Editor’s note: Physicians have a special place among the thinkers who have elaborated the argument for intelligent design. Perhaps that’s because, more than evolutionary biologists, they are familiar with the challenges of maintaining a functioning complex system, the human body. With that in mind, Evolution News is delighted to offer this series, “The Designed Body.” For the complete series, see here. Dr. Glicksman practices palliative medicine for a hospice organization.

Since the body is made from matter, it must follow the laws of nature that affect the atoms and molecules making up its trillions of cells. These laws tell us that heat is the transfer of energy from one object to another and temperature is a measure of the random motion within an object or its internal energy. The body’s core temperature is directly related to how much heat it produces from its metabolism, whether at complete rest or with activity, and how much heat it loses to or gains from its environment. The body must control its core temperature because, if it isn’t just right, it can adversely affect enzyme function, the integrity of the plasma membrane, and other cellular structures.

The body’s normal core temperature is set by the hypothalamus at 97^o-99^oF (36^o-37^oC). It receives data from the central thermoreceptors and keeps the core temperature at this set-point

using both voluntary and involuntary means. When your core temperature rises or falls outside the normal range, and you feel too hot or too cold, there are things you can do, like take off or put on warm clothes, to help bring the core temperature back towards normal. At the same time, the hypothalamus, using the sympathetic nerves, automatically sends out messages to the blood vessels and sweat glands in the skin to either promote or limit heat loss. Using both of these mechanisms, the body is usually able to keep its core temperature where it should be while staying active. Let’s look at what happens when the numbers dictating core temperature just aren’t right.

The commonest cause of an elevated core temperature is fever, also called pyrexia. Thistakes place when, under the influence of pyrogens, the hypothalamus increases the set-point. The body responds by reducing heat loss through the skin and increasing production through shivering to preserve this abnormally high temperature. That’s why you feel chilly and shake prior to developing a fever. Pyrogens are chemicals released by invading bacteria, immune cells involved in inflammation and fighting infection, and even some types of cancer cells.

Hyperthermia, another common cause of high core temperatures, is when the core temperature is above 99^oF (37.2^oC) despite having normal thermoregulatory mechanisms in place. This usually takes place when a person is working or playing hard, generating excessive amounts of heat within a hot and humid setting, and the mechanisms for thermoregulation become overwhelmed.

Whether due to a very high fever (hyperpyrexia) from illness or heat stroke from physical and environmental factors, a core temperature above 107^oF (42^oC), means that several life-threatening reactions are likely to take place. These include things like protein and enzyme breakdown, impairment of mitochondrial function, and loss of plasma membrane stabilization. All of this culminates in severe brain dysfunction, muscle breakdown, loss of thermoregulation, and multi-organ system failure, resulting in death.

Hypothermia exists when the body’s core temperature drops below 95^oF (35^oC) despite having normal thermoregulatory mechanisms in place. This usually happens when people are in a very cold environment without adequate protection. Hypothermia affects every tissue in the body by reducing cell metabolism and diminishing enzymatic activity, including the enzymes needed for energy production and usage. As the core temperature drops below 91^oF (33^oC), mental confusion is soon followed by loss of consciousness and thermoregulation itself.

Based on our knowledge of how the body works, the ability for our earliest ancestors to survive and reproduce depended on their ability to maintain the right core temperature no matter where they were or what they were doing. For if the system of control they used allowed the core temperature to drop below 91^oF (33^oC) or go above 107^oF (42^oC), they would have died. Real numbers have real consequences when it comes to dealing with the laws of nature. Not just any core temperature works for survival. It has to be the right one to preserve protein integrity and cell function in order to keep the brain and all the other organs and tissues in the body working properly.

Just because a system is irreducibly complex does not automatically mean that it will be able to function well enough to allow for life. Besides being irreducibly complex, systems that allow for life must also have natural survival capacity. By this I mean that each system must take into account the laws of nature. This involves having an inherent knowledge of what is needed to keep the organism alive and the ability to do what needs to be done.

The system that uses thyroid function and uses the sympathetic nervous system to adjust the blood vessels and sweat glands in the skin to keep the body’s core temperature between 97^o-99^oF (36^o-37^o C) seems to naturally know how to get the job done. The same can be said for each of the control systems discussed in this series that manage things like oxygen, carbon dioxide, hydrogen ion, hemoglobin, iron, water, sodium, potassium, glucose, respiratory and heart rate, and blood pressure. Not only do each of these systems demonstrate irreducible complexity with natural survival capacity, but the absence or serious dysfunction of any one of them results in death.

Given what you have learned so far about what it actually takes to keep you alive, are you, like Richard Dawkins, intellectually satisfied about the explanatory power of evolutionary biology?

The more you understand what it takes for life to survive within the laws of nature, the more you will come to realize how inadequate and overly simplistic the theories of evolutionary biologists. How cold-blooded animals evolved into warm-blooded ones is a case in point. That’s what we’ll consider next time.

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