The Argument from Irreducible Complexity
Intelligent design argued that Darwinism could never account for certain forms of adaptation that we see in the natural world. What made intelligent design different from its forebears was its seeming scientific sophistication. Proponents of intelligent design were often well-qualified scientists and mathematicians, and they dressed up their arguments with the latest findings from microbiology and abstruse applications of probability theory.
Defining the Irreducibly Complex System
The basic idea is that certain natural phenomena, specifically features of biological organisms, display a property that cannot be accounted for by mainstream evolutionary theory. In Michael Behe’s case the relevant property is that of irreducible complexity. To understand this, we’ll need to look at Behe’s definition:
Irreducibly complex system (ICS) = Any single system which is composed of several well-matched, interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to cease functioning.
Examples of Irreducible Complexity
Behe’s favourite example is the bacterial flagellum. This is a thin, filament-like, appendage that protrudes from the cell membrane of many species of bacteria. It is used to help propel the bacteria through liquid. One of the remarkable features of a bacterial flagellum is that it functions like a rotary motor, where the flagellum is like a freely-rotating axle, supported by a complex assemblage of protein parts. Behe’s contention is that if you removed one component from the complex assemblage it would cease to function as a rotary motor.
A slightly more familiar example, and one also used by Behe, is a mousetrap (an old-fashioned, spring-loaded one). This is made up of fewer functional parts, but every one of them is essential if the mousetrap is going to perform its desired function. Thus, it is an ICS because if you remove one of the parts it ceases to function as intended.
| System | Functional Parts | Basic Function |
|---|---|---|
| Bacterial Flagellum | Protein parts, freely-rotating axle | Propel bacteria through liquid |
| Mousetrap | Spring-loaded mechanism components | Trapping and killing small vermin |
The Structure of the Argument
The following analysis helps to clarify the structure of the argument from irreducible complexity. That argument begins by identifying an ICS and then works like this:
- X is an irreducibly complex system.
- If X is an irreducibly complex system, then X must have been brought about by intelligent design.
- Therefore, X must have been intelligently designed.
Note that the use of the variable-term X is significant. While the bacterial flagellum is the most widely-discussed example, the idea behind the argument is that there are many such ICSs in nature and hence many things in need of an explanation in terms of intelligent agency.