Updated: May 17
The mousetrap is a well-known illustration of the concept called “irreducible complexity” - the claim that certain features of an organism only function when all of its supplementary parts are perfectly developed and located precisely. Such features would be impossible to have gradually evolved out of randomness, as evolution demands. Incremental parts are useless alone, thereby natural selection has no reason to allow them to stay in the population.
Before we go further into the arguments for and against irreducible complexity, I think it would be beneficial to look into an actual biological example that exhibits irreducible complexity. After all, no mousetrap has ever evolved inside any living organisms.
Ever wonder how bacteria swim in watery environments to find food and escape from enemies? The bacteria use something called flagellum. It is no exaggeration to call it an advanced nanotechnological propeller that no scientists today can remotely create in the laboratory! Eight million of these propellors can easily fit on the end of a human hair. The debate over irreducible complexity has been more than twenty years, yet studies of flagellum from the engineering perspective have still been active up to at least a couple of years ago. Some even call the flagellum the most efficient machine in the Universe! The bacterial flagellum was quoted as a prime example of irreducible complexity right from the beginning.
Friends, this YouTube video should help you get an idea of what the bacterial flagellum looks like, and this other video speaks to the amazing functions of these little machines. It functions as a rotary engine that rotates a helical protein tail to propel the bacteria to move forward. Roughly speaking, it consists of a rotor, a stator, a driveshaft, bearings, and a tail-like structure as a propellor. The flagellum rotates 60 to 2000 turns per second - yet it can reverse its directions in a quarter turn. It allows the bacteria to travel 20 body lengths per second. That would be equivalent to a person swimming 120 feet per second.
How is the amazing flagellum related to our discussion of irreducible complexity or evolution? Well, there are around 30 to 40 different parts to make up the flagellum. Simply missing a miniscule part or a slight misplacement of any single part would render the whole structure useless. Natural selection would reject the existence of a 99% completed flagellum as it does not help survival. That means these 30 to 40 parts have to all come together and assembled perfectly at the same time in order to stay in the population. That is no Evolution at all.
A gradual evolutionary process does not seem remotely possible to create the flagellum, right? Our friends in the evolution camp would say: Absolutely not!