[Originally published as the first part of Irreducible Complexity]
One of the many scientific lines of evidence against neo-Darwinian evolution involves the concept of irreducible complexity.
Microbes, plants, fungi, animals, and human beings all have bodies that are composed of extremely complex microscopic machinery. The different parts of a biological cell are interdependent. That is, each part of the cell depends on all the other parts of the cell in order to function properly. Remove any one essential part, and the cell dies.
Hence, the cell is not just complex; it is irreducibly complex.
That is, it cannot be reduced to a simpler functioning cell by removing any essential component. Yet, neo-Darwinian evolution requires that all life came about from simpler forms, with new components added over the course of time by mutations. Hence, neo-Darwinian evolution is incompatible with irreducible complexity.
The Fingerprint of Intelligence
Irreducible complexity is a mark of intelligent forethought. Manmade machines almost always exhibit irreducible complexity.
Consider an automobile.
It has many interdependent parts that work together to accomplish a goal—in this case, to provide transportation for people and property. If you remove any essential part (the engine, the wheels, the drivetrain, the transmission, the steering wheel, the fuel tank, etc.) then the vehicle will not be able to do what it was designed to do.
Of course, not all parts of an automobile are essential.
You could remove the radio, the glovebox, the USB port, the indoor lights, the air-conditioning system, and the vehicle could still get you from point A to point B.
Certain other features could also be removed that result in reduced functionality. You could remove the windshield wipers and still get from A to B, but only in good weather. You could remove the headlights and still get from A to B, but only during the day (and not legally). You could remove the muffler and the car would still function (until your neighbors call the police).
But there are certain essential parts that cannot be removed without rendering the vehicle incapable of transportation. Hence, the vehicle does have irreducible complexity.
Irreducible complexity is always the result of a mental process of conscious planning. No one part of an automobile can, by itself, transport people from one arbitrary location to another. It takes creative thought to design a system in which multiple parts will work interdependently to achieve a common goal. The process requires understanding how each part functions, and then planning a system in which the parts are connected to each other to achieve the desired function.
Only when all the essential parts are assembled in the correct relationships is the system able to do what it was designed to do.
Can Such Complexity Evolve?
Suppose someone claimed that automobiles were not designed or built by people, but rather came about by a mindless, evolutionary process over millions of years.
Suppose the person argues that millions of years ago, a gear somehow evolved, then another gear, and then a driveshaft, and then a transmission, and so on. Some of these parts then fell together in ways that increasingly resembled a modern vehicle. Of course, many parts did not fall together in correct ways, but these were discarded as useless. But those rare combinations that worked were preserved because they provided some modest transportation benefit until vehicles gradually became the fully useful forms we see today.
Is such a scenario realistic?
Hardly. At no stage in such a hypothetical process would such a proto-vehicle be even remotely useful as a form of transportation until all the essential parts were present in the correct configuration.
What good are a driveshaft and two gears? Two percent of a vehicle will not give you a two percent advantage in getting from A to B. In fact, it would actually be harder to get from A to B if you had to carry two gears and a driveshaft. At such a stage, they are a detriment to travel and would be discarded.
Nor will 50% of the essential components of a car give you any advantage whatsoever in getting from A to B. A vehicle cannot function as a vehicle unless all its essential parts are present.
Therefore, irreducibly complex systems cannot come about by a mindless, evolutionary process in which each part is added one at a time to an already functioning system. This is because the system does not function unless all the essential parts are already there. Two percent, or fifty percent, or even ninety-nine percent of the essentials of a functional vehicle provide no transportation advantage whatsoever. The machine must have all its essential components to be useful.
A Challenge to Evolution
The design of living organisms is far more sophisticated and complex than any automobile. This should suggest that the Designer is far more intelligent than any human.
But is this complexity irreducible? Does it have certain essential features that are interdependent such that if any one is removed the system fails? If so, then it cannot have come about by an evolutionary process, where each stage is a functional organism that has only one improvement over its predecessor. Not all traits of all creatures are necessarily irreducibly complex. But the existence of even one such trait is inconsistent with neo-Darwinian evolution.