The evolutionary advantage to depression (and sickness behavior) | Charles Raison
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Some scientists theorize that depression in humans may have evolved along with sickness. Sickness and depression share several symptoms in common, such as hyperthermia (elevations in body temperature). Physiological changes that occur during an illness, such as fever and ramping up of the immune system, are designed to be protective against pathogens. Dr. Raison asserts that in ancient times, physical trauma injuries were more apt to be lethal than in modern times. He hypothesizes that stress makes one more prone to suffer an injury and thus the immune system gets stimulated during times of stress. In this clip, Dr. Charles Raison describes how the body has evolved to employ some of the same physiological mechanisms in depression and physical illnesses.
- Rhonda: What would be the advantage to developing depression from an evolutionary standpoint?
- Charles: Well, the argument here is that depression, human depression, may have evolved out of sickness. And there’s actually a fair amount of evidence to suggest that that may be the case. So for one thing, if you make a list of the symptoms that you have when you’re acutely sick, and you cross those with the symptoms you have when you’re depressed, there’s a really significant overlap. Depressed people are a little more likely to wanna kill themselves, are a little more likely to have sort of beat down on themselves. That doesn’t happen as often in sickness, but many symptoms, and some very surprising ones, are shared by depression and sickness. The example I often given is hyperthermia, right? So, you know, when you’re really sick, when inflammation is activated, one of the things it does is induce a fever. We’ve known for many years that if you take medically healthy depressed people, they have chronic elevations in their body temperature. And it follows the same sort of diurnal pattern as you see in sickness. So you see more of this elevation at night. There’s some very interesting data actually done up the road in Los Angeles, at UCLA in the 90s, that if you measure core body temperature of people that are not depressed versus people that are, the depressed people’s body temperature is higher. Then if you treat them, in this case they used electroconvulsive therapy, which is, you know, very, very rapidly acting powerful treatment, you treat the depressed people, you measure the body temperature again, bang, it goes right down to the level of control people. So we’ve known for a long time that depression is a hyperthermic state, but, you know, if you look at the things that happen physiologically when you get sick, one of the things that happens is something called an “Acute Phase Reaction.” So you get a change in the chemicals that your liver makes, right? So you get a downgrading of sort of housekeeping chemicals like albumin, and you get an up rise in the things like CRP. You tend to also do things like lose iron, lose zinc, and you say, why, you know, when you get sick, why do you slump your iron? Well, the answer is because the microbes, especially intracellular bacteria, need the iron more than you do. They have to have that iron to replicate. You could live for a while without iron, but they can’t. And there’s all sorts of data showing that for instance, iron supplementation kills you if you’re infected, or kids are given iron in high pathogen third world areas are much more likely to die of infection. So, you know, what happens with evolution is you get a suite of reactions that although sometimes costly to the person, or to the person’s body, are generally more costly to the bacteria. So the reason that we get sick when inflammation gets activated is not just because nature wants to torture us, it’s because if you make a list of all the things that happen, many of them have been shown to be pathogen protective. So for instance, hyperthermia, fever is a powerful pathogen protector for a couple reasons. First off, it sort of ramps up immune functioning. But most microorganisms are not built to last, they’re built cheap, that’s why they can actually mutate so quickly. So they tend to unwind at higher temperatures. So, you know, a fever is an anti-pathogenesis, an antibiotic strategy, right? So it’s very striking that depression is so reliably associated with things like shunting your iron, or shunting your zinc, raising your body temperature, you know. So if you think about, you know, why would those characteristics occur in a condition like depression that we think of as being largely psychosocial, you know, if your girlfriend dumps you and you get depressed, it might make sense why you weep and cry. And, you know, maybe it be you sit down, and it makes you reevaluate your life, but why should it elevate your body temperature? Why should it cause your iron stores to be reduced? On the other hand, you know, if depression evolved out of sickness as a strategy for pathogen defense, all those things make a lot of sense. And so the argument is that if you look at the things that killed hominids and human beings before about 10,000 years ago, they were largely not the infectious agents that killed us across history, right? Most people died of things like malaria, and smallpox, and measles, these horrible crowd infections over the last 10,000 years since the invention of agriculture. Before that, most people died from trauma. It’s interesting, sometimes afflicted by other people just, you know, just get scraped, getting cut up. The things that kill you from trauma are much more likely to be extracellular bacterial things. Those are the types of organisms that are especially likely to be wiped out by the kind of sickness reactions that get activated both in depression and sickness. So we and others have made the argument that this is the way to think about it. That until modern times, stress was a reliable indicator that you were at significantly increased risk of wounding, and wounding is going to kill you because you’re going to get infection. So stress becomes linked with a pre potent inflammatory activation so that your immune system kind of run to their guard stations, it’s like smoke alarm principle, you know. Stress means you’re at an increased risk of dying from a wounding-based infection. So stress becomes reliably associated with inflammation. Inflammation induces sickness. But sickness and depression share a lot in common, so over time, what happens is that anything that signals a need for increased inflammation activates a suite of behaviors that in humans over time, also sort of evolves into depression. So it’s an even deeper way of saying that in fact, the link between inflammation and depression may be deeper across evolutionary time and for adaptive purposes, than it actually is in terms of mechanism.
The primary protein present in human blood plasma. Albumin binds water, minerals, fatty acids, hormones, bilirubin, and many drugs. Its main function is to regulate the oncotic pressure of blood, a form of osmotic pressure exerted by proteins that tends to pull water into the circulatory system.
A ring-shaped protein found in blood plasma. CRP levels rise in response to inflammation and infection or following a heart attack, surgery, or trauma. CRP is one of several proteins often referred to as acute phase reactants. Binding to phosphocholine expressed on the surface of dead or dying cells and some bacteria, CRP activates the complement system and promotes phagocytosis by macrophages, resulting in the clearance of apoptotic cells and bacteria. The high-sensitivity CRP test (hsCRP) measures very precise levels in the blood to identify low levels of inflammation associated with the risk of developing cardiovascular disease.
A mood disorder characterized by profound sadness, fatigue, altered sleep and appetite, as well as feelings of guilt or low self-worth. Depression is often accompanied by perturbations in metabolic, hormonal, and immune function. A critical element in the pathophysiology of depression is inflammation. As a result, elevated biomarkers of inflammation, including the proinflammatory cytokines interleukin-6 and tumor necrosis factor-alpha, are commonly observed in depressed people. Although selective serotonin reuptake inhibitors and cognitive behavioral therapy typically form the first line of treatment for people who have depression, several non-pharmacological adjunct therapies have demonstrated effectiveness in modulating depressive symptoms, including exercise, dietary modification (especially interventions that capitalize on circadian rhythms), meditation, sauna use, and light therapy, among others.
Animals characterized by higher activity during the day and sleeping more at night.
A critical element of the body’s immune response. Inflammation occurs when the body is exposed to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective response that involves immune cells, cell-signaling proteins, and pro-inflammatory factors. Acute inflammation occurs after minor injuries or infections and is characterized by local redness, swelling, or fever. Chronic inflammation occurs on the cellular level in response to toxins or other stressors and is often “invisible.” It plays a key role in the development of many chronic diseases, including cancer, cardiovascular disease, and diabetes.
In general, anything that can produce disease. Typically, the term is used to describe an infectious agent such as a virus, bacterium, prion, fungus, or other microorganism.
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