Specified complexity

Specified complexity is a concept developed by mathematician, philosopher, and theologian William Dembski. It is commonly presented as part of the critique of natural selection put forward by the intelligent design movement, with which Dembski is associated. The term "specified complexity" was originally coined by origin of life researcher Leslie Orgel, and later employed by physicist Paul Davies in a similar manner, to denote what distinguishes living things from non-living things"

"In brief, living organisms are distinguished by their ‘’specified‘’ complexity. Crystals are usually taken as the prototypes of simple well-specified structures, because they consist of a very large number of identical molecules packed together in a uniform way. Lumps of granite or random mixtures of polymers are examples of structures which are complex but not specified. The crystals fail to qualify as living because they lack complexity; the mixtures of polymers fail to qualify because they lack specificity." (L. Orgel, The Origins of Life, 1973, p. 189)

Dembski uses specified complexity in a similar manner, to denote a property that makes living things unique. He claims that specified complexity is present when there exists a large amount of specified information. The following examples demonstrate the concept of specified information:.

High information, low specificity. For example, the 10-letter structure "dkownl el." According to Shannon’s theory of information, a random string of letters contains the highest possible information content, because it cannot be compressed into a smaller string. However, the random nature makes the string without meaning, and thus non-specified according to Dembski. (Note that “meaning” does not play a role in Shannon information theory.)

High specificity, low information. For example, the 10-letter structure "aaaaaaaaaa." The sequence has low information because it can be compressed into a smaller string, namely “10 a’s” . However, because it conforms to a pattern it is highly specified.

Specified information. For example, the 10-letter structure "I love you". This has both high information content, because it cannot be compressed, and specificity, because it conforms to a pattern (grammar and syntax). In this case, the pattern it conforms to is that of a meaningful English phrase, one of a selection of strings which together make up a small fraction of all possible arrangements. In living things, the “pattern” that molecular sequences conform to is that of a functional biological molecule, which make up only a small fraction of all possible molecules.

Dembski defines complex specified information (CSI) as something containing a large amount of specified information, which has a low probability of occurring by chance. He defines this probability as 1 in 10150, which he calls the universal probability bound. Anything below this bound has CSI. The terms "specified complexity" and "complex specified information" are used interchangably.

Dembski and other proponents of ID assert that specified complexity cannot come about by natural means, and is therefore a reliable indicator of design. Dembski has formulated this as his Law of Conservation of Information:

"This strong proscriptive claim, that natural causes can only transmit CSI but never originate it, I call the Law of Conservation of Information.

Immediate corollaries of the proposed law are the following:

(1) The CSI in a closed system of natural causes remains constant or decreases.

(2) CSI cannot be generated spontaneously, originate endogenously or organize itself (as these terms are used in origins-of-life research).

(3) The CSI in a closed system of natural causes either has been in the system eternally or was at some point added exogenously (implying that the system, though now closed, was not always closed).

(4) In particular any closed system of natural causes that is also of finite duration received whatever CSI it contains before it became a closed system."(Intelligent Design: The Bridge Between Science & Theology, InterVarsity Press, 1999, pg. 170)