If you ask my friends: you are depressed it? I estimated to be a lot of people get a definite answer. Depression is so common that researchers estimate at least 30-50% of the people in their life a certain period of time has reached major depressive disorder (MDD) diagnostic criteria. Depressed people may be in a bad mood, depressed, unable to focus on the right thing, not the food or the experience of sexual pleasure, and even choose to end their lives. These are significant survival disadvantage. According to the theory of natural selection, depression gene - let us use this word the time being - should have been eliminated, why depression is still so common it?
We know the aging process also showed survival of many disadvantages, such as physical decline, decreased resistance to disease, memory loss and so on. If the depression in the elderly may be more common as a kind of aging-related diseases, without much thought to the significance of the evolutionary aspect. However, depression in young people and a lot of teenagers and young people even more. This is clearly not the aging can be explained.
It would not be suited to the human society is changing so fast it caused too violent? In this respect there is a typical example of this is obesity. Obesity increases the risk of many diseases, why life is still a lot of fat it? This is because in the long evolution we have been hungry hungry worries, without danger of fullness. We have enough food and there is fried chicken, french fries, cola and other days too short, natural selection has not had time to work. With this hypothesis to explain the depression has a certain rationality. In recent years, depression does have a growing trend. In the treatment of depression it is also called "into the chemotherapy," is to give a similar human ancestors as primitive life. (We can easily understand idyllic life or sunny beaches of Eden makes mood changed for the better, but sooner or later have to return to it in order to survive the pressure, fast-paced modern life. Of course herein, this is not to discuss effective treatment sex, mentioned only in passing), but this hypothesis is also obvious flaw: depression is not only a modern society only, but in the variety, or advanced or backward culture. Furthermore, depression and anxiety phenomenon is ubiquitous in mammals, other mammals other than humans apparently did not live a modern life.
When we deny these above explanation, it means that we recognize depression meaningful evolutionary. So what is so depressed in evolution were retained it? People have put forward a variety of hypotheses.
We know that pain is useful to our survival, but not all pain is beneficial. Some persistent chronic pain does not help us avoiding disadvantages, but in vain increase the pain. Mental anguish and physical pain on some similarities. Negative emotions such as anxiety, fear, and so allow us to focus on the problems encountered, to find solutions and avoid similar dangers in the future. However, the same as physical pain, mental anguish is not the only benefit their excessive and uncontrolled depression may lead to harm. But as long as the overall benefits outweigh its disadvantages can win in natural selection. Obviously, natural selection does not care whether animals happy, if the advantages outweigh the hardship sent optimist, then human nature will inevitably be less sun.
Depression may also help the body fight the infection. In many studies, we found a series of genes related to depression and immune simultaneously. Depression sedentary animals, energy can be saved against not very sociable, avoid infect each other.
People easily depressed when unable to extricate themselves immersed in a question, the depth of thinking that helps solve the problem over and over again. In the face of difficulties, depression is often advantageous for problem solving. In intelligence tests showed depression are more likely to get a high score. The brain 5HT (5- HT, serotonin) 1A receptor are targets of some antidepressants. Lack this receptor rodent face less pressure manifested depression. 5HT1A receptor is highly conserved among mammals, suggesting its importance. And this receptor in rats and enter a state similar to the depth of human thinking is a must. It seems to be a painful thought might increase our chances of success.
Some people believe that depression is a bargain (bargaining) between the individual and the family. A man of simple expression of pain, such as crying, complaining, perhaps not able to obtain the trust of loved ones, and long-term depression, then let loved ones seriously TA problems and meet the needs of TA. However, specific to a particular individual, in exchange for depression is sympathy or disgust in return I am afraid it is difficult to say.
Depressed individuals usually do not dare to take risks, it is easier to give up. This negative performance may certainly result in lost opportunities, but sometimes play the role of self-protection. For example, the group beat the boss, if you insist on a bar to play, you may be killed, but Gaqiweiba to "a man", there is no chance might come later. Popular point is Chengsi daring, starvation timid. Between the active and conservative require a trade-off. Some researchers found that when mice were undernourished easy in a state of depression or anxiety. Such mice tend to hide in a cave, rather than go out. Outings and mice hiding in the cave have advantages and disadvantages: outings have more chance of finding food and mates, while the risk of being eaten by predators is greater. In a typical three-species food chain (FIG), when more food is just few natural enemies, then go out activity is more cost- on the contrary, when food is scarce natural enemies more precisely, when not only is not easy to go out find food, but more likely to lose a life, so it is cost-effective shelter in a cave. Hungry mouse in the hole spin anxiety but do not dare to go out, which inadvertently increases the chance of their survival. Of course, if mice were smart enough to be settled risks and benefits, and to know how to take the initiative when many predators to hide, then they would not have to endure the pain of depression and anxiety. But this advanced mouse does not seem necessary, because they do not care about the pain or not the nature of it.
Guess you've seen, these hypotheses are more or less far-fetched, but also not very good compatibility with each other. Perhaps waiting for us on the molecular mechanisms of depression have more understanding to give a more reasonable explanation for it. For now, all we might say: This thing about depression is sometimes inevitable that some would have been the meaning of it.
(Author: intron)
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