In this section, Philo continues to develop possible alternatives to the machine analogy. The world as we know it, he boldly claims, might be the result of a chance arrangements of atoms. Perhaps atoms move around chaotically in various states of disorder (as he puts it, matter is thrown into various arrangements by "blind, unguided force"). By sheer chance these randomly moving atoms might happen to combine now and then into orderly structures. These orderly structures might then persist despite the forces of change operating on them because the very orderliness of the structures might confer special survival advantages. This model, he tells us, is a modified version of the old Epicurean system, and it seems to be the most plausible candidate for a true cosmogony.
Demea's objection to this revolutionary idea is to point out that it would require matter to have motion in it without any first mover or motive agent putting this motion into the system. In response Philo says that it is no easier to understand how motion can simply exist in matter than it is to understand how motion can be transmitted from mind to matter. Perhaps, he posits, there was always motion within the matter. This same stock of motion might persist eternally, and, get propagated between pieces of matter by impulse.
Cleanthes also has an objection. There is a problem with this theory, he says: it does not explain why our world is so much better than it would need to be for the mere survival of the ordered structures (i.e. for the survival of each individual species and object). The world does not have the bare minimum level of order that we need to survive, but rather it has much more than that. We could have done without eyes and ears, for instance. We could also have done without horses or camels in the desert or a loadstone to help guide our journeys. Yet these make our lives so much better. They must, therefore, indicate the presence of a benevolent designer who had our comfort in mind.
Philo admits that his system has not been worked out perfectly; he has no way to account for these added benefits of the system. However, he points out that Cleanthes' theory also suffers from many slight inconsistencies. For instance, we have never, in all of our experience, seen thought move pieces of matter that were not connected to the thought as a body to mind. It is easy to find problems with all cosmological systems, he tells his friends. That is why skepticism always triumphs—because when it comes to the subjects of natural religion and the origin of the world (subjects where our experience does not reach) there is simply not enough evidence to sufficiently support any theories.
In this section Philo presents exactly what he was demanding in part IV: a cosmogonic theory that would not only fit the evidence provided by the universe, but would actually explain that evidence. Philo's modified Epicurean picture posits a principle that actually gives an illuminating and logical account of how the order we observe around us might have arisen. The explanation is illuminating because it appeals to a general, plausible principle: that order might confer survival advantages on objects that possess it. The design argument, on the other hand, is not illuminating because it just appeals to another particular, very mysterious event: God designed the world.
The theory that Philo presents will sound strikingly familiar to modern readers, since it bears a strong resemblance to Darwin's theory of natural selection. One plausible reason our world might be ordered, Philo tells us, might be that all the disordered arrangements did not survive; order might confer survival advantage. To put it in more familiar terms, the fittest survive, and the more ordered are the more fit.
Philo's version of the theory is not nearly as well described as Darwin's, of course, and this is why he cannot defend it against Cleanthes's objection. He cannot explain why our world is so much better than it needs to be. Darwin, however, could explain this phenomenon. In Darwin's theory, every new mutation that arises (what Philo would call new arrangements of atoms) can either confer survival advantage or not. If it does then it will probably persist in the species because the mutated member will be more likely to reproduce than other members of the species, and so his mutated material will be passed on. Darwin does not focus on order itself as a property like Philo does; instead he realizes that what needs to be explained is each of the features of a species that together compose the appearance of order. It is not order that is selected for, in other words, but rather what is selected for is all of the particular features that together make for an ordered system.