The design argument seeks to prove the existence of God by comparing the universe to a machine. At first this seems plausible. However, with further investigation, the analogy fails. There is certainly order in the universe, just as in a machine, but it is a different sort of order, and doesn't require a designer. Further, the argument fails to prove the existence of a single all-knowing, all-powerful, and all-good deity.
The design argument purports to prove the existence of an omniscient, omnipotent, omnibenevolent, and human-like God by analogy. It states that if we look at a creation of humans, such as a watch, house, or computer we can tell that it has a purpose and a designer. If we then look at the world or the universe we can see that it has order, various parts all work in cooperation, and it produces effects. Since the universe appears much like a creation of humans, though much superior and on a much grander scale, the universe must have a designer, who is God.
There are two main assertions in this analogy. The first is that order and functionality imply design; the second that the universe resembles human creations. Both of these assertions are flawed.
First of all, a distinction must be made between function and purpose. Towels, for instance, have the purpose of drying people off. They may be used, however, for many different functions such as a folded as a mat for sitting on the grass, draped over your head to block the sun from your face as you take a nap, wrapped as an emergency bandage, wetted for use in hand to hand combat, etc., etc. None of these functions are the purpose for which the towel was designed, but for someone who knew nothing about towels, they might seem to be the purpose.
Similarly, objects can have function without purpose. If I were to stoop down and pick up a stone I could use it for a number of things. I could crack shells, I could throw it at politicians I don't like, I could carve runes into it, or I could weigh a piece of paper down with it. Was the stone designed for this or any other purpose? No, the stone started as molten rock in the earth. It then changed form by rolling down hills, being washed by rivers, etc. It was not designed, much less does it have a purpose, but it has many functions. In short, we cannot deduce that an object has a designer merely because it performs a function.
Does order imply design? Take the human body, for instance. It has order: the heart, the brain, the blood, the nerves, the bones and muscles all work together in a complex system. Various parts of the whole even have certain functions: the heart provides blood to the rest of the body, the brain tells the body what to do, the stomach digests food to give the body energy, and so on. Yet was the human body designed? No, it evolved, through a long process, from single-celled organisms.
Clouds are another example of objects with order and function, but without design. Clouds certainly have order. Clouds behave in certain ways under certain conditions of temperature and humidity. Clouds have visual order which can be described and distinguished from other types of clouds. They have function: they provide rain and snow, they relieve the heat of a hot summer's day, they give people interesting things to stare at, etc. They do not, however, have purpose. Regardless of whether God designed the process of how clouds are created, individual clouds happen without intention. We cannot accurately predict the presence or the state of a cloud very far in advance. We cannot, for instance, declare that such and such a cloud will have rained some number of times in these places and snowed in those places over a period of a few weeks. Nor can we say, "In three weeks there will be a cumulus cloud right over this spot." This inability for prediction is not due to our lack of meteorological knowledge, it's due to the large number of random factors. Will these winds continue to blow? Will this hot air system run across that cold air system? How much moisture will there be in this area? The cloud changes and develops over time due to these random factors.
The Earth seems to have undergone development in a similar way to the human body or the cloud, starting as a hot planet bombarded by space debris, then developing an atmosphere, then less harsh land conditions, then larger and larger organisms, and so on. Most of the major changes have been due to random events. From what we can tell, the universe has probably undergone a similar process, beginning in a large burst, then various stars coalesced, debris became planets, and so on.
Ecosystems too seem to develop in the same way. It is possible that God designed each and every aspect of each and every planet, taking adaptation into account. It is more plausible and there is sufficient evidence that the presence of the climate, soil, terrain, etc. is the reason that the current plants exist and not others that have tried to grow. The animals that live in the system exist there because they are the ones which thrive in the environment, the ones which have evolved there. In other words, the ecosystem produces itself, without need of God, and does not have design or purpose, though it does have order and function.
Some defenders of the design argument might argue that God designed the evolution of humans, of ecosystems, of Earth, of the universe. They would say that God designed the first amoeba with the intent that it would evolve into a larger organism, develop this and that feature, and eventually become human. First, this objection just adds complexity to the issue. While it is possible that God did this deed, it is much more likely that humans have evolved without the intent of any god, since there appears to be no need of a god for humans to evolve. Asserting that it is divine design is similar to arguing that we can't believe what we see because an evil demon is playing with our minds. There is less evidence for that position and it is more complicated and less believable.
The second problem with the objection is the fact that it doesn't stick to the original argument. The original design argument stated that the universe must have a designer because it resembles human creations which clearly have a designer. There are no human creations which are designed to begin as one thing and then, through a complex process which takes place over a long time, end up as something much different. Everything that humans design is designed for a present need, not so that it will evolve into an object for an unseen or distant purpose. Nor do we design objects with the intent that some random event will inspire someone else to create or invent a way to use the object in a different manner. Even though this does happen with things like paper clips and towels, it is not the intent of the designer.
The second assertion of the design argument is that the universe is similar to human creations. However, the universe does not resemble human creations very closely. Certainly various parts of the universe function well, have complex parts and systems, and seem to have a purpose. However, they do not do these things in the same way that, for instance, a watch does. Ecosystems, for example, work well and have complex parts and functions. Certain climate, soil, terrain, etc. exist and some plants take root in it. Plants that can adapt to the climate thrive, animals enter onto the scene. Certain animals are able to live and thrive in the climate, others die quickly. Those which survive pass on traits that better suit the climate. As herbivores begin to thrive and over-populate they either begin to die off due to lack of food, they get sick, or they get taken down by predators. Did these animals, these plants, come into this system in the same way that a human puts parts into a computer? No, the animals came because they were looking for a place to live where they could find adequate food, where it wasn't too hot or cold, where the terrain suited their body, etc. Once in the ecosystem, the species that adapt to its specific quirks have the greatest edge for survival. When humans design things which have adapted parts a new object must be designed each time a part gets better. The parts in a machine don't slowly function better in the machine.
A defender of the design argument might object that ecosystems and other similar systems are analogous to some human creations. For instance, when a neighborhood in a city is designed, the planner looks at natural factors and puts certain types of houses there. He also considers what types of businesses can help and be helped by the people that the neighborhood is intended for. The defender of the design argument would say that God designed ecosystems in a similar way.
The main problem with this objection is that you have to have previous knowledge of the neighborhood to say whether or not it was designed. Many neighborhoods are designed at one time, while others start as a few houses, a business or two enters the area, more houses come from a different developer, the city places a park, still more houses come and businesses come in from yet another developer, etc. So since neighborhoods can both evolve and be designed, what reason do we have to believe that the universe was designed rather than merely evolved?
The point of the design argument is to prove the existence of a single omniscient, omnipotent, omnibenevolent God. Even if the universe was designed, it wouldn't have to be by a single god. London, for instance, was certainly created by people. It is full of buildings, systems, and objects made by people. However, all these things were designed, made, and put into place by different people over several hundred years. Someone designed this building, someone else that neighborhood, someone else the transportation systems. Various parts have quite definite purposes, and the city as a whole can be seen to have the purpose of a place to live and work, though this is no more than the sum of the individual functions that London serves to the people there. The question "who designed London" is clearly absurd. Romans built the first few structures in the location of London, Saxons built more, various people designed parts of its growth, but no single person, not even a group of people, said at any point "I will design this city so that it will end up like this and will produce these effects." The city has had millions of designers and builders working continuously, not a single designer who created it once.
Some people might object to this by argument saying that London is not like things such as watches and houses which the original analogy was based on. However, a city is a better analogy to an ecosystem, the Earth, or the universe than a watch is. Each part in a watch leads to a single function, telling time. Springs turn gears which turn the hands, the glass on top is so that we can see the hands, the casing is to protect the mechanism so that it can reliably tell the time. A city, on the other hand, doesn't have a specific purpose. Each person who lives and works in the city has certain intentions that she wants the city to fulfill, but there is no overall purpose to a city, rather it serves many functions and acts as a place for people to live, work, and trade. Does the whole universe work towards one end like a watch, or do various parts each have their own separate intentions and functions which are not directly related to the other parts?
The design argument fails to prove the existence of a single omnipotent, omniscient, omnibenevolent, human-like God. Even if the universe was designed and created all at once a long time ago, it could have been by forces other than the God under consideration. For instance, it could have been a joint project by many stellar beings, none of whom are all-knowing, all-powerful, etc. One part of the standard design argument is that since the universe resembles human objects, the creator must have a human-like mind. This is not so. It is possible that the creator has a completely different mind, but even if it has similarity, our minds are more likely god-like than its mind human-like, just as a baby is human-like, but humans are not baby-like (due to magnitude and development).
The assumption that the universe was designed says nothing for omniscience or omnipotence. Clearly, in order to design a universe this vast, one must know a lot and be very powerful, but it could quite easily be the result of finite power and knowledge. Humans often make very large and complex creations, so a finite universe (ours is quite possibly finite) could be a very complex work of a vast yet finite god.
And who can say that the designer is benevolent? The universe could have been created just to torture some planets that were lying around, or so the god could be mean to some other god, or just on a whim. God could have created the universe with good intentions, evil intentions, or just to see what would happen, either evil or good.
So while the design argument may seem convincing at first, it doesn't hold up to close scrutiny. The analogy is flawed in that it fails to show that order and function imply design and that the universe resembles human creations. Further, even if the universe was created by a god, the argument fails to show that It is all-knowing, all-powerful, all-good, or human-like.