7 ms·

Did Neurons Evolve Twice?

75 points by digital55 12y ago

sago 12y ago
Ugh, I hate reporting about evolutionary biology. This isn't an egregious example, but the 'it challenges the idea that complexity increases over time', 'it calls into question the origin of the brain', 'forces scientists to question how animals got their start', 'evolution debate', etc, gives me the creeps. In a country where more than 50% of the population thinks that evolution is bullshit, it doesn't help to try to phrase scientific disagreements to make it sound like it is some fundamental problem being argued about, instead of the placement of one phylogenetic branch. Now, the science itself is interesting. The DNA sequencing is quite weak evidence, from what I can see (its been 20 years since I did my PhD, though), but the radical difference in biochemistry is a good sign that, if they didn't evolve twice from scratch, at least the common ancestor probably used the cells that later became neurons in a fundamentally different way.
- Jedd 12y ago
  My initial reaction too - though the phrase that triggered it for me was 'challenges the deeply entrenched idea that evolution progresses steadily forward'. I am clueless about the identity of the demographic that holds this deeply entrenched idea, other than the vaguely labelled 'breathtakingly bewildered'. When you say 'in a country where more than 50%' ... are you referring to the country that you're currently in, or the one I'm in, or the one where you assume most people who are reading this article are in, by the way?
  - Elrac 12y ago
    He's most likely referring to the US. Depending on who does the polling and how, about half the population thinks the Theory of Evolution is a bad joke or a scientific conspiracy or something. The opposing side is known as "Creationists." They like to characterize scientifically informed people as "Evolutionists" but of course that's more misinformation. One of the various tracks of Creationist argumentation is that scientists make the "unjustified assumption that change progresses at a more-or-less constant rate" or, "that the rate of change today is the same as the rate of change way back when." They like to claim we can't know the decay rate of radioactive carbon (carbon dating, y'know) was the same a few thousand years ago (when the Earth was created) as it is today. I mention all this because this red herring about steady evolutionary progress is one of the arguments of Creationists, and so it's annoying to see those words used in that context in a science-y article.
  - dbbolton 12y ago
    > 'challenges the deeply entrenched idea that evolution progresses steadily forward' My inner devil's advocate wants to say that the writer meant that that idea is deeply entrenched in the general public's view of evolution, but that is very difficult to argue given the tone of the rest of the article. Back in my undergrad days (at a small state university), during one of the very first lectures in Biology, the professor really hammered the idea that evolution is not worse -> better or simple -> complex, but rather is governed by fitness, which constantly changes with the environment (so what's really awesome and complex might wind up being very maladaptive when circumstances change). She also made the point, through several counterexamples, that humans are not the pinnacle of evolution, which strangely seemed to offend some students. At any rate, I kind of assumed that this was standard knowledge in the scientific community if it was being taught in freshman Bio at my modest school.
storgendibal 12y ago
So if neurons did evolve twice, it is unlikely they are the Great Filter. Hopefully it is still behind us.
- melloclello 12y ago
  I had never considered that we might actually be ahead of the Great Filter. From what I'd read about it I've always thought of it as something we are yet to run into.
  - DiabloD3 12y ago
    There are multiple stages to the Great Filter. We have done everything but the last one: galactic colonization.
    - personjerry 12y ago
      This is a grand argument. Can you explain your reasoning?
      - DiabloD3 12y ago
        Wikipedia seems to explain it pretty well: http://en.wikipedia.org/wiki/Great_Filter#The_Great_Filter http://en.wikipedia.org/wiki/Great_Filter#The_Great_Filter
- Udo 12y ago
  Don't believe people when they say rubbish like this: Because they are so complicated, they are unlikely to have evolved twice. It's not like that complexity has spontaneously come into existence, it's the result of normal evolutionary processes which give rise to complexity of all sorts all the time. If you ask biologists about this, most would agree there is nothing inherently improbable about the evolution of any known cell type. Of course that doesn't mean those processes wouldn't produce a completely different organism on another world, but chances are this organism would have to solve similar problems as the ones here on Earth. The need to process information and react to it in some way is not unique to our world in any way. > So if neurons did evolve twice Looking at all the systems organisms are using to carry information (not just neurons, but all kinds of chemical signaling) suggests that these systems perform a very basic and ubiquitous role in all ecosystems. Even if the assertion about neurons was true (which it most certainly isn't), claiming all of our biological information-passing systems as special and "unlikely to evolve twice" is stretching an implausible proposition even further. > it is unlikely they are the Great Filter It's unlikely anything within biology is the Great Filter, but the thing at the beginning of biology might be a candidate: it's unclear how probable the formation of a simple cell from non-biological material is. My personal hunch is that the Great Filter might really be a combination of factors, both local to us and global, and abiogenesis _might_ be one of those that globally lower the odds for life significantly.
hayd 12y ago
> Because they are so complicated, they are unlikely to have evolved twice. I don't get this argument at all. It seems obvious that most of the time an organism gains a property it immediately dies (or fails to pass it to its offspring). They have lots of tries, they're not special. So: "Common ancestor" my arse. They insist on drawing these diagrams as trees when they are much more complicated graphs.
- Florin_Andrei 12y ago
  Anything that is unlikely to have evolved twice would be an automatic huge roadblock for evolution. If neurons really only did evolve once, and if that could really only happen this way, then complex life is basically a gigantic freak of nature and statistics.
- happimess 12y ago
  I think that you misunderstand what the article means by "evolved twice." Neurons certainly did not appear out of whole cloth in one generation, and the process involved many false starts and dead ends. The question is, do all currently living creatures with neurons trace back to a common ancestor who also had neurons, or are there several neuron-having lineages alive today, each of which traces back to a different earliest-neuron-having ancestor. In the latter case, each of those neuron-having ancestors would have shared a common ancestor, but one that did not have neurons. The lineage of all life on earth certainly creates a more complicated graph than a tree, but at the time scale needed to create a novel feature like neurons, it certainly looks like a tree. To say otherwise, you'd have to point to a case where genetic information passed laterally between species, rather than vertically from parent to child. This probably has happened [1], but is not so common as to make all tree-shaped charts misleading. [1]http://en.wikipedia.org/wiki/Symbiogenesis http://en.wikipedia.org/wiki/Symbiogenesis
  - im2w1l 12y ago
    >point to a case where genetic information passed laterally between species http://en.wikipedia.org/wiki/Horizontal_gene_transfer http://en.wikipedia.org/wiki/Horizontal_gene_transfer
raverbashing 12y ago
Wings are complicated and they evolved multiple times (insects, birds, bats) Neurons (or at least proto-neurons) are not extremely complicated, at least simple enough so that they can "do something" and then evolve. (Not sure how/if they were able to evolve without anything to control like muscles or at least some motor mechanism, but even bacteria does that)
- jug 12y ago
  Eyes (complex, image forming ones) are also believed to have evolved independently. Nature got it more right with the squids -- their eyes got wired so they lack a blind spot! Actually there are many cases: http://en.wikipedia.org/wiki/Convergent_evolution http://en.wikipedia.org/wiki/Convergent_evolution
infinity 12y ago
Because they are so complicated, they are unlikely to have evolved twice. This reminds me of the beginning of the babel fish argument for the non-existence of god by Douglas Adams: Now it is such a bizarrely improbable coincidence that anything so mindbogglingly useful could have evolved purely by chance ...
koberstein 12y ago
Pretty sure everything has evolved infinitely.

75 points by digital55 12y ago

sago 12y ago

Ugh, I hate reporting about evolutionary biology. This isn't an egregious example, but the 'it challenges the idea that complexity increases over time', 'it calls into question the origin of the brain', 'forces scientists to question how animals got their start', 'evolution debate', etc, gives me the creeps. In a country where more than 50% of the population thinks that evolution is bullshit, it doesn't help to try to phrase scientific disagreements to make it sound like it is some fundamental problem being argued about, instead of the placement of one phylogenetic branch. Now, the science itself is interesting. The DNA sequencing is quite weak evidence, from what I can see (its been 20 years since I did my PhD, though), but the radical difference in biochemistry is a good sign that, if they didn't evolve twice from scratch, at least the common ancestor probably used the cells that later became neurons in a fundamentally different way.

Jedd 12y ago
My initial reaction too - though the phrase that triggered it for me was 'challenges the deeply entrenched idea that evolution progresses steadily forward'. I am clueless about the identity of the demographic that holds this deeply entrenched idea, other than the vaguely labelled 'breathtakingly bewildered'. When you say 'in a country where more than 50%' ... are you referring to the country that you're currently in, or the one I'm in, or the one where you assume most people who are reading this article are in, by the way?
- Elrac 12y ago
  He's most likely referring to the US. Depending on who does the polling and how, about half the population thinks the Theory of Evolution is a bad joke or a scientific conspiracy or something. The opposing side is known as "Creationists." They like to characterize scientifically informed people as "Evolutionists" but of course that's more misinformation. One of the various tracks of Creationist argumentation is that scientists make the "unjustified assumption that change progresses at a more-or-less constant rate" or, "that the rate of change today is the same as the rate of change way back when." They like to claim we can't know the decay rate of radioactive carbon (carbon dating, y'know) was the same a few thousand years ago (when the Earth was created) as it is today. I mention all this because this red herring about steady evolutionary progress is one of the arguments of Creationists, and so it's annoying to see those words used in that context in a science-y article.
- dbbolton 12y ago
  > 'challenges the deeply entrenched idea that evolution progresses steadily forward' My inner devil's advocate wants to say that the writer meant that that idea is deeply entrenched in the general public's view of evolution, but that is very difficult to argue given the tone of the rest of the article. Back in my undergrad days (at a small state university), during one of the very first lectures in Biology, the professor really hammered the idea that evolution is not worse -> better or simple -> complex, but rather is governed by fitness, which constantly changes with the environment (so what's really awesome and complex might wind up being very maladaptive when circumstances change). She also made the point, through several counterexamples, that humans are not the pinnacle of evolution, which strangely seemed to offend some students. At any rate, I kind of assumed that this was standard knowledge in the scientific community if it was being taught in freshman Bio at my modest school.

storgendibal 12y ago

So if neurons did evolve twice, it is unlikely they are the Great Filter. Hopefully it is still behind us.

melloclello 12y ago
I had never considered that we might actually be ahead of the Great Filter. From what I'd read about it I've always thought of it as something we are yet to run into.
- DiabloD3 12y ago
  There are multiple stages to the Great Filter. We have done everything but the last one: galactic colonization.
  - personjerry 12y ago
    This is a grand argument. Can you explain your reasoning?
    - DiabloD3 12y ago
      Wikipedia seems to explain it pretty well: http://en.wikipedia.org/wiki/Great_Filter#The_Great_Filter http://en.wikipedia.org/wiki/Great_Filter#The_Great_Filter
Udo 12y ago
Don't believe people when they say rubbish like this: Because they are so complicated, they are unlikely to have evolved twice. It's not like that complexity has spontaneously come into existence, it's the result of normal evolutionary processes which give rise to complexity of all sorts all the time. If you ask biologists about this, most would agree there is nothing inherently improbable about the evolution of any known cell type. Of course that doesn't mean those processes wouldn't produce a completely different organism on another world, but chances are this organism would have to solve similar problems as the ones here on Earth. The need to process information and react to it in some way is not unique to our world in any way. > So if neurons did evolve twice Looking at all the systems organisms are using to carry information (not just neurons, but all kinds of chemical signaling) suggests that these systems perform a very basic and ubiquitous role in all ecosystems. Even if the assertion about neurons was true (which it most certainly isn't), claiming all of our biological information-passing systems as special and "unlikely to evolve twice" is stretching an implausible proposition even further. > it is unlikely they are the Great Filter It's unlikely anything within biology is the Great Filter, but the thing at the beginning of biology might be a candidate: it's unclear how probable the formation of a simple cell from non-biological material is. My personal hunch is that the Great Filter might really be a combination of factors, both local to us and global, and abiogenesis _might_ be one of those that globally lower the odds for life significantly.

hayd 12y ago

> Because they are so complicated, they are unlikely to have evolved twice. I don't get this argument at all. It seems obvious that most of the time an organism gains a property it immediately dies (or fails to pass it to its offspring). They have lots of tries, they're not special. So: "Common ancestor" my arse. They insist on drawing these diagrams as trees when they are much more complicated graphs.

Florin_Andrei 12y ago
Anything that is unlikely to have evolved twice would be an automatic huge roadblock for evolution. If neurons really only did evolve once, and if that could really only happen this way, then complex life is basically a gigantic freak of nature and statistics.
happimess 12y ago
I think that you misunderstand what the article means by "evolved twice." Neurons certainly did not appear out of whole cloth in one generation, and the process involved many false starts and dead ends. The question is, do all currently living creatures with neurons trace back to a common ancestor who also had neurons, or are there several neuron-having lineages alive today, each of which traces back to a different earliest-neuron-having ancestor. In the latter case, each of those neuron-having ancestors would have shared a common ancestor, but one that did not have neurons. The lineage of all life on earth certainly creates a more complicated graph than a tree, but at the time scale needed to create a novel feature like neurons, it certainly looks like a tree. To say otherwise, you'd have to point to a case where genetic information passed laterally between species, rather than vertically from parent to child. This probably has happened [1], but is not so common as to make all tree-shaped charts misleading. [1]http://en.wikipedia.org/wiki/Symbiogenesis http://en.wikipedia.org/wiki/Symbiogenesis
- im2w1l 12y ago
  >point to a case where genetic information passed laterally between species http://en.wikipedia.org/wiki/Horizontal_gene_transfer http://en.wikipedia.org/wiki/Horizontal_gene_transfer

raverbashing 12y ago

Wings are complicated and they evolved multiple times (insects, birds, bats) Neurons (or at least proto-neurons) are not extremely complicated, at least simple enough so that they can "do something" and then evolve. (Not sure how/if they were able to evolve without anything to control like muscles or at least some motor mechanism, but even bacteria does that)

jug 12y ago
Eyes (complex, image forming ones) are also believed to have evolved independently. Nature got it more right with the squids -- their eyes got wired so they lack a blind spot! Actually there are many cases: http://en.wikipedia.org/wiki/Convergent_evolution http://en.wikipedia.org/wiki/Convergent_evolution

infinity 12y ago

Because they are so complicated, they are unlikely to have evolved twice. This reminds me of the beginning of the babel fish argument for the non-existence of god by Douglas Adams: Now it is such a bizarrely improbable coincidence that anything so mindbogglingly useful could have evolved purely by chance ...

koberstein 12y ago

Pretty sure everything has evolved infinitely.