How could material nature conceivably account for the order and purposes of nature, and, above all, for the adaptation of living entities to their surroundings and to their requirements for survival and procreation? Almost all early-modern learned minds asked that question. “Open your eyes and gaze upon the order of the universe,” work after work of academic and popular theology advised.

René Descartes’s and the Cartesians’ antifinalism did not reject such a view. The eminent Cartesian Bernard Le Bovier de Fontenelle saw the most efficacious proof of God in the mutual dependence of all things upon all others in the infinite number of relationships necessary for survival. For Fontenelle, no hypothesis of chance or gradual development was remotely plausible. All things must have been, from the start, in their current mutually dependent and mutually beneficial condition; otherwise, they could not have survived. Indeed, Descartes himself, in the Discourse, had argued that astute thinkers “will consider the body as a machine, that, having been made by the hands of God, is incomparably better arranged and possesses more admirable movements, than any of those that could be invented by men.”

Anatomy, for most early-modern thinkers, demonstrated in the clearest possible manner the indispensability of infinitely wise intelligent choice to coherent explanation. Denial that ears were made for hearing, eyes for seeing, and sexual organs for reproducing seemed inane, a perverse unwillingness to recognize the clear anatomical evidence of divine providence. Isaac Newton spoke for most of his contemporaries when, in Question 31 of the Optics, he argued that blind chance never could explain the uniformity, the suitedness, and the utility of the parts of animal bodies. Before Charles Darwin, how bizarrely speculative it seemed to think of suitedness as the effect not the cause of natural phenomena. For most, it was analogous to thinking that a clock told time because the mechanism had arranged itself blindly. In the seventeenth century, the Epicurean view that form determined function, not the reverse, seemed so incongruous that it was widely expounded to show the benighted state of the human mind before Christianity.

That Epicurean tradition, however, was deeply known in the early-modern learned world by means of classical, Patristic, Scholastic, and contemporaneous expositions, paraphrases, commentaries, and explications; by commonplace caricature; by frequent pedagogical reference to its significance as a major school of ancient thought. This transmission was for purposes both of erudition and of refutation from Christian perspectives. It was increasingly known, above all, through Lucretius’s De rerum natura, which between 1600 and 1800 had appeared in over eighty European editions, both in Latin (the majority) and in English, French, Italian, Dutch, and German.

Christian theism and its increasingly confident current of physical theology saw the adaptation of all beings to their niche in the world as unanswerable proof of providence and God. The Epicurean reply to such argument provided, for those who otherwise did not see proofs of God as convincing, a naturalistic alternative. As stated in De rerum natura, nature had produced many defective beings that could not propagate because they were not fit for their surroundings. Many kinds of life had perished on earth. The species that survived had lived on because they were suited to sustenance and procreation in their settings. This followed simply from variety and necessity. It was all explicable in natural terms: “For we see that living beings need many things in conjunction, so that they may be able by procreation to forge out the chain of the generations.” As I have tried to show in my larger body of work, orthodox learned Christian culture recounted Lucretius’s narrative and conceptual framework often and in every print medium.

In the wake of countless expositions of Epicureanism and the ubiquity of Lucretius in the learned world, however, Epicurean naturalism became a small but vital current by the late seventeenth century. The most influential late-seventeenth-century neo-Epicurean was Guillaume Lamy, doctor-regent of the Faculty of Medicine of the University of Paris. His De Principiis Rerum (1669) was a critical comparison of the “three world systems,” Aristotelian, Cartesian, and Epicurean, in which the author favored Epicureanism at every turn.

In Lamy’s Discours Anatomiques (1675, reprinted in Brussels in 1679), addressing the nature of anatomy, he argued that purposeful function did not create form, but, rather, form created function. The suitedness of living things was the outcome of chance. To reason from use to purpose was the equivalent of believing that God has created the clitoris so that women could masturbate. Eyes and ears were not made so that we could see and hear; rather, we saw and heard because physiologically we had ears and eyes. The goal of anatomy was to describe according to experience, not to fabricate occult causes beyond its ken.

Matter in motion blindly made this or that part, without purpose. The suitedness of species could be accounted for by the Epicurean system: The diverse arrangements of matter had produced a large variety of animals of different species. Most were not suited for survival or procreation, and, unable to feed themselves, or multiply, they were not observable now by natural philosophers. The remainder, some small minority of the original animals, were well suited to preserve themselves, and they composed the species that we observe today. Only the suited survived and procreated, and the world was populated by animals whose arrangements appeared suited for their needs, which wrongly occasioned our wonderment. Lamy claimed that only faith could see God in all this, where philosophy sought knowledge of a system by which all things had come to be as we observed them without the intervention of intelligence.

The materialist Julien Offray de La Mettrie drank deeply (and explicitly) from Lamy’s well, and the quintessential Enlightenment atheist, the baron d’Holbach, knew Lamy’s work, knew La Mettrie’s use of him, and had a deep and active interest in Lucretius’s De Rerum Natura. The catalog of Holbach’s library revealed that the baron owned twelve Latin, English, Italian, and French editions of De Rerum Natura and all of Guillaume Lamy’s major works. Further, he sponsored Nicolas La Grange’s prose translation of Lucretius (1768), frequently reprinted through the 1820s. La Grange’s work, with his own introduction and critical notes, was produced while La Grange was the private tutor of the wealthy Holbach’s children, and with the scholarly assistance of Holbach and his atheistic friends Denis Diderot and Jacques-André Naigeon.

Jean-Jacques Rousseau’s Confessions described his debates with the likes of Holbach, Diderot, and Naigeon precisely in terms of whether order could be the product of chance. Indeed, Rousseau put many of Lucretius’s (and Lamy’s) explicit arguments in the mouths of his atheistic interlocutors, in particular the argument that nature had produced many monstrous forms incapable of survival and reproduction, such that we were only seeing the survivors.

In Holbach’s Systeme de la nature (1770), all that we meant by “order” was a moment of natural configuration conducive to our human survival and happiness. All that we meant by “disorder” was a natural configuration conducive to our destruction or suffering. For Naigeon, writing in his Philosophie ancienne et moderne (1791-1794) against Francis Bacon’s argument from design, experience disclosed that there was nothing inherently “beautiful” or “horrible” in nature. For human beings who “coexist” successfully with nature, the universe appears a lovely example of art and design; for those who “coexist” painfully with the universe, the very same sequence of eternal causes and effects will appear dark and imperfect. The beings who coexist today will pass away as conditions change, Naigeon concluded, and no one could predict what new forms of material being would emerge. Denis Diderot’s Rêve de d’Alembert speculated that given time, natural processes had generated and would generate an extraordinary diversity of forms, only some of which would be fitted for survival.

On August 18, 1770, the parlement de Paris condemned the Système de la nature, known to contemporaries as “the Bible of atheism.” It proclaimed that its author had “revived” and “expanded upon” the “system of Lucretius.” It may have missed many the intervening steps, but it got the heart of it essentially right.