Intelligent design is defined by the Discovery Institute as such:
“Intelligent design refers to a scientific research program as well as a community of scientists, philosophers and other scholars who seek evidence of design in nature. The theory of intelligent design holds that certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection. Through the study and analysis of a system's components, a design theorist is able to determine whether various natural structures are the product of chance, natural law, intelligent design, or some combination thereof. Such research is conducted by observing the types of information produced when intelligent agents act. Scientists then seek to find objects which have those same types of informational properties which we commonly know come from intelligence. Intelligent design has applied these scientific methods to detect design in irreducibly complex biological structures, the complex and specified information content in DNA, the life-sustaining physical architecture of the universe, and the geologically rapid origin of biological diversity in the fossil record during the Cambrian explosion approximately 530 million years ago.” - www.discovery.org
My argument concerns the “complex and specified information in DNA”, which is often shortened to “specified complexity”. Within DNA, we find extremely complex instructions that govern the behavior of all life on the molecular level. Such intelligent design proponents as Frank Turek (“I Don't Have Enough Faith To Be An Atheist”) liken the genetic code to the largest and most complex book ever written. The argument goes, if we recognize a written volume such as Hamlet to be the product of an intelligent mind, should we not conclude the same about a string of information many orders of magnitude greater than any of Shakespeare's classics? My answer is no.
The analogy to a written book is missing a crucial point, as are all analogies in which DNA is compared to any information produced by humans, such as a computer program or a musical composition. The difference lies in what I call “natural function”. This term refers to the ability of any string of information to interact in a meaningful and complex way with its environment. Now, “meaningful and complex” is rather vague, so let me give an example. If “I think, therefore I am” was drawn in the sand, its creator would not have to wait long before processes such as wind, waves, and the feet of the occasional passerby destroyed it. This is to be expected; given the specificity in which the grains of sand must be ordered to spell out “I think, therefore I am”, the arrangements in which those same grains of sand do not spell out Descartes's famous line (or any other words in the English language, for that matter) far outnumber the relatively small arrangements in which the sand will spell out the sentence. Entropy takes its toll, and we lose our “information”. Now, let us consider the inner workings of a cell. We observe its constant state of nonequilibrium, which defies our intuitions about how matter should behave when it is left alone. The information in DNA, unlike the writing in the sand, is preserved. How? Let's think about the medium in which this information is encoded: Nucleotides, held together by sugars and phosphates, where each sugar has a nucleobase attached which represents genetic “information”. These nucleobases come in four types, which are now referred to as G, A, T, and C. This information, unlike the writing in the sand which consisted of millions of particles which do not interact with each other in an individually distinct manner, is encoded in single molecules. Of what significance is this, and how does it refer to natural function? Well, each molecule behaves in a certain manner. It can interact in various ways with the basic constituents of life: atoms. (Carbon, as we know, composes the greatest variations of highly complex and diverse molecules.) Now we're getting somewhere: grains of sand do not interact with each other in the way that molecules do. Grains of sand do not cling to each other, possess net electric charges, or self-assemble into complex shapes, as we have observed with molecules in the famous Miller-Urey experiment.
Now comes the kicker: the dynamic, interactive nature of single atoms and molecules allow for something we do not see on a macro scale: the creation and sustenance of information. This information is granted, by the laws of physics, the ability to interact with other matter in a complex and dynamic way, by the medium in which it is contained. That is the difference between a string of information that possesses a natural function and one which does not: the information encoded in nucleobases can employ the laws of physics to directly interact with its environment. As I hope I have shown, it is not the information itself which we should be paying attention to: it is the medium in which it is encoded. If I were to write the genetic code for a simple virus on the side of a mountain, that mountain would not begin to devour its neighbors. Conversely, if I were to write out Hamlet as a complex sequence of nucleobases (assuming for the sake of argument that I invented a morse-code-esque system in which I could represent the entire alphabet through sequences of the four bases of DNA), it would most likely result in a rather muddled attempt at life. The information of life, unlike any book humans have ever written, is “readable” by Mother Nature herself- the laws of physics, in this case- and she has been reading it long before any of us came around. We would be right, therefore, to deduce that a certain string of information originated from an intelligent mind like ours if and only if that information only carried significance to intelligent minds- nothing else. The information of life, due to its dynamic medium of organic molecules, carries a natural significance to the laws of Nature which rings strong and clear.