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 the 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 on 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 is 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 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. 2% or 50% or even 99% 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.
Consider the circulatory system. It has a system of arteries, veins, and capillaries, each of which contains blood cells and blood plasma. It includes a heart that pumps the blood. Some of the blood vessels also pass through respiratory organs (either lungs or gills depending on the organism) where the blood releases carbon dioxide and receives oxygen. Each part depends upon all the others. Remove any one of these parts and the organism dies.
When considering the hypothetical evolution of any complex system, it is helpful to ask two questions. First, which essential part evolved first? Second, which essential part evolved last? In the circulatory system, which evolved first – the heart or blood vessels? Without one, the other is useless. Did blood cells evolve before or after blood plasma? Without plasma, the blood cells cannot move properly. But plasma does not have the oxygen transporting capacity of blood cells. Each is useless without the other.
Evolutionists may argue that all these systems evolved from simpler versions. But even the simplest system of its kind must have something like a heart to move the blood, blood to be moved, plasma to make the blood mobile, and some way of exchanging carbon dioxide for oxygen from the environment. Each system requires at least a basic version of the others in order to function. So which part evolved first? None. Each is useless by itself. Which part evolved last? None. Without all these parts the organism dies.
Sometimes an evolutionist will claim that natural selection can overcome such obstacles. Natural selection refers to the observation that organisms best suited to their environment tend to survive and reproduce in greater numbers than those organisms less suited to that environment. In extreme cases, the organisms less suited can be driven to extinction. We have many observations that confirm this reality. But this is not a creative process. Natural selection does not create any new traits. It simply refers to the reduction or removal of organisms with traits that are not already suited to the environment. Upon careful reflection, we will find that natural selection actually prevents neo-Darwinian evolution from occurring.
One severe problem with evolutionary scenarios of complex systems is that some necessary intermediate steps would have a detrimental effect on survival, and would tend to be eliminated. Consider the first organisms to evolve a circulatory system. Which part evolved first? If a primitive heart evolves first, then it has no blood to pump, and is useless. Yet the organism would have to maintain and supply nutrients to this new, useless organ, which takes energy. This has a negative impact on survival. In other words, organisms without the useless organ would have a much higher probability of survival.
Natural selection has no foresight. It does not preserve traits that might become useful in the future, once other co-dependent traits have also evolved. No. It refers to the success of organisms that have useful traits right now, and the reduction or removal of organisms that do not have useful traits now. For this reason, natural selection cannot account for any irreducibly complex system.
An Example: Coagulation
One example is the blood clotting mechanism. This is a truly amazingly system of interdependent parts which prevents people from bleeding out every time they get a small cut in their skin. Blood platelets remain inactive when in the blood stream. But when the blood vessel is broken such that it is releasing blood, the platelets clump together and begin to “plug the leak.” The system of bio-chemistry by which this occurs is amazing and is well beyond the scope of this article. But consider just two aspects of this process.
First, there is a system of chemical checks and balances that prevents the platelets from clotting when inside a healthy blood vessel. Without that system, the blood would clot within all your blood vessels resulting in immediate death. Second, there is also a system that activates the platelets when they encounter a damaged blood vessel so that they clot together and plug the leak. Without this system platelets would not clot and would be useless. Furthermore, a person would be in danger of bleeding out any time he or she got a cut.
So, in the neo-Darwinian view, which evolved last – the platelets, the system that activates them at a vessel break, or the system that keeps them from activating in healthy blood vessels? Each system is either useless or deadly without the other two. Thus, these systems cannot have evolved in a neo-Darwinian fashion. Rather, each component is designed to work in concert with the other components.
Is Life Irreducibly Complex?
Charles Darwin wrote, “If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would break down. But I can find out no such case.” So, Darwin conceded that any genuinely irreducibly complex organ would falsify his idea of common decent. But he didn’t think that there were any examples. Now we have many. As biologists have studied living systems, we have found them to have far more interdependent components than Darwin could have imagined. Remove any essential component and the system fails.
Consider the “simplest” living cell. At minimum, a living cell contains DNA, enzymes that duplicate the DNA when the cell divides, enzymes that translate DNA to form mRNA, ribosomes that read the mRNA and synthesize proteins that allow the cell to function, and a cell membrane that holds these things together. Now, which of these components evolved first? Was it DNA? DNA by itself is useless. It does not have the capacity to produce proteins, or to duplicate itself. What about the mRNA? But mRNA is useless without the ribosomes that read it and produce proteins, including the very enzymes that translate DNA into mRNA. Was it the enzymes that duplicate the DNA? But these serve no purpose without DNA, and they cannot duplicate themselves. Was it the enzymes that translate DNA to form mRNA? These serve no purpose without DNA. Was it the ribosomes that produce proteins from instructions in the mRNA? But these are useless without the mRNA. The instructions to produce the enzymes that translate or replicate DNA are contained in the DNA which cannot function or multiply without them.
A functional self-replicating cell requires all these systems to be in place simultaneously. Therefore, a cell cannot have evolved in a neo-Darwinian stepwise fashion. The complexity of living cells was unknown in Darwin’s day. And we didn’t know nearly as much about the complexity of biological organs and systems. So, Darwin’s ignorance of the many examples of irreducible complexity is somewhat understandable given the time in which he lived. But today there is no excuse. We now understand much about how biological systems operate, and we have countless examples of irreducible complexity. Knowledge is the enemy of evolution. But all of this science only serves to confirm what Christians have known for millennia. Biblical creation is true.
 Due to the curse of sin, the blood clotting mechanism sometimes malfunctions and forms a blood clot within a healthy blood vessel, thereby preventing circulation in that vessel. This can result in serious damage or even death.
 Also due to the curse of sin, the blood clotting mechanism is damaged in some people, which reduces the ability of the platelets to clot around a cut. This condition is called hemophilia.
 Darwin, C., On the Origin of Species by means of Natural Selection, 6th edition, p. 154.