There is nothing about evolutionary theory that posits that all current biological structures/functions must have a evolutionary purpose.

Only the system as a whole must carry superior fitness, not each of its individual components. Given a sufficiently complex system, its rather expected that there will be negative, or even outright destructive functions that arise. You can certainly try to find a positive reason for why cancer, disease, death during conception, etc exist, but there is a much simpler explanation.

Depression in this view, isn't something outright that was adaptively constructed, but merely a side effect of how the mind works.

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bubblyworld 4 days ago | parent | next [-]

My understanding of the "modern" point of view is that selection acting at the level of the gene (not the organism or group) is sufficient as a theory. The Selfish Gene and The Extended Phenotype go into this stuff in a lot of detail.

Totally agree with your first sentence though. And even if there is a plausible adaptive function it may have only been adaptive in the past, or might be a side effect of some other adaptive function (see sickle cell anemia), or a host of other possibilities.

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BriggyDwiggs42 3 days ago | parent [-]

Why not the group?

	▲	bubblyworld 3 days ago \| parent \| next [-]
		Have a read about kin selection, for instance. There are lots of facts about e.g social insects (like the male/female/sterile ratio iirc) that were thought to only be explainable by group selection, but later were found to work out purely from considerations of gene selection. I'm just a layperson though, would highly recommend Dawkins writing on this stuff. It's much less polemic than his writing on religion, if that puts you off at all. I think the basic criticism of group selection is that at an individual level it can be beneficial to go against the group's goal, and you need to explain why that doesn't happen (even very small advantages are rapidly boosted by selection). This is one of the great puzzles of selection - how does cooperation evolve from selfish interests? The theory of group selection just asserts that it does, which is not very satisfactory.
	▲	strken 3 days ago \| parent \| prev \| next [-]
		There's behaviour at an individual/group level that is only explained by selection at a lower level. Consider the placenta releasing allocrine hormones during pregnancy while the mother's body increases insulin levels, or consider male lions killing off the cubs of defeated males.
	▲	melagonster 3 days ago \| parent \| prev [-]
		Group selection only works under some rare situations. Groups should rapidly build and disintegrate to make group selection work.

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mothballed 4 days ago | parent | prev | next [-]

I've often wondered if depression is exactly that, a system level optimization. Sometimes depression just happens, but sometimes it is triggered by low social status, realizing you've hurt someone in an unjustified or accidental way, having other mental illness, being seriously injured, or some other way that threatens the fitness of the overall group. Depression might be a (albeit flawed) system level way of reducing the amount of physical and social resources those people consume so that the non-depressed strata of society can better take them.

Note: this is a speculation, not assertions of fact

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andoando 4 days ago | parent | next [-]

I think its just a natural consequence of our mind working on a positive-negative reward system, which I think its critical to any intelligence. Being manically positive is just as detrimental as being chronically depressed.

Its entirely normal to be negative, or to ignore stimuli, or decide not to do things. In some situations, say if you were trapped in a cage your whole life, you'd agree it'd be entirely normal to be depressed. It would make no sense to waste energy running around hitting iron bars that won't break.

In this sense, depression is somewhat of a social construct. We determine someone is depressed because we believe their reaction to the environment to not be normal.

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Filligree 4 days ago | parent | prev | next [-]

You’re proposing group selection, which always never happens.

Evolution functions not at the level of groups, or even individuals, but genes inside of individuals.

Most of the time thinking of it as group selection at the genetic level (=individuals) does work, fortunately.

	▲	andoando 3 days ago \| parent \| next [-]
		It makes technical sense that if one individual helped for example to make the rest of the colony propgate 3x faster, it would be a collective reproductive advantage
	▲	mothballed 4 days ago \| parent \| prev [-]
		I believe it would also apply similarly under kin selection.

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OgsyedIE 4 days ago | parent | prev [-]

Such phenotypes would fail to reproduce, leading to the genes for those phenotypes dying out.

	▲	mothballed 4 days ago \| parent [-]
		If the genotype is mostly 'expressed' as depression in certain scenarios that allow your kin to reproduce better at the expense of you reproducing worse, that's not necessarily true. Imagine for a moment, a version of depression that appears after someone gets their reproductive member cut off (perhaps encounter an angry lion?), but they are still around to compete for food with the extended family's children.

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Consultant32452 4 days ago | parent | prev [-]

The rule of thumb is if something has a cost and persists over time it must have some benefit even if we don’t understand what that is. Otherwise, creatures not paying the cost will outcompete over time.

	▲	thfuran 4 days ago \| parent [-]
		Or it’s caused by the same thing as something that does have a benefit.