regions, and diverse races of men and tribes of wild beasts. In the universe there is nothing single, nothing born unique and growing unique and alone, but it is always of some tribe, and there are many things in the same race. First of all turn your mind to living creatures; you will find that in this direction is begotten the race of wild beasts that haunts the mountains, in this direction the stock of men, in this direction again the dumb herds of scaly fishes, and all the bodies of flying fowls. Wherefore you must confess in the same way that sky and earth and sun, moon, sea, and all else that exists, are not unique, but rather numberless; inasmuch as the deep-fixed boundary-stone of life awaits these as surely, and they are just as much of a body that has birth, as every race which is here on earth, abounding in things after its kind.
- Lucretius, Book 2:1077