Evolution of Depression

[athon]

What could be the evolutionary advantage of being able to suffer from depression? I'm not referring to clinical or severe depression, which would simply be an abnormal extension of 'normal' depression. I mean why would an organism feel a sense of loss or defeat to the extent that their normal behavioural functioning is impeded?

No reason why I'm pondering this. I feel great. But it just struck me today after considering past experiences with severe depression that I couldn't think of a reason why we could suffer from it.

Athon

 

[Dancing David]

Functional impairment is part of depression, severe as it were.

Moods are part of the human physiology and they serve some adaptive function, most likely.

But there need not be an evolutionary adavantage to depression per se, if it is associateed with traits that are advantageous then they will provide advantage and be passed on.

 

[Dr Adequate]

You might as well ask what purpose diabetes serves.

 

[writerdd]

If you're talking about depression as a disease, I agree it has no survival advantage, just as other diseases.

However if you're talking about sadness, it seems like it would work toward preventing an organism from repeating behavior that had negative results in the past.

 

[Paul C. Anagnostopoulos]

I think writerdd's got it. Now imagine what happens when the sadness circuit goes haywire. No evolutionary advantage, just haywireness, as with diabetes.

Although keep in mind tricks like that of sickle cell anemia, which confers some protection against malaria.

~~ Paul

 

[Melendwyr]

Even assuming that depression is a pathological state, it's entirely possible that it's just a side-effect of being able to feel sad. Exultation might not have a purpose, but if people can feel great, sometimes they'll feel really great. Same deal.

 

[Boo]

I think the term depression gets misused. Depression as an illness is extreme sadness, one that does not go away on its own.

Sadness is an emotional response to an event. When sadness gets out of control then there is depression.

Sadness would seem to serve a purpose as a cause to achieve an effect such as emotional bonding.

I think this can probably be said of all emotions. If the affect is completely flat then there is no effective way to emphasize our reaction to an event.


This is just pure speculation on my part.



Boo

 

[ChristineR]

You're all wrong. As a person who suffers from severe depression, I can tell you that it has a distinct evolutionary advantage.

Depression differs fundamentally from sadness. Sadness is a temporary state in reaction to events. Depression is a long lived state in reaction to a series of events.

Most of you have probably heard about Seligman's learned helplessness experiments where Seligman shocked dogs until they curled up in a corner and whined. The dogs remained depressed even after Seligman stopped shocking them, and even had a hard time learning that they could control the shocks when they were allowed to do so.

When exposed to painful stimuli, the body undergoes a whole bunch of physiological processes designed to help us cope with the crisis. In the long term, these processes (increased blood pressure, heart rate, adrenaline flow, etc.) are harmful. If a person is repeatedly exposed to painful stimuli which cannot be dealt with, the reactions can become more harmful than the original pain.

Depression is a state of reduced responsiveness associated with reduced neurotransmitters and reduced brain activity. The depressed person is less responsive to external stimuli, including pain, and less able to enter the agitated states which waste energy and resources on a hopeless cause.

The immediate problem with depression is that if and when the situation becomes less hopeless, the depressed person is less able to take the drastic action that may be needed to cope. This causes a vicious spiral, where the situation can become worse and worse, reinforcing the depressive state until a person becomes dead--literally or figuratively.

 

[Melendwyr]

We might as well ask what the evolutionary purpose of grief is. There are those who think grief should be medicalized, since there are various 'treatment options' (read: drugs) that can reduce its extent and severity significantly.

Regarding the reduced neurotransmitter levels alleged so frequently: how exactly do you determine that the reduction in neurotransmitter release is not in fact the result of reduced activity in the brain centers that most heavily utilize those chemicals?

 

[kittynh]

We also have to look at people that have suffered from depression. While it isn't good for THEM, it may be some sort of thing that comes with their way their brain works.

I've known a lot of depressed people that simply haven't had much at all set them off.

Winston Churchill had it bad at times. Certainly set backs in his life often triggered them, but not all his episodes.

I've known a lot of artists that drank, mainly to deal with their depression. Their need to be left alone, and indeed thier rejection by people that might normally have sought them out, allowed them to make some great art. And so it has been with many writers and artists through history. Not so good for the artist or writer, good for the rest of us. Plus, there is major depression and then living with depression long term. An artist producing any kind of work is not in a major depression.

 

[Dogdoctor]

It is possible that there is no advantage in feeling depressed. However you might just think of it as the other side of the elated scale. ChristineR presents a possible scenario that it decreases activity in a hopeless situation. Kittynh presents another idea is that it gives motivation to do something else. It may be that in primitive times we would be too occupied with getting food and surviving the elements that we hardly had time to engage in the self pity accompanied by the typical modern depressed individual. So how things would work out would be different in that we would get over it quickly and perhaps use it to fuel a drive for more food, better living conditions. Another possible function is that in the case of groups of individuals the depressed person might be more willing to perform risky behavior to help the community.

 

[UrsulaV]

I'm not referring to clinical or severe depression, which would simply be an abnormal extension of 'normal' depression. I mean why would an organism feel a sense of loss or defeat to the extent that their normal behavioural functioning is impeded?

Well, as long as it doesn't actively stop you from reproducing, it wouldn't be selected against. And a sense of loss can be useful in social cohesion--if a wolf feels loss when its packmates leave or die, it's more likely to want to stick with the pack, and the pack offers a significant survival advantage. We may feel loss as an adaptation to keep us from wandering off from the group. And ultimately, that can get extended to all kinds of other things, sine that which does not make us sterile kicks around the DNA forever.

'Sides, if you mope into the cave and sigh heavily a lot, you may get pity sex, so for all I know, it's sometimes a reproductive advantage to feel a sense of loss.

 

[Dancing David]

Depression is a state of reduced responsiveness associated with reduced neurotransmitters and reduced brain activity. The depressed person is less responsive to external stimuli, including pain, and less able to enter the agitated states which waste energy and resources on a hopeless cause.

Brave words for someone who starts off with: You are all wrong.

There is a lot of depression that does not fit your definition and in fact your definition does not encompass the vast majority of depression.

I have agitated/anxious depression. I feel sad and overwhelmed quite frequently, untreated I can cycle through severe bouts of obsessive compulsions. All of which are treated quite well with an SSRI, I am less likely to be overwhelmed, have only reactive anxiety and sleep fairly well.

Your description of 'vegatative' depression applies to about twenty percent of people who would call themselves depressed or would meet the DSM-IV category of major Depression, the sysmtoms of lack of energy are not as common in depression as you seem convinced.

It is the traditional overview of depression but it is not the most common depressed state.

Depressed people are often overwhelmed, oversensitive and very reactive to pain, I don't suppose that you are aware of the use of ADs to treat pain, are you?

There are some doctors who feel that vegetative depression is in fact one of the indicators of bipolar disorder, when coupled with irritability, mood shifts and excessive energy at other times.

I don't often agree with Mel, but the lack of neurotransmitter is not usualy a culprit in depression, so I would be curious to see a citation for that, I haven't been readin research for three years so, it would be good to learn.

Point of fact depression is caused by over activity of certain areas of the brain.

 

[Dancing David]

If you want to look for adaptive benefits to depression then look to the circadian cycles. In higher latitudes it would be beneficial to sleep most of the winter and be more active most of the summer. Evolutionary biology might support that. And if you want to think that maybe depression is related to imagination and creativity, then that might be beneficial. Obsessice compulsive traits can be beneficial as can the extra energy of bipolar disorder.

 

[Skeptic Ginger]

There is a fallacy here in thinking only traits which provide superior survival advantages are selected. Darwin's survival of the fittest was generally true but grossly over simplified. The correct way of looking at evolution now is to discuss selection pressures.

There are 20-30,000 genes (don't want to look it up) in the human genome comprised of 3 billion nucleic acid base pairs. In addition to sheer volume, you need to consider there is a huge amount of variation in the population which is advantageous by itself. (The advantage is that when a new stressor is encountered, there is already a mutation in the population which can survive it.) Add to that the fact that many traits are piggybacked on to other traits so if one is selected, the other may be included by the nature of its relationship to the selected one. And we have two sets of every gene except the genes on the xy chromosomes that men have, while women have 2 of each including xx. So lots of genetic material isn't acted on one way or the other unless certain combinations of genes allow expression of them. And does evolution even act on traits which mostly manifest themselves after the normal child bearing years?

Then, add to all that complexity exactly what selection pressures are. They are not limited to the most fit. Malaria, for example, may select for sickle cell trait leaving the person debilitated in some other way. So while you are getting survival of the fittest, you have thousands of things competing to be the fitness thing that matters. In other words, what matters more, Malaria resistance or physical endurance? It isn't a simple formula.

And some selection pressures have nothing to do with survival. Many speculate that criteria for mate selection is based on things which imply the mate is fit. A preference for rosey cheeks or clear skin is supposed to be the result of those features being more likely in a more fit mate. However, some research does not support that hypothesis and it hasn't been confirmed. Male peacocks do not have a survival advantage with those big wasteful tail feathers that also make it hard to run from a prey. But the peahens love those feathers apparently and the bigger the display, the more popular the peacock.

Do you think attractive women make healthier mothers or do you think TV and other media role models influence how men decide what is attractive? Milk production isn't necessarily dependent on the size of one's breasts. Mine, if I may be so personal, are on the larger size yet I had very little milk when my son was an infant.

And I was in years past unfortunately, attracted to good looking men who were not necessarily the best providers. That was undoubtedly not the result of a perfect evolutionary process. It does, however, bring up another point. Evolution is very slow in slowly reproducing animals like humans. So environmental changes can get ahead of genetic selection. Maybe that hunk would have been a better choice 10,000 years ago. In this era I'd have been better off with a rich brainy type. Or maybe I am better off after all since I'm single now and don't really need a male's contribution to the household. It is hard to determine exactly which results are going to be more often selected in this very complex world.

Finally, you have to consider that while there may be the ideal genetic selection based on selection pressures, what we have in the end is that old bell curve. There are plenty of people who reproduce who aren't perfectly selected. It may be that depression doesn't interfere with reproduction in a big enough way to have been deselected. It is only present in a minority of humans after all.

 

[ChristineR]

Brave words for someone who starts off with: You are all wrong.

There is a lot of depression that does not fit your definition and in fact your definition does not encompass the vast majority of depression.

I have agitated/anxious depression. I feel sad and overwhelmed quite frequently, untreated I can cycle through severe bouts of obsessive compulsions. All of which are treated quite well with an SSRI, I am less likely to be overwhelmed, have only reactive anxiety and sleep fairly well.

The description I gave was very brief and far from technical, but I do not see these sorts of symptoms contradicting the basic claim, which is that depression arises as result of a coping mechanism which prevents the normal adaptions to stress from running out of control. Non-specific anxiety is traced to unsoluble problems--or if not to any real unsoluble problems, to an adaptive reaction to dealing with unsoluble problems.

Your description of 'vegatative' depression applies to about twenty percent of people who would call themselves depressed or would meet the DSM-IV category of major Depression, the sysmtoms of lack of energy are not as common in depression as you seem convinced.

It is the traditional overview of depression but it is not the most common depressed state.

Obviously depression covers a variety of symptoms. I did not mention lack of energy--I mentioned not expending energy on hopeless causes. There is a difference.

Depressed people are often overwhelmed, oversensitive and very reactive to pain, I don't suppose that you are aware of the use of ADs to treat pain, are you?

Of course I am. Quite a jump on your part.

There are some doctors who feel that vegetative depression is in fact one of the indicators of bipolar disorder, when coupled with irritability, mood shifts and excessive energy at other times.

Well if the vegetative depression shifts with the anxious depression, that's pretty much the definition of bipolar disorder. I doubt if you will find many doctors who will claim that all persons with vegetative depression are actually bipolar. Of course there's no hard line.

I don't often agree with Mel, but the lack of neurotransmitter is not usualy a culprit in depression, so I would be curious to see a citation for that, I haven't been readin research for three years so, it would be good to learn.

Point of fact depression is caused by over activity of certain areas of the brain.

For lack of neurotransmitters associated with depression, google "serotonin hypothesis" and "catecholamine hypothesis." Nothing that came up is really all that comprehensive. These are theories, not universally accepted.

The web is full of PET scans showing reduced brain activity in depressed persons. I am unaware of over-activity in the brain being associated with depression, but I don't doubt that there is some. A lack of one thing often indicates an excess of its antagonist. Could you specify what you meant?

Mel's question seemed rather odd to me. It's a chicken-and-egg thing. I'm not a neurologist, so I have no idea what mechanisims lead to the reduced neurotransmitter levels. Some advocates of the serotonin and catecholamine hypotheses would claim that the disruptions in neurotransmitter levels are the cause, some of their critics would claim that they are a symptom. I said nothing as to cause and effect, because I have no idea.

 

[writerdd]

>Evolution is very slow in slowly reproducing animals like humans. So >environmental changes can get ahead of genetic selection.

That statement doesn't make sense. Environmental changes are what drive selection and evolution. Or, from the reverse, individual fitness is determined by the environment.

Cultural changes, on the other hand, can get ahead of genetic evolution. But that is a unique situation, at least on this planet. Of course, since we are talking about depression in humans, culture may certainly come into play.

 

[Oolon Colluphid]

What could be the evolutionary advantage of being able to suffer from depression? I'm not referring to clinical or severe depression, which would simply be an abnormal extension of 'normal' depression. I mean why would an organism feel a sense of loss or defeat to the extent that their normal behavioural functioning is impeded?

No reason why I'm pondering this. I feel great. But it just struck me today after considering past experiences with severe depression that I couldn't think of a reason why we could suffer from it.

Athon

I think some people have wandered far from the OP.

FWIW, so long as normal activity isn't impeded for extended periods of time, then there is no actual disadvantage to feeling depressed due to loss or defeat. The real question as I see it is, why do animals even have emotions? How and why did they evolve? Are they an unavoidable consequence of higher functioning brain structure? Or are they merely an artefact of social conditioning? My guess is that it's all about chemicals, since moods can be ameliorated with drugs so easily. Now some will undoubtedly point out that such an approach is merely treating the symptom, not the disease. To that I would say, Athon's question was in regard to mild depression from completely normal and identifiable causes, not clinical depression, the cause/s of which are usually complex, irrational and self reinforcing. IMO, feeling 'blue' once in a while isn't necessarily a bad thing. It might not be pleasant to endure, but it makes feeling good feel all that much better. Life, to me at any rate, is all about contrasts.

 

[Roboramma]

Environmental changes are what drive selection and evolution. Or, from the reverse, individual fitness is determined by the environment.

Of course, but that doesn't mean that environmental changes can't occur before evolutionary change comes along to deal with them. In fact, almost by definition, they must. The environment changes, then the organisms evolve "in response".
There must be a time when the environment has changed, but selection hasn't had much of an effect yet on the organism. At least when we're talking about major changes.

For instance, the environment of the Kiwi-bird of New Zealand has changed radically with (among other things) the introduction of cats to it's environtment. But there hasn't been much evolutionary change that allows it to deal with that environmental change - one reason that it's in danger (well, I think it's in danger.)
If the Kiwi manages to survive, selection will probably act to adapt the decendants of the current population to their new environment. But it hasn't had time yet.

 

[Skeptic Ginger]

>Evolution is very slow in slowly reproducing animals like humans. So >environmental changes can get ahead of genetic selection.

That statement doesn't make sense. Environmental changes are what drive selection and evolution. Or, from the reverse, individual fitness is determined by the environment.

Cultural changes, on the other hand, can get ahead of genetic evolution. But that is a unique situation, at least on this planet. Of course, since we are talking about depression in humans, culture may certainly come into play.

I'll give you an example showing you have it backward.

When humans migrated north it took thousands of years for light skin to evolve. When light skin people migrate to Australia, they need hats and sunscreen to avoid a greater risk of skin cancers.

Hats are cultural, evolution is very slow in humans. It could just as easily be the environment that changes or the human changing environments.