Evolution of Functional Disorders

Merriam-Webster’s Online Dictionary defines a Functional Disorder as, “affecting physiological or psychological functions but not organic structure.” These disorders are wide in the scope of body systems, and are characterized by the presence of symptoms and without the presense of a known physiopathology.

Disorders

Chronic Fatigue Syndrome
Functional Gastrointestinal Disorders
Functional Urinary Disorders
Fibromyalgia Rhematica
Female Sexual Dysfunction
Migraine
Respiratory Functional Disorders

Evolutionary Theory and Sympathetic Hypersensitivity
The Fight-or-flight_responseis the mechanism responsible for making early human ancestors capable of taking on a foe or fleeing from danger. While useful in the hunt or in battle, this mechanism is not limited in response to discrete instances of stress. Perceived stresses function to signal the given organism, in this case humans, to work to maintain a homeostatic balance (i.e. Gather food or water). However, this fine-tuned response passed down by human ancestors may not provide the same adaptive quality today. Changes in the nature of stress leave questions on how stress response affects the of humans. Individuals with lower stress threshold can then be subject to the detrimental effects of over-stimulation. Many of these effects have been documented, and while the true physiopathology of these “disorders of function” have yet to be determined, there is evidence linking these disorders to the over-stimulation of stress pathways.

The mechanisms behind the creation of a stress response can be responsible for deleterious effects to the body. When the body receives a stimuli that it perceives to be a danger, the locus ceruleus activates the sympathetic automated nervous system with the release of stress hormones epinephrine and cortisone. The subsequent response prepares the body to deal with the stressor. The body experiences an increase in heart rate, blood pressure, the dilation of the pupils, an increase in body temperature, muscle tension, and the suppression of the gastrointestinal system. Each of these responses gives an advantage which is expected to improve the individual's chances of survival. The dilation of the pupils allows for better sight, the increase in blood pressure increases the clarity of thought by providing more oxygen to the brain, and the suppression of the gastrointestinal system insures energy is used to overcome the stressor.

While most stress responses give the individual a selective advantage, some make no sense, as they do not give the individual an advantage. A classic example is goosebumps. The erector pilli muscles of the skin flex during an acute stress response resulting the raising of hair and the creation of goosebumps. This response gives the individual no selective advantage, it is simply a vestigial response used by hairier human ancestors to scare off predators. In the same way that this response has no selective advantage to humans, vestigial imperfections in stress response can have detrimental effect of the fitness of humans. This is due to the change of the nature of stress in the environment from physical to emotional. This change in the nature of stress in the present environment has led to the emergence on several stress related disorders which decrease the fitness of humans.

Increased levels of cortisone used in the creation of stress a response can lead to the atrophy of the hippocampus and the loss of memory . A study on rats indicated that prolonged elevations in cortisone resulted in the atrophy of the hippocampus. The study also indicated a strong correlation between the degree of cortisone elevation and the degree of atrophy over time. This study was done in comparison of a five year study on the rise of cortisone on the elderly, and their subsequent memory loss. This indicates that cortisone released in the stress response can cause memory loss. While this might only create a minor disadvantage for the individual, other effects which play a much greater role in terms of evolution.

Elevation in stress has also been found to affect the rate of infertility, miscarriage, late pregnancy complications, and impaired fetal development. The increase of cortisone suppresses the function of the pituitary female reproductive system. This is evidenced in Cushing's syndrome where increased levels of cortisone prevent the occurrence of pregnancy. Stress hormones also have their place in the timing of pregnancy, and increased levels prevent the proper timing (at 12 weeks cortisone levels approach those in Cushing's syndrome). High levels of cortisone also have a harmful effect on the uterus and the fetus and limit the secretion of lutenizing hormone (which trigger ovulation), ovarian estrogen, and progesterone (which has many functions in the establishment of pregnancy). This effect of stress has an incredible effect on evolution, as it directly effects the fitness of certain females. If, say, there would be any correlation between stress-induced infertility and another trait, it could be expected that with increased levels of stress in the environment, there could be a loss in genetic diversity.

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