Evolution of Depression

[Skeptic Ginger]

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".......

Another good example, an animal behavior change in response to an environmental change.

This reminded me to also point out that much of evolution occurs with the genetic variation already in place and selection pressures then act on those existing mutations. It still doesn't speed up the process since you need lots of generations for a variation to become more common. Unless you wipe out a large portion of the population leaving only those individuals with the mutations surviving to reproduce. Of course the slower the organism reproduces, it still takes time to repopulate.

For example, when you use antibiotics and leave the survivors with resistance behind, the whole colony becomes resistant as the survivors multiply.

After rabbits escaped and over ran Australia, a deadly rabbit virus was introduced to wipe them out. But, it left a few behind which repopulated the continent with resistant rabbits. Now the virus is just another endemic rabbit disease with a much lower mortality rate.

A few humans have some resistance to HIV. Interestingly, the mutation arose in a population not yet exposed to HIV. HIV may act as a selection pressure and increase the frequency of the mutation in the human population. The mutation doesn't offer complete resistance though, so it may only increase by a small amount.

So in these cases, the resistant mutation can arise after the selector or already be in the population in some members and increase after the selector.

 

[writerdd]

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.

I thougth that's what I said -- cultural changes are faster than evolutionary changes. I guess I wasn't clear in my wording.

However, I don't think your example is a good one because culture interferes with evolution (hats prevent some cancers, for example)... I have to think about the interaction with culture and evolution more. Since we humans manipulate our environments to a huge degree and since we create medicines and other things to help us survive where we would otherwise die, we seem to be circumventing evolution in a non-trival way.

In a non-human species, however, it seems to me that the rate of evolution in response to environmental change differs depending on how quickly the environmental change kills off the now unfit individuals and at what age.

It could happen in as fast as one generation if it were some disease, for example, that killed off all juveniles with a certain gene. It would take longer if it only killed off a few of the least fit individuals in any generation and left many more and less fit individuals live long enough to have offspring, such as cancer. A mutation that makes some individuals just a little stronger or faster would also take time to spread through the population, assuming that only the very slowest got eaten by predators, rather than a large percentage of the slower individuals.

So, it seems to me evolutionary change may be fast or slow, depending on the details.

 

[Avita]

The real question as I see it is, why do animals even have emotions?

Well, the partial answer to that would be - emotions help us make decisions. The emotions associated with similar decisions made in the past help us decide whether the newest decision is likely to be helpful or harmful to us. A quick search on PubMed brings up the following articles -

Role of regret in decision making

Damage to different brain structures which are responsible for emotional processing leads to different kinds of poor decisions - by extension from this study, people with regularly-functioning brain structures, which are the products of evolution, are capable of deliberating, rather than acting impulsively, and of weighing relative rewards.

Interesting study of how in situations that require risk-taking, it may actually be advantageous to have brain damage in regions which control emotional response. My impression is that most decisions made in life benefit from some level of caution, so outside of the experimental task, these subjects probably don't fare as well.

I'm too lazy at the moment to look for more, but if I may be permitted to simplify these findings to the utmost - what we normally call positive and negative emotions are more like signals. Broadly, positive = go ahead, get more of that, and negative = wait, there's danger there, avoid. Different emotions would signify different kinds of approach or avoidance. For example, ordinary sadness might signal merely "I don't like this situation and need to be cautious, but don't need to expend that much effort to avoid it," while severe depression might signal "I am in a hopeless situation, where there's no sense expending any effort at all, so I need to shut myself off and conserve my energy until something changes." Since during life, a person is confronted with situations where the most advantageous thing for survival is to confront as well as those where the most advantageous thing is to retreat, it seems quite natural that we would have evolved a signaling system that was capable of handling both possibilities.

 

[jj]

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.

Depression as a means of surviving winter?

 

[athon]

Man, there's a lot to digest here. Some of the posts are really good, and have led me to thinking I understand it a lot better now. Others... well, I was going to post lengthy rebuttals, but there's a lot to say and I don't have the time at the moment to give it the full attention it deserves.

I was referring to 'common' or non-pathological depression for a reason; yes, things in nature can go wrong (such as diabetes, and a range of other psychological disorders). Yet I'd venture to say that nearly every individual on this planet is capable of feeling a range of described emotions we can describe under the heading of 'depression'. Severe or chronic depression (add me to the list of sufferers, folks) is indeed where the normal pathways go 'haywire'.

Thanks to OC for trying to get the thread back on track.

Skeptigirl, I'm going to have to read your thread properly, because there's a few things I disagree with at first glance.

Emotions - from the little I've read - seem to be linked in with social relations, which is why I'm starting to lean towards a thought that depression might be a way to force empathy with others in a social situation. I'm wondering, does anybody here know of non-social organisms that suffer from human-like depression?

Athon

 

[Dogdoctor]

I'm wondering, does anybody here know of non-social organisms that suffer from human-like depression?

I don't know of any. Superficially it seems difficult to determine in species other than humans if they are experiencing an emotion similar to human depression. If they were not social it would only make it more difficult. Not an educated answer I know ..sorry.
How do the members the discussion board respond to depression? I find that doing physical menial mindless labor is comforting as well as hiking or surfing. I also find my creative forces are greatest when I was depressed.

 

[athon]

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.

True. Traits dominant in a species increase for a number of reasons, not least because they promote relative fitness in a given environment (relative being the key word here), because they are linked to some degree to other selected traits, in moments of bottle-necking, where inadvertant selection takes place without regards for the nature of a phenotype.

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?

To respond to the first part of this paragraph, variation is indicative of a strong population for a number of reasons. One, it is an indication that a population has developed variation over time since the last bottle-necking event. Another is that substantial variation allows a larger percentage of a population to survive a selection event. So, that much is true; variation indicates a healthier population than one that is large with reduced variation (such as many current whale populations).

However, genetic combinations (called 'matrices') that are dominant in dispersed populations - such as the human species - tend to indicate strong selection pressures. It is indeed possible that it resulted from a bottle-necking event, I'm willing to concede, but I feel that it's unlikely.

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.

Fitness is always relative to the environment and its competitors, don't forget.

Could depression be an example of past fitness? Possibly, and if so, what are people's thoughts? Again, I'm trying to picture where it could offer some degree of benefit over its competitors.

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.

I read an interesting paper on challenges to sexual selection using game theory recently. Sorry, that was a digression, but it did remind me that linked traits that are apparently an impediment to fitness might actually provide benefits in themselves through social relations. I didn't like the author's arguments, but they did make me think.

I have strong doubts that depression is a linked trait, however.

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.

Fat distribution is linked in sexual selection, certainly. And while there is no direct benefit, again the 'display' purposes are social by nature.

As I've started wondering, depression might be linked with social behaviours.

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.

En contraire, it is a rather dominant behaviour. Remember, I'm not talking about clinical depression, which could be (and probably is) explained by what you're indicating.

Depression as a behaviour is extremely common. Have you never been depressed over an event in your life? Spent a few days after breaking up with a boyfriend not being able to eat, curled up in bed wondering when the pain would go away?

Athon

 

[articulett]

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.

I agree--if it doesn't kill you, (and on occasion it encourages you to seek the comfort of the opposite sex), then there isn't anything from an evolutionary perspective that would purge depression from the genome...even less so if the sex results in offspring or if the depression occurs beyond the age of primary fertility--

Evolution isn't really about human goals--just genes getting into the future. In fact, when an individual reaches an age that he or she might take resources that could be used to support more descendents, it may be "evolutionarily beneficial" for an organism to fade away and/or die.

Nature does not have human happiness (or any creature's "happiness") as it's goal.

 

[epepke]

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'm not sure about the evolution of depression. Bipolar, on the other hand...

There would be value in a hunter-gatherer band to have people who could run after an animal for two or three days without sleeping. Bipolars can do this. Depression is just the cost. When the protein from the animal has been brought back to the band, and everyone has enough to eat, sleeping for a couple of days would be OK.

Unipolar depression may be a spandrel of bipolar.

 

[Skeptic Ginger]

I thougth that's what I said -- cultural changes are faster than evolutionary changes. I guess I wasn't clear in my wording.

However, I don't think your example is a good one because culture interferes with evolution (hats prevent some cancers, for example)... I have to think about the interaction with culture and evolution more. Since we humans manipulate our environments to a huge degree and since we create medicines and other things to help us survive where we would otherwise die, we seem to be circumventing evolution in a non-trival way.

In a non-human species, however, it seems to me that the rate of evolution in response to environmental change differs depending on how quickly the environmental change kills off the now unfit individuals and at what age.

It could happen in as fast as one generation if it were some disease, for example, that killed off all juveniles with a certain gene. It would take longer if it only killed off a few of the least fit individuals in any generation and left many more and less fit individuals live long enough to have offspring, such as cancer. A mutation that makes some individuals just a little stronger or faster would also take time to spread through the population, assuming that only the very slowest got eaten by predators, rather than a large percentage of the slower individuals.

So, it seems to me evolutionary change may be fast or slow, depending on the details.

Evolution is very complex. A mutation which is fatal prior to childbearing age may still persist in a population for two reasons.

1) If it isn't expressed. We have two copies of everything (except genes on xy chromosomes in men) so defective genes are not always expressed.
2) If a mutation occurs easily, therefore continues to reoccur despite never reoccurring via reproduction.

You are correct that something which kills off all but a few members of a species can cause an evolutionary change as I also mentioned. But the speed of an evolutionary change still depends in general on how fast one reproduces the changed genetics.

Non-human species also interact with their environments. Humans are not the only animals that can make behavioral changes which counteract environmental changes. You only need look at city dwelling animals such as coyotes to see an example of that.

So to separate out human activities as interfering with evolution while ignoring the fact all organisms could potentially adapt to changes without genetic adjustments is really a false dichotomy. Humans are just able to adapt to differing environments to a greater degree than other species. Rats come a close second.

Being able to use science to adapt to differing environments is an evolutionary change in itself. While a diabetic may survive today, for example, they do so because of genetic advances in intelligence.

 

[Skeptic Ginger]

Depression as a means of surviving winter?

Not that it does, but one hypothesis could be depression is accompanied by slower metabolic rate, less activity, and so on. Less food would be required. Depression may just be an exaggeration or side effect of slowing down to conserve energy in the winter.

 

[aggle-rithm]

The first time I went to a doctor for depression, he asked if I suffered from frequent sadness, and seemed surprised when I said no. There was no sadness at all, just a general feeling of anxiety, negativity and hopelessness. To me, equating depression with sadness is ridiculous -- I would actually have to IMPROVE in order to feel sad.

 

[Skeptic Ginger]

Skeptigirl, I'm going to have to read your thread properly, because there's a few things I disagree with at first glance.

Emotions - from the little I've read - seem to be linked in with social relations, which is why I'm starting to lean towards a thought that depression might be a way to force empathy with others in a social situation. I'm wondering, does anybody here know of non-social organisms that suffer from human-like depression?

I don't read any substantial disagreements in your post that followed this one so I'm not clear on your specific objections. Perhaps you could simplify just the objections if I don't cover them below.

However, genetic combinations (called 'matrices') that are dominant in dispersed populations - such as the human species - tend to indicate strong selection pressures. It is indeed possible that it resulted from a bottle-necking event, I'm willing to concede, but I feel that it's unlikely.

In this case, those strong selection pressures on the matrix do not preclude positive and negative mix in that matrix. So I don't think we disagree here.

And I did not say the bottleneck (one did actually occur in the human population quite a while back) resulted in any specific genetic makeup in humans. I have no idea what changes that bottleneck resulted in. I assume an increase in intelligence but that is total speculation. It could just as well been the luck of the draw and humans in a particular location avoided the hazard, whatever it was.

As to the emotions and depression, I totally agree depression that wasn't pathologic could have evolved as part of the total picture of the advantages offered with group social interactions. So in addition to or in lieu of the slower winter metabolism I noted in my above post, this is also a good hypothesis.

Fitness is always relative to the environment and its competitors, don't forget.

Yes, and in addition, there may be more than one way to skin a cat. (That's an awful metaphor.) What I meant by the Malaria example was that the fit person could reproduce as well as the less physically fit person who escaped Malaria. Maybe one had more wealth and more wives but the other lived longer. These are of course exaggerated examples just for illustration.

I have strong doubts that depression is a linked trait..

I have no opinion, I merely wanted to expand on the possible mechanisms. You can't draw a good hypothesis if you don't know all the possibilities. After reading other's posts, the winter metabolism and the social interactions seemed to be the best hypotheses to me.

En contraire, [depression] is a rather dominant behaviour...

I was working under the assumption you were asking about pathological depression. It is now more clear you meant sadness and normal situational depression. The loss of a loved one is certainly depressing. That has to be something that evolved because we prefer the group. It's akin to physical pain. It tells you to avoid that situation. It would keep people in the group from leaving, and the other members comfort you if you are sad, as had been said.


As far as non-social animals suffering emotionally, how would we know? Is a hibernating bear sad? How do you measure that?

 

[Skeptic Ginger]

....Nature does not have human happiness (or any creature's "happiness") as it's goal.

Depends. If happy people are more inclined to reproduce it does. Happiness is an attractive quality in a mate.

But lest you feel the need to explain, I know what you meant.

 

[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.

and from another post

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

No jump at all, you stated quite clearly that a depressed person is less responsive to external stimuli, I am pointing out that this is not generaly the case, most depressed people are hypersensitive to stimuli.

So where was my jump?

 

[Dancing David]

The first time I went to a doctor for depression, he asked if I suffered from frequent sadness, and seemed surprised when I said no. There was no sadness at all, just a general feeling of anxiety, negativity and hopelessness. To me, equating depression with sadness is ridiculous -- I would actually have to IMPROVE in order to feel sad.

sad mood is one of the criteria that can be met for depression, but if you read Beck's Cognitive Theoryy of Depression he points out that the cognitive triad is more indicative of depression, it is comprised of :
1. negative world view
2. negative view of the future
3. negative view of the self.
Frozen feelings or lack of feeling is commonly reported in depression as is sad mood.

I usualy hace to ask about twenty questions to asses deprssion.

 

[Dancing David]

I'm not sure about the evolution of depression. Bipolar, on the other hand...

There would be value in a hunter-gatherer band to have people who could run after an animal for two or three days without sleeping. Bipolars can do this. Depression is just the cost. When the protein from the animal has been brought back to the band, and everyone has enough to eat, sleeping for a couple of days would be OK.

Unipolar depression may be a spandrel of bipolar.

The major mental illnesses tend to associate in families, schizophrenia, depressions, bipolar and anxiety. Some families have only one trait but others have all of them.

It seems that deprssion and anxioety usualy cluster but bipolar associates freely, especialy with alcohol addiction.

Given the way that the north american continent was settled I have wondered if that led to bipolar people leaving europe and moving to the US.

 

[ChristineR]

and from another post



No jump at all, you stated quite clearly that a depressed person is less responsive to external stimuli, I am pointing out that this is not generaly the case, most depressed people are hypersensitive to stimuli.

So where was my jump?

You implied that I had never heard of the use of anti-depressants as painkillers, and did so rather smugly at that. You seem to think that the fact that depression is often reduced response to external pain contradicts the use of anti-depressants as pain killers.

 

[Roboramma]

The first time I went to a doctor for depression, he asked if I suffered from frequent sadness, and seemed surprised when I said no. There was no sadness at all, just a general feeling of anxiety, negativity and hopelessness. To me, equating depression with sadness is ridiculous -- I would actually have to IMPROVE in order to feel sad.

Good point. You know, it might sound weird, but I often find myself feeling happy when I'm depressed. I'll find myself thinking, "Huh, that's weird. I've got this overwhelming feeling of happiness, yet I'm miserable."
It's a very strange sensation for me, when there's a feeling of hopelessness and despair at the same time as feeling completely content with how things are at the moment.

I think it's a combination of being happy with whatever I'm doing at the moment, but at the same time finding that in general I'm in some situation that I can't see a way out of, or facing a difficulty that I just really don't want to face, but can't see any way around, etc.

 

[Skeptic Ginger]

... You seem to think that the fact that depression is often reduced response to external pain contradicts the use of anti-depressants as pain killers.

Not to get involved in your discussion here since I haven't followed it, but I had a comment on this.

The idea of using anti-depressants for pain is not based on the drugs alleviating pain directly. Rather some people complain of chronic problems with few or no physical findings like fibromyalgia. Anti-depressants help, suggesting the disorder is a psychiatric rather than a physical problem.

If anyone wants to attack that premise please don't hijack the thread as it is a different subject.