7 ms·

It is difficult to imagine a system of evolution where "useless" survives in successful iterations.

nextaccountic 5y ago
It depends on the cost of carrying vestigial stuff around vs the time required to make such changes (thousands of years? millions of years?) Sometimes organisms carry things not very useful anymore for a looong time.
epistasis 5y ago
Your point of view in evolution is called Adaptionism, but there are those who believe otherwise, and use the term "spandrel" to talk about the "useless" things that evolution carries along. https://en.m.wikipedia.org/wiki/Spandrel_(biology) https://en.m.wikipedia.org/wiki/Spandrel_(biology) Of course, something that is currently useless may become useful as the environment changes. Or it may not. Personally, I find a healthy sense of detachment from purpose, and certainly from any sort of teleology, is necessary to become philosophically consistent with the evidence from evolutionary biology.
- ConcernedCoder 5y ago
  Thanks for the rabbit hole ( I've never really studied evolution outside of CS applications ). Your point of view about detachment makes quite a bit of sense to me, and if the spandrel idea proves true I guess we (Homo sapiens) will just have to take it on the chin...
- elliekelly 5y ago
  This is quite interesting! Thanks for sharing! So might it be that a species, as a whole, benefits from carrying around a certain amount of “spandrels”? A genetic insurance policy of sorts to protect against/quickly adapt to unforeseen changes? Has there been any research into the prevalence (or absence) of spandrels in species that have gone extinct?
  - epistasis 5y ago
    I'm not sure if there's much research in evolution about species that have gone extinct versus extant species, or at least I haven't encountered it. The human genome carries around a massive amount of spandrels, in the form of what is called "selfish DNA." About 15% of the human genome consists of repeats of a single sequence: the Alu gene, which seems to primarily exist to replicate itself in the genome. This is part of a class of genes called transposable elements: https://en.m.wikipedia.org/wiki/Transposable_element https://en.m.wikipedia.org/wiki/Transposable_element And when discovered in corn, accounted for 85% of the genome. Barbara McClintock, their discoverer, hypothesized that they serve as a growth bed for evolution. And over the years it has indeed been found that individual transposable elements can serve as the seeds for new control sequences that coordinate when to turn genes on and off. The major forces of evolution in vertebrates are not big changes in proteins, but rather changes in when and how various proteins get activated, and transposable elements serve a big function in allowing that sort of evolutionary change in genomic sequences. Does most repetitive DNA in the genome seem to be useless, in that its deletion or replacement have little effect on the genome? Probably! But all that fluff also facilitates more easy rearrangement of the genome, because if every part of the genome was essential, randomly moving a chunk of DNA into a new spot would likely kill off some useful stuff. But if there's a bunch of stuff that is useless, randomly copying some stuff into a random spot is less likely to disrupt something. If the genome is a hard drive, there's no "free list" or file system for the genome, so random writes are less likely to be disastrous if there's nothing of importance on most of the drive. I used to get upset at the term "junk DNA" but I don't really care one way or the other now. One cell's junk is another's treasure.
    - elliekelly 5y ago
      I very much appreciate you taking the time elaborate! It’s quite interesting and now I have a new rabbit hole to explore :)
BurningFrog 5y ago
I find it difficult to imagine a system of evolution where useless code is reliably removed.
- baruch 5y ago
  Presumably there is a cost to carrying the DNA, if it gets removed by chance and the cost was high enough the useless part will disappear. That however hinges on the cost being high enough, if the cost is negligible then there is no real pressure either way.
  - dekhn 5y ago
    this cost of "DNA size" is a long and ongoing argument in biology with no clear answer. Here's the strongest straw man argument in favor of "there are large amounts of non-funcitonal DNA which has zero evolutionary cost": https://www.cell.com/current-biology/pdf/S0960-9822(12)01154-2.pdf https://www.cell.com/current-biology/pdf/S0960-9822(12)01154...
enkid 5y ago
Certainly there are thing that formerly had a use but are less useful now. I'd be careful calling something useless, but if there isn't an advantage to getting rid of a feature, I see no reason it would be gotten rid of.
roywiggins 5y ago
Evolution is not that ruthless. Useless but neutral traits can just stick around, if there's no selection pressure to get rid of them.

It depends on the cost of carrying vestigial stuff around vs the time required to make such changes (thousands of years? millions of years?) Sometimes organisms carry things not very useful anymore for a looong time.

epistasis 5y ago

Your point of view in evolution is called Adaptionism, but there are those who believe otherwise, and use the term "spandrel" to talk about the "useless" things that evolution carries along. https://en.m.wikipedia.org/wiki/Spandrel_(biology) https://en.m.wikipedia.org/wiki/Spandrel_(biology) Of course, something that is currently useless may become useful as the environment changes. Or it may not. Personally, I find a healthy sense of detachment from purpose, and certainly from any sort of teleology, is necessary to become philosophically consistent with the evidence from evolutionary biology.

ConcernedCoder 5y ago
Thanks for the rabbit hole ( I've never really studied evolution outside of CS applications ). Your point of view about detachment makes quite a bit of sense to me, and if the spandrel idea proves true I guess we (Homo sapiens) will just have to take it on the chin...
elliekelly 5y ago
This is quite interesting! Thanks for sharing! So might it be that a species, as a whole, benefits from carrying around a certain amount of “spandrels”? A genetic insurance policy of sorts to protect against/quickly adapt to unforeseen changes? Has there been any research into the prevalence (or absence) of spandrels in species that have gone extinct?
- epistasis 5y ago
  I'm not sure if there's much research in evolution about species that have gone extinct versus extant species, or at least I haven't encountered it. The human genome carries around a massive amount of spandrels, in the form of what is called "selfish DNA." About 15% of the human genome consists of repeats of a single sequence: the Alu gene, which seems to primarily exist to replicate itself in the genome. This is part of a class of genes called transposable elements: https://en.m.wikipedia.org/wiki/Transposable_element https://en.m.wikipedia.org/wiki/Transposable_element And when discovered in corn, accounted for 85% of the genome. Barbara McClintock, their discoverer, hypothesized that they serve as a growth bed for evolution. And over the years it has indeed been found that individual transposable elements can serve as the seeds for new control sequences that coordinate when to turn genes on and off. The major forces of evolution in vertebrates are not big changes in proteins, but rather changes in when and how various proteins get activated, and transposable elements serve a big function in allowing that sort of evolutionary change in genomic sequences. Does most repetitive DNA in the genome seem to be useless, in that its deletion or replacement have little effect on the genome? Probably! But all that fluff also facilitates more easy rearrangement of the genome, because if every part of the genome was essential, randomly moving a chunk of DNA into a new spot would likely kill off some useful stuff. But if there's a bunch of stuff that is useless, randomly copying some stuff into a random spot is less likely to disrupt something. If the genome is a hard drive, there's no "free list" or file system for the genome, so random writes are less likely to be disastrous if there's nothing of importance on most of the drive. I used to get upset at the term "junk DNA" but I don't really care one way or the other now. One cell's junk is another's treasure.
  - elliekelly 5y ago
    I very much appreciate you taking the time elaborate! It’s quite interesting and now I have a new rabbit hole to explore :)

BurningFrog 5y ago

I find it difficult to imagine a system of evolution where useless code is reliably removed.

baruch 5y ago
Presumably there is a cost to carrying the DNA, if it gets removed by chance and the cost was high enough the useless part will disappear. That however hinges on the cost being high enough, if the cost is negligible then there is no real pressure either way.
- dekhn 5y ago
  this cost of "DNA size" is a long and ongoing argument in biology with no clear answer. Here's the strongest straw man argument in favor of "there are large amounts of non-funcitonal DNA which has zero evolutionary cost": https://www.cell.com/current-biology/pdf/S0960-9822(12)01154-2.pdf https://www.cell.com/current-biology/pdf/S0960-9822(12)01154...

enkid 5y ago

Certainly there are thing that formerly had a use but are less useful now. I'd be careful calling something useless, but if there isn't an advantage to getting rid of a feature, I see no reason it would be gotten rid of.

roywiggins 5y ago

Evolution is not that ruthless. Useless but neutral traits can just stick around, if there's no selection pressure to get rid of them.