A frequent complaint of the skeptic is the inconsistency of the ailments of the human body and the idea of an all-wise God having designed man. Back problems in humans are viewed as the result of man having been on four legs until recently and thus are viewed as the result of our evolution. A designing God would not have made man with a back so poorly designed for vertical posture. In a similar way, skeptics ask why our bones are not thicker so they would not break so easily, why we are not smaller so that we would need less food, why we have two breasts when we only need one, why are our organs so oversized.
These are interesting questions. It is true that humans can live with one-third the kidney mass that we have, half the intestinal length we have, and 10 times less pancreatic material than we have. Some mammals have 16 breasts and yet we have two. That leaves us with twice what is needed for one child and less than what is needed for triplets.
The challenge we are raising here is not just one-sided. From an evolutionary standpoint, it would seem that these same questions would raise problems. It takes more energy to operate the kidneys (gram for gram) than any other part of the body. Should the smallest possible kidney not be the more advantageous from an evolutionary standpoint? Certainly a pancreas which is 10 times the mass that is needed is a needless waste of space and energy in the body and makes the body more vulnerable. Bones made of stronger materials and made differently to be resistent to breaking would obviously offer an evolutionary advantage, and if backs are so poorly equipped for vertical travel and if man became erect millions of years ago, as modern evolutionists claim, why have our backs not evolved leaving us visibly different than our ancestors? No quantitative biological evolutionary explanation has been given to the questions of size, number, and strength of body parts; and natural selection would seem to favor different body configurations than we have.
The answer to these questions come from the field of engineering. Engineers deal with questions of how strong something should be, how big it should be, how many of them there should be, and where they should be. If you are building a 12-passenger airplane, how many safety exits should there be? Twelve might be the obvious answer, but putting 12 doors in an airplane would interfere with the structural safety and would make the plane unusable for transporting baggage. If you are building an elevator, how strong should the cable be? If you put a sign in the elevator that says "maximum load 1200 pounds," do you use a cable that will support 1201 pounds? Obviously you have to build a safety factor into the elevator problem. Not only do you have the fact that someone may put more than 1200 pounds in the elevator no matter what the sign says, but you also have to realize that wear, chemical action, and emergency situations may change what the cable can actually hold. You may even have to consider the value of what the elevator will be transporting. A passenger elevator will typically have a safety factor of 11 while a freight elevator will have a safety factor of 7. Costs, benefits, expected probability of the magnitude of variation of loads, etc., are all considered when designing things of this type. The laws of physics, chemistry, and economics are all used by engineers to accomplish this design, and every day you and I put incredible faith into the acceptance of the validity of their design.
In biological systems, there is just as much, if not more, of the same kind of designing required. First of all, the cost in terms of energy (in the form of ATP) to build and maintain the body parts has to be considered. Big organs take a lot of energy to build and take a lot of energy just to carry around. When my daughter was pregnant, she would frequently complain about how much extra energy was required to carry and supply the energy requirements of my much-looked-forward-to grandchild. The energy investment can be a lethal factor when food supplies are limited. In the winter of 1846-47, a group of pioneers got trapped by a snowstorm with limited food supplies in a place called Donner Pass. Half of the males, but only 5 percent of the females, died--the explanation seeming to be the size of the individuals and what energy was needed to sustain them.
Energy is just one of a huge number of variables that have to be designed into biological systems. In most mammals, the number of breasts is twice the average litter size. This means that there is a safety factor of two in this characteristic. The airplane analogy used previously shows the wisdom of this design. Having oversized kidneys allows for deterioration with age, the occasional intaking of a large number of toxins, and yet our design does not overtax us energy-wise because the size is limited. Those who choose to take toxins like alcohol into their systems would die instantly were this not the case. Each organ in our bodies is designed to give us maximum chance for survival in a constantly changing world. The degree of design and the flexibility involved challenges any explanation that depends upon chance and natural selection, and yet evolutionary change is what gives the biological systems their flexibility.
Not only are biological systems given an initial design that gives them optimum chance of survival in a harsh and constantly changing world, but they also have a design feature which allows changes in their makeup to adapt to the conditions in which they find themselves. We call this ability to change evolution--a word which can be used factually as we are doing here or theoretically as is done with Neo-Darwinism or punctuated equilibrium. Factually, we know that organs can be reduced in size and sometimes virtually eliminated if the environment they are in makes the organs unnecessary. I have seen fish and other animals in caves in southern Indiana that do not have functional eyes. There are birds living on islands where there are no predators that have lost their wings and muscle development that allowed them to fly. Even human beings have shown this ability to change. As children, all humans have a milk-digesting enzyme called lactase in their digestive system. As children become adults in most parts of the world, they lose the ability to develop lactase, but as adults they do not depend on milk for food anyway so it is no problem. Northern Europeans, however, do not lose the ability to retain lactase and thus are able to continue to use milk as a major food source. We can argue about whether this change is designed or the product of natural selection, but the point is that as food supplies change, even human beings have an over-all design that allows maximum utilization of the food resources available on the earth.
It is easy to look at a physical problem in a human being like a back problem and blame the difficulty on poor design or on the assertion that man's problems are all throwbacks to when mankind was a more primitive animal. The fact is, however, that when you try to make an improvement on the design of the human body, you find you cannot do it. Horizontal posture poses its own set of engineering problems which require special design techniques. The safety factors built into our bodies are optimal factors, and the ability to change adds flexibility to the design. We are not over-engineered nor are we under-evolved. We are "fearfully and wonderfully made" (Psalm 139:14).
(Scientific data for this article taken from "Best Size and Number of Human Body Parts," by Jared Diamond, Natural History, June, 1994, pages 78-81.)