The original development of the argument from design was in reaction to atomistic, explicitly non-teleological, understandings of nature. Socrates, as reported by Plato and Xenophon, was reacting to such natural philosophers. While less has survived from the debates of the Hellenistic and Roman eras, it is clear from sources such as Cicero and Lucretius, that debate continued for generations, and several of the striking metaphors used to still today such as the unseen watchmaker, and the infinite monkey theorem, have their roots in this period. While the Stoics became the most well-known proponents of the argument from design, the atomistic counter arguments were refined most famously by the Epicureans. On the one hand they criticized the evidence for there being evidence of an intelligent design to nature, and the logic of the Stoics. On the defensive side, they were faced with the challenge of explaining how un-directed chance can cause something which appears to be a rational order. Much this defence revolved around arguments such as the infinite monkey metaphor. Democritus, had already apparently used such arguments in the time of Socrates, saying that there will be infinite planets, and only some having an order like the planet we know. But the Epicureans refined this argument, by proposing that the actual number of types of atoms in nature is small, not infinite, making it less coincidental that after a long period of time, certain orderly outcomes will result.
These were not the only positions held in classical times. A more complex position also continued to be held by some schools, such as the Neoplatonists, who, like Plato and Aristotle, insisted that Nature did indeed have a rational order, but were concerned about how to describe the way in which this rational order is caused. According to Plotinus for example, Plato’s metaphor of a craftsman should be seen only as a metaphor, and Plato should be understood as agreeing with Aristotle that the rational order in nature works through a form of causation unlike everyday causation. In fact, according to this proposal each thing already has its own nature, fitting into a rational order, whereby the thing itself is “in need of, and directed towards, what is higher or better”.
Louis Loeb writes that David Hume, in his Enquiry, “insists that inductive inference cannot justify belief in extended objects.” Loeb also quotes Hume as writing:
It is only when two species of objects are found to be constantly conjoined, that we can infer the one from the other . . . If experience and observation and analogy be, indeed, the only guides which we can reasonably follow in inference of this nature; both the effect and cause must bear a similarity and resemblance to other effects and causes . . . which we have found, in many instances, to be conjoined with another . . . [The proponents of the argument] always suppose the universe, an effect quite singular and unparalleled, to be the proof of a Deity, a cause no less singular and unparalleled.
Loeb notes that “we observe neither God nor other universes, and hence no conjunction involving them. There is no observed conjunction to ground an inference either to extended objects or to God, as unobserved causes.”
Hume also presented a criticism of the argument in his Dialogues Concerning Natural Religion. The character Philo, a religious sceptic, voices Hume’s criticisms of the argument. He argues that the design argument is built upon a faulty analogy as, unlike with man-made objects, we have not witnessed the design of a universe, so do not know whether the universe was the result of design. Moreover, the size of the universe makes the analogy problematic: although our experience of the universe is of order, there may be chaos in other parts of the universe. Philo argues:
A very small part of this great system, during a very short time, is very imperfectly discovered to us; and do we thence pronounce decisively concerning the origin of the whole?— David Hume, Dialogues 2
Philo also proposes that the order in nature may be due to nature alone. If nature contains a principle of order within it, the need for a designer is removed. Philo argues that even if the universe is indeed designed, it is unreasonable to justify the conclusion that the designer must be an omnipotent, omniscient, benevolent God – the God of classical theism. It is impossible, he argues, to infer the perfect nature of a creator from the nature of its creation. Philo argues that the designer may have been defective or otherwise imperfect, suggesting that the universe may have been a poor first attempt at design. Hume also pointed out that the argument does not necessarily lead to the existence of one God: “why may not several deities combine in contriving and framing the world?” (p. 108).
Wesley C. Salmon developed Hume’s insights, arguing that all things in the universe which exhibit order are, to our knowledge, created by material, imperfect, finite beings or forces. He also argued that there are no known instances of an immaterial, perfect, infinite being creating anything. Using the probability calculus of Bayes Theorem, Salmon concludes that it is very improbable that the universe was created by the type of intelligent being theists argue for.
Nancy Cartwright accuses Salmon of begging the question. One piece of evidence he uses in his probabilistic argument – that atoms and molecules are not caused by design – is equivalent to the conclusion he draws, that the universe is probably not caused by design. The atoms and molecules are what the universe is made up of and whose origins are at issue. Therefore, they cannot be used as evidence against the theistic conclusion.
Referring to it as the physico-theological proof, Immanuel Kant discussed the teleological argument in his Critique of Pure Reason. Even though he referred to it as “the oldest, clearest and most appropriate to human reason”, he nevertheless rejected it, heading section VI with the words, “On the impossibility of a physico-theological proof”. In accepting some of Hume’s criticisms, Kant wrote that the argument “proves at most intelligence only in the arrangement of the ‘matter’ of the universe, and hence the existence not of a ‘Supreme Being’, but of an ‘Architect’.” Using the argument to try to prove the existence of God required “a concealed appeal to the Ontological argument.”
Does not prove the existence of God
… from this sole argument I cannot conclude anything further than that it is probable that an intelligent and superior being has skillfully prepared and fashioned the matter. I cannot conclude from that alone that this being has made matter out of nothing and that he is infinite in every sense.— Voltaire, Traité de métaphysique
Søren Kierkegaard questioned the existence of God, rejecting all rational arguments for God’s existence (including the teleological argument) on the grounds that reason is inevitably accompanied by doubt. He proposed that the argument from design does not take into consideration future events which may serve to undermine the proof of God’s existence: the argument would never finish proving God’s existence. In the Philosophical Fragments, Kierkegaard writes:
The works of God are such that only God can perform them. Just so, but where then are the works of the God? The works from which I would deduce his existence are not directly and immediately given. The wisdom in nature, the goodness, the wisdom in the governance of the world — are all these manifest, perhaps, upon the very face of things? Are we not here confronted with the most terrible temptations to doubt, and is it not impossible finally to dispose of all these doubts? But from such an order of things I will surely not attempt to prove God’s existence; and even if I began I would never finish, and would in addition have to live constantly in suspense, lest something so terrible should suddenly happen that my bit of proof would be demolished.— Søren Kierkegaard, Philosophical Fragments
Argument from improbability
Richard Dawkins is harshly critical of theology, creationism and intelligent design in his book The God Delusion. In this book, he contends that an appeal to intelligent design can provide no explanation for biology because it not only begs the question of the designer’s own origin but raises additional questions: an intelligent designer must itself be far more complex and difficult to explain than anything it is capable of designing. He believes the chances of life arising on a planet like the Earth are many orders of magnitude less probable than most people would think, but the anthropic principle effectively counters skepticism with regard to improbability. For example, Fred Hoyle suggested that potential for life on Earth was no more probable than a Boeing 747 being assembled by a hurricane from the scrapyard. Dawkins argues that a one-time event is indeed subject to improbability but once under way, natural selection itself is nothing like random chance. Furthermore, he refers to his counter argument to the argument from improbability by that same name:
The argument from improbability is the big one. In the traditional guise of the argument from design, it is easily today’s most popular argument offered in favour of the existence of God and it is seen, by an amazingly large number of theists, as completely and utterly convincing. It is indeed a very strong and, I suspect, unanswerable argument—but in precisely the opposite direction from the theist’s intention. The argument from improbability, properly deployed, comes close to proving that God does not exist. My name for the statistical demonstration that God almost certainly does not exist is the Ultimate Boeing 747 gambit.
The creationist misappropriation of the argument from improbability always takes the same general form, and it doesn’t make any difference… [if called] ‘intelligent design’ (ID). Some observed phenomenon—often a living creature or one of its more complex organs, but it could be anything from a molecule up to the universe itself—is correctly extolled as statistically improbable. Sometimes the language of information theory is used: the Darwinian is challenged to explain the source all the information in living matter, in the technical sense of information content as a measure of improbability or ‘surprise value’… However statistically improbable the entity you seek to explain by invoking a designer, the designer himself has got to be at least as improbable. God is the Ultimate Boeing 747.
…The whole argument turns on the familiar question ‘Who made God?’… A designer God cannot be used to explain organized complexity because any God capable of designing anything would have to be complex enough to demand the same kind of explanation in his own right. God presents an infinite regress from which he cannot help us to escape. This argument… demonstrates that God, though not technically disprovable, is very very improbable indeed.— Richard Dawkins, The God Delusion
Dawkins considered the argument from improbability to be “much more powerful” than the teleological argument, or argument from design, although he sometimes implies the terms are used interchangeably. He paraphrases St.Thomas’ teleological argument as follows: “Things in the world, especially living things, look as though they have been designed. Nothing that we know looks designed unless it is designed. Therefore there must have been a designer, and we call him God.” 
A flawed argument
George H. Smith, in his book Atheism: The Case Against God, points out what he considers to be a flaw in the argument from design:
Now consider the idea that nature itself is the product of design. How could this be demonstrated? Nature… provides the basis of comparison by which we distinguish between designed objects and natural objects. We are able to infer the presence of design only to the extent that the characteristics of an object differ from natural characteristics. Therefore, to claim that nature as a whole was designed is to destroy the basis by which we differentiate between artifacts and natural objects.
Perception of purpose in biology
The philosopher of biology Michael Ruse has argued that Darwin treated the structure of organisms as if they had a purpose: “the organism-as-if-it-were-designed-by God picture was absolutely central to Darwin’s thinking in 1862, as it always had been.” He refers to this as “the metaphor of design … Organisms give the appearance of being designed, and thanks to Charles Darwin’s discovery of natural selection we know why this is true.” In his review of Ruse’s book, R.J. Richards writes, “Biologists quite routinely refer to the design of organisms and their traits, but properly speaking it’s apparent design to which they refer – an “as if” design.” Robert Foley refers to this as “the illusion of purpose, design, and progress.” He adds, “there is no purpose in a fundamentally causative manner in evolution but that the processes of selection and adaptation give the illusion of purpose through the utter functionality and designed nature of the biological world.
Richard Dawkins suggests that while biology can at first seem to be purposeful and ordered, upon closer inspection its true function becomes questionable. Dawkins rejects the claim that biology serves any designed function, claiming rather that biology only mimics such purpose. In his book The Blind Watchmaker, Dawkins states that animals are the most complex things in the known universe: “Biology is the study of complicated things that give the appearance of having been designed for a purpose.” He argues that natural selection should suffice as an explanation of biological complexity without recourse to divine provenance.
However, theologian Alister McGrath has pointed out that the fine-tuning of carbon is even responsible for nature’s ability to tune itself to any degree.
[The entire biological] evolutionary process depends upon the unusual chemistry of carbon, which allows it to bond to itself, as well as other elements, creating highly complex molecules that are stable over prevailing terrestrial temperatures, and are capable of conveying genetic information (especially DNA). […] Whereas it might be argued that nature creates its own fine-tuning, this can only be done if the primordial constituents of the universe are such that an evolutionary process can be initiated. The unique chemistry of carbon is the ultimate foundation of the capacity of nature to tune itself.
Proponents of intelligent design creationism, such as William A. Dembski question the philosophical assumptions made by critics with regard to what a designer would or would not do. Dembski claims that such arguments are not merely beyond the purview of science: often they are tacitly or overtly theological while failing to provide a serious analysis of the hypothetical objective’s relative merit. Some critics, such as Stephen Jay Gould suggest that any purported ‘cosmic’ designer would only produce optimal designs, while there are numerous biological criticisms to demonstrate that such an ideal is manifestly untenable. Against these ideas, Dembski characterizes both Dawkins’ and Gould’s argument as a rhetorical straw man. He suggests a principle of constrained optimization more realistically describes the best any designer could hope to achieve:
Not knowing the objectives of the designer, Gould was in no position to say whether the designer proposed a faulty compromise among those objectives… In criticizing design, biologists tend to place a premium on functionalities of individual organisms and see design as optimal to the degree that those individual functionalities are maximized. But higher-order designs of entire ecosystems might require lower-order designs of individual organisms to fall short of maximal function.— William A. Dembski, The Design Revolution: Answering the Toughest Questions About Intelligent Design
The teleological argument assumes that one can infer the existence of intelligent design merely by examination, and because life is reminiscent of something a human might design, it too must have been designed. However, considering “snowflakes and crystals of certain salts”, “[i]n no case do we find intelligence”. “There are other ways that order and design can come about” such as by “purely physical forces”. 
The design claim can be challenged as an argument from analogy. Supporters of design suggest that natural objects and man-made objects have many similar properties, and man-made objects have a designer. Therefore, it is probable that natural objects must be designed as well. However, proponents must demonstrate that all the available evidence has been taken into account. Eric Rust argues that, when speaking of familiar objects such as watches, “we have a basis to make an inference from such an object to its designer”. However, the “universe is a unique and isolated case” and we have nothing to compare it with, so “we have no basis for making an inference such as we can with individual objects. … We have no basis for applying to the whole universe what may hold of constituent elements in the universe.”
Most professional biologists support the modern evolutionary synthesis, not merely as an alternative explanation for the complexity of life but a better explanation with more supporting evidence. Living organisms obey the same physical laws as inanimate objects. Over very long periods of time self-replicating structures arose and later formed DNA.