Depression rates have been growing continuously every year. More and more of our loved ones are affected by this disease, and people are finding it increasingly difficult to cope with certain conditions of life at times. The question that many wonder is, what has caused depression to become so common? Theories vary between psychologists, neurobiologists and evolutionary biologists. This paper will examine the facts of depression, studies of depression, along with the reasons for depression, and the reasoning for its steady increase of victims, from an evolutionary perspective.

A depressive disorder is an illness that influences the body, thoughts, and mood. It affects how people eat, sleep, feel about themselves, and how they think about things. The symptoms of depression vary from case to case. Symptoms include feelings of hopelessness, pessimism, guilt, worthlessness, decreased energy, fatigue, loss of appetite or over eating, thoughts of death or suicide, restlessness, irritability, difficulty concentrating, remembering and making decisions. Those who are depressed lose interest in hobbies and activities that were once enjoyed, such as sex (National Institute, 2001, Depression).

Depression statistics that are available from past to current years do not correctly indicate real or actual numbers in the total population. This is because of misdiagnosis, which occurs between 30 and 50 percent of the time and because only half of all depression cases are actually documented. Available statistics are based on those cases in which patients seek care and/or are discovered to have the illness through surveys and studies ("Statistics," 2000). In 1998 depressive disorders concerned an estimated 9.5 percent of American adults ages eighteen and over, approximately 18.8 million people. In 2000, it was found that nearly twice as many women (12%), as men, (7%), have a depressive disorder each year (National Institute, 2000, The Invisible). Ten percent of Americans suffer from clinical depression (Goode, 2000). Twelve million women in the United States experience an episode of depression every year. Overall, one in every eight women develops depression at one time in their life ("Statistics," 2001). Depression is also becoming more common in adolescents and children. As many as 1 in every 33 children experience this invisible disease. Teenage girls are more likely to acquire depression than teenage boys (National Community, 1998,CMHS); one in eight adolescents may have depression (National Council, 2000, NIMH). Major depression is found to be most common in the mid to late twenties ("Statistics," 2001).

Neurobiologists and psychologists argue whether ego-detrimental experiences and self-depreciating thoughts or biological, and chemical processes are the causes of depression. Genetic researchers have put forth great effort in the past twenty years trying to recognize the genes that are linked to depression. So far, these genes have escaped discovery. This may be due to the fact that depression involves several genes, which form a small, hard to recognize combined effort. Serotonin, a neurotransmitter, has a large impact on depression. Depletion of this component might contribute to depression by affecting other kinds of neurons. Serotonin-producing cells branch off into many other regions of the brain that are thought to participate in causing depressive symptoms (Nemeroff, 1998). Evolutionary biologists believe that depression has evolved as a self-protection adaptation.
 

The above figure explains depression as the, F, signs and symptoms, occurring because of psychological or physiological events or both of which happen at E, psychological, physiological, or both. Dealings at E may be due to events occurring because of inclinations to depression related traits, A, B, or C. Explanations include genetically influenced trait features, C, such as neurochemical systems, and an assortment of possible B-C-D-E-F relations. Interactions between a normal genetic profile, A, and D, differences in being raised, or the current environment leading to E, psychical or psychological deficiencies and F, signs and symptoms of depression, are less frequent (McGuire and Troisi, 1998).

When looking at evolutionary models for depression it is important to keep in mind that they integrate-situation-influencing factors, and that already existing models are considered in rationalizing with these models. Keep in mind that there are no established definitions of mental conditions and evolutionary models suggest that certain typed and features of depression are objective (McGuire and Troisi, 1998).

Evolutionary biologists have theorized that depression is a self-defense mechanism. John Hartung, an evolutionary researcher of the state University of New York suggests a hypothesis different from those taking an evolutionary aspect. He suggests that depression is common among people whose abilities threaten those of their superiors. The best protection would then be to conceal abilities and deceive oneself about them so then to more willingly conceal your objectives. This would explain the cases of low self-esteem in very successful people (Nesse and Williams, 1999).

John Price, a British psychiatrist, views depression as a result of a situation where a person cannot win a hierarchy conflict and refuses to succumb to a more powerful person, position, or situation they cannot control (Nesse and Williams, 1999). Another researcher, Dr. Emmy Gut, of Sweden, wrote a book in 1989, "Productive and Unproductive Depression," in which she established that depression is a normal mechanism. It is an attempt toward adapting to a problem (Goode, 2000).

Recent researchers have concluded depression is a plea for help, a strategy into manipulating others to provide assets, a signal of submission and yielding in a conflict, or a means to preserve energy (Goode, 2000).

In Dr. Randolph Nesse and George C. Williams, PhD’s book, "Why We Get Sick: The New Science of Darwinian Medicine," they consider depression to be helpful for several reasons. Sadness will change one’s behavior, thereby stopping the current harmful activity or prevent future harmful activities. We can behave differently after a loss so then our future looks more positive in three steps. First, stop what you are doing; so then the damaging action is then stopped. Secondly, set aside the common human tendency of optimism. Studies have found that most people often overestimate their effectiveness and abilities. Finally, we can take off the "rose-colored glasses." Once this is done, then we can reasses our goals and strategies more objectively (Nesse and Williams, 1999).

These authors believe that "low mood" keeps us from jumping abruptly to escape momentary difficulties. As difficulties increase and energy is wasted, depression helps separate us from hopeless situations, so then we can consider alternatives. The capacity for high and low mood is a mechanism for adjusting the assigning of resources as a function of favoring current depression on the opportunities. If there is little hope for a rewarding payoff, it is best to just sit and wait rather than waste energy (1999).

Dr. Nesse, a director of the Evolution and Human Adaptation program at the University of Michigan’s Institute for Social research, has done some studies and has synthesized some arguments of his own. He maintains that some forms of depression result from genetics and brain abnormality. He also believes, however, that other cases may have their foundation in evolutionary history (Goode, 2000). Depression developed as a defense mechanism, a useful response to a situation in which a desired goal is unattainable. Depression may help a person disengage from what proves to be a hopeless effort. It is worthwhile to be depressed. Depression has low costs, when compared with its potential for protection. Nesse’s theories draw from Dr. Eric Klinger, a psychologist from the University of Minnesota, whose studies have shown that depression plays an important role in the process of separating from a goal or situation. The fact that depression sets in after someone suffers failure or a loss is significant. It slows you down, helps you to take a step back, consider the situation and approaches differently (Goode, 2000).

There are a few models of depression that emphasize ultimate causes. The first model, depression as an adaptation trait, involves information processing and signaling capacities that are understood to be functional and condition initiating. They are expected to fluctuate between females and males. In 1936, Lewis developed a theory explaining depression as a way to obtain assistance from others. Price (1967), and Sloman (1976), considered depression as a response to unendurable, low social status. Then in 1980, Engle found depression to be a way to preserve energy and fulfills its task as a homeostatic regulatory process. Emmy Gut in 1989 proposed that coping with depression results in being more psychologically healthy and more self-aware. This model builds on the proposal that depression is developed as a tactic to respond to an actual or prospective reducing of goal achievements (McGuire and Troisi, 1998).

Another model is the pleiotropy model of depression. Pleiotropy occurs when a gene or genes affect many different aspects of phenotypes. Pleioropy could explain why depression occurs in pre-menopausal women, during puberty, and early adulthood. Some non-evolutionary hypotheses can be collected with this model, like neurochemical dysfunctions and low self-esteem (1998).

A third model is the trait variation model of depression. This model assumes that cross-person differences in trait clusters, and they have a discrepancy within clusters trait features. This has an effect on the possibility of depression. The trait variation model requires evidence of either functional capacity limit or conditional exposure prior to provisional onset. Biomedical information about traits or genes increases the likelihood of depression; sub-optimal traits may be physical and sexual selection may also play a role (McGuire and Troisi, 2000).

The developmental disruption model of depression involves disrupted-maturation programs. These disruptions are caused by contrast in timing, intensity, and type. This model enforces the idea of infants having a normal genetic make-up for maturation program. When a program is interrupted, it leads to depression or susceptibility to depression. The theory of this model suggests that when a child grows up normally it is more vulnerable to depression because a disruption will come as an extreme shock. Natural selection did not favor self-sufficiency, and dependency in humans. Babies cling and depend on their mothers (2000). So genetics and traits in children to not be able to handle severe or depression situations are prevalent. This could be a factor is the cause of depression being prevalent more in children of today’s society, home lives and family situations are becoming worse.

The competitive-loss or a decline-in-social-status model deems that when a social status declines and there is a competitive loss, then the individuals are more likely to acquire depression. A failure-to-resolve-interpersonal-conflict model regards that interpersonal conflicts result in either a dominant or ritualized submissive response with the person whom the conflict is with, which manifests as depression. Losses are anticipated, real, or imagined, and a loss produces depression (2000).

If we disregard the idea of depression as an adapting effort we can identify the "core" features of depression and study these features impending changing abilities. For example, to go from psychological to physiological conditions, or vice versa. Look at ways in which depression signs, symptoms, and causes can be used to create new theories in reason for depression. Environmental possibilities, whether depressed or not, bring psychological and physiological factors to the situation. These influence person-environment interactions. "Core" approaches to this idea have advantages. One is that it lessens the need to explain diversity in clinical findings and assists the development of the unitary causal hypothesis. In short, take the clinical studies data; use more than one evolutionary concept to elucidate core features and individual differences (McGuire and Troisi, 1998).

Viewing depression as a unitary adaptive approach may serve the advantage of speculation but may also delay attempts to develop comprehensive evolutionary explanations as opposed to "core" justifications. People are goal-directed and their abilities to signal that they are depressed evolved in the same manner that their capabilities to notice danger and to take action did.

Ideals that conflict with evolutionary hypotheses are ideas that emphasize phenotypic flexibility, cross-person comparisons in adaptive capacities, and selection favoring development of psychological mechanisms or traits that mediate behaviors in response to the setting and situation.

The above graph shows how depressive symptoms are shown in the population, along with the severity of the episodes and symptoms. The less severe the indications, the more likely it is only a mood change and not a depressive episode. Depressive mood fluctuations are familiar in our population (World Health, 2001, figure 1.3).

Different types of depression may develop in reaction to different adaptation problems. An episode of depression associated with a loss of loved ones may differ than depression from a loss of resources. Sub-optimal conditions may play a role in the onset of depression and they may manipulate instant clinical manifestations in their course. Some traits may not be influenced during increasing severity. Even though some qualities are thought to be adaptive, they may in fact increase the chances of depression. Evolutionary systems that compete for recognition may explain much of the clinical "noise" of depression that is overlooked (2001).

Depression is not only becoming more of a prevalent problem, but it is becoming a worldwide difficulty. It is seemingly more frequent in children, adults, and adolescents. Major depression is the leading cause of disability in the U.S. and across the globe in this century (National Institute, 2001, The Invisible). Depression strikes about 121 million people worldwide (World Health, WHO/OMS, 2001). Nearly ten percent of young adults in the US have suffered an episode of serious depression. Rates have risen in the past decades, doubling about every ten years in industrialized countries. Studies of 39,000 people in nine different studies from five regions of the world found that young people in each country are more likely to experience depression than their elders would have at their age. Rates are rising in societies of a higher degree of economic development (Nesse and Williams, 1999).

The next question to consider is what has caused depression rates to rise so dramatically and why has this been recognized only recently? Nesse finds it ironic that the human race has created a society where we are not hungry nor are we dirty. We are warm and clean etc., and yet so many people are unhappy and miserable. Are there new aspects of our modern culture and environment that makes depression and suicide more apt to occur? There are higher standards set today than ever before. Our ancestors’ goals were to collect enough berries to feed the family and to reproduce. The objectives of today’s society are to look a supermodel, have and raise perfect children, and make millions of dollars (Goode, 2000). Factors that have been found to increase the chances of depression are obesity, divorce, children living at home, poor relationships, low economic status, demanding occupations, high populations of the surroundings, education level (college), and diseases and illnesses such as cancer (National Institute, 2001, The Invisible). Divorce rates are climbing, populations of areas are escalating, jobs are becoming more high stress, and as I can attest to by experience, a college education is certainly putting some strains on my life. As one may figure, an unfortunate family would view the struggle to support the family as disheartening. Poor relationships would generate uncared for, and unloved sad emotions in one. All of these issues are familiar in this day and age.

Another characteristic of today’s civilization is advertisement, television, and envy. TV and advertisement have created picture perfect, fantasy worlds we strive to achieve. We want to live a life similar to those that are depicted on television and we want to be as attractive as the supermodels who are most loved. Being that we cannot achieve these "unachievable" goals we become disappointed. Jealousy, the green-eyed monster appears, and we envy others. We can never be satisfied with what we have. When we strive to get the money that other have, to wear the clothes that are stylish, to be as gorgeous as models and others, we have low chances of doing this, and once let down, we are sad, frustrated, and depressed (Nesse and Williams, 1999).

Depression is a modern disease. As our country and our living styles become more demanding, more involved, requiring more money and, needing more time, our lives become pushed to the limits, as do our minds and emotions. As individuals we each seek our own ways of dealing with these situations and conditions. For some it is to disengage from the circumstances as a whole, just deny any relationship with it. For others it may be to manage it slowly, being stressed out, but handling it with grace. Some go into total separation from society. Along with these ways of coping with the current objectives in society, come resulting hindrances. Physical, mental, and emotional suffering all may come into play. Teenagers today most certainly have a much higher chance of experiencing depression, as standards are greater, and stressful factors are building up. Unless society finds a way to slow jobs and social demands down, it looks as if depression will continue to rise.

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Statistics. Retrieved November 8, 2001 from the World Wide Web: http://www-rohan.sdsu.edu/~highfill/Statistics.html/ Resource of NMHA MHIC: Depression in Women Factsheet- www.nmha.org

World Health Organization. (2000). WHO/OMS, 2000. Mental Health and Brain Disorders. Depression. Retrieved November 8, 2001 from the World Wide Web: http://www.who.int/mental_health/Topic_Depression/depression1.htm

World Health Organization. (2000). The World Health Report 2001. Mental Health: New Understanding, New Hope. Figure 1.3 The Continuum of depressive symptoms in the population. Retrieved November 8, 2001 from the World Wide Web: http://www.who.int/whr/2001/main/en/figures/figures1.3.htm