6 ms·

Why would an animal lose its brain?

74 points by breitling 11y ago

caf 11y ago
The alternative hypothesis - that the brain has independently evolved twice - is in my opinion even more interesting. If true, it would seem to have implications for estimates of how easy it is for life to evolve intelligence.
- netcan 11y ago
  Whatever the origin of the brain organ in evolution, There has certainly been a lot of novel inventions after that time. A lot of interesting "design" has happened for a long time after that invention, separated by divergence. Cephalopods are very distantly related to us. Our last common ancestor with cephalopods is also our last common ancestor with slugs and hookworms. Yet many species are obviously highly intelligent. Their intelligence seems to work very differently from vertebrate intelligence. So, it's interesting thing that some descendant species of whoever invented brains opted out. But either way some sort of convergence did happen. Maybe brains evolved twice. Maybe they evolved many times from a common primitive nerve bundle that performed a very different function. Maybe this happened in a tangle of back and forth. The aye-aye lemur and the striped possum both evolved a long bug catching finger. We know that it's convergent rather than common ancestry because (among lots of reasons, but this is a neat example) it's a different finger. But, they both had fingers to elongate in the first place. So, given the same machinery to evolve and the availability of similar ecological niches (no woodpeckers, lots of bugs) they came up with a smiler solution. We know that brains, and their components are very flexible even in a mature organism. So it makes sense that evolution is wild and creative, repurposing the tool constantly. I mean the diversity in sense perception in different animals seems like evidence of radically evolving brains over relatively short periods of time. Even entirely new senses (eg echolocation) seem to evolve fairly easily and quickly. TLDR: depending on what your precise definition of "brain" is, this seems very likely. Aye-ayes & striped possums both have elongated fingers that evolved separately from regular fingers. The fact the they both evolved from regular fingers is interesting, but neither here nor there for most interesting conclusions. Brains are probably like this, but way more interesting any mysterious. ^I feel like I have to credit Douglas Adams who wrote beautifully about these animals.
  - caf 11y ago
    So I was using "brain" in the same sense as the article, as a shorthand for "central nervous system". I think we already knew that once you acquire a CNS, it can evolve rather rapidly to quite complex brains, and that doesn't seem intuitively surprising. It's that first leap to a basic nervous system which seems like the high activation energy barrier, and if it may have happened twice rather than just the once, then I find that interesting.
    - netcan 11y ago
      The 'earliest known example' (520mya) discussed dates to around the cambrian explosion, the geological period where the fossil record is rich with "earliest examples" and type specimens for phylums. Maybe another way to put it is 'The definition of brain used in this article might apply to organs other than the brain in modern species." It's basically a nervous system, centralized or not. Who knows what it did or what it was for. It may have a predecessor outside the animal kingdom. Plants have sensory perception, or some version of it. I'm not disputing the claims in this article or anything else. I'm basically agreeing with you. Whether or not some nervous system, nerve cells or complexes of nerves evolved 520+mya and were 'lost' in some phyla or was evolved through convergent evolution a little later, it's partially a semantic issue: do we call something a brain. Most of what makes a brain a brain probably came later and evolved separately in different phyla. This means radically different ways of doing things. BTW, Richard Dawkins really turned me on to evolutionary biology (a side gig, when he's not arguing with dummies) in some of his books. "Ancestors Tale" is awesome for really getting the "phylogenetics" way of thinking discussed here.
  - a_bonobo 11y ago
    Interesting that you chose cephalopods - their eyes work similarly in the "basic layout" to vertebrate eyes but cephalopod eyes have a few key differences, which may again be convergent evolution, since the most recent common ancestor didn't have eyes, only a photosensitive spot (which is still present in jellyfish).
  - agumonkey 11y ago
    > Cephalopods are very distantly related to us. Our last common ancestor with cephalopods is also our last common ancestor with slugs and hookworms. Yet many species are obviously highly intelligent. Their intelligence seems to work very differently from vertebrate intelligence. Similarly old low bit-width CPUs are "as" potent as nowadays CPUs according to the work/dataflow they have to handle. Or even OSes, win95 could do a lot that a recent Linux/WM can do at a tiny fraction of the structural cost/complexity. Also text encodings.
spiritplumber 11y ago
For the same reason why, say, version 7 of the WRT-54G router had half the memory that version 2 had. It's expensive (money or calories) and the extra functionality doesn't help in getting more out there (selling or reproduction).
WalterBright 11y ago
Plants have also survived for hundreds of millions of years with no brains.
- deleted 11y ago
  [deleted]
- grondilu 11y ago
  Indeed. My memory is failing me but I seem to recall having heard or read someone talking about the brain and stating that its sole purpose is to move the body. Thus, an organism that does not move does not need a brain, and as a proof of this idea he mentioned that some animals, like some medusa, loose their brain once they fix themselves to the floor (turning into polyps in the case of medusa).
  - joeyo 11y ago
    Daniel Wolpert has a TED talk where he makes this point [1]. And I think he's basically got it right. Certainly there are organisms that can move without a nervous system (single celled amoebas, venus fly traps, etc) but by and large you need an (electrical) brain if you are going to react to something on a fast timescale. 1. http://www.ted.com/talks/daniel_wolpert_the_real_reason_for_brains http://www.ted.com/talks/daniel_wolpert_the_real_reason_for_...
  - smorrow 11y ago
    Well. To move the body to which your genitals are attached.
- netcan 11y ago
  Do we know that for sure?
holychiz 11y ago
what?! no joke about our bosses? oh right, you're all your own boss here. :)
beaner 11y ago
Another example of where more brains doesn't necessarily mean evolutionary advantage is modern humans. It can be seen all over the world that the less intelligent procreate more. The intro to Idiocracy makes the point well: https://www.youtube.com/watch?v=hL1-340ODCM https://www.youtube.com/watch?v=hL1-340ODCM It's kind of a joke, but also really not. It's frightening.
- MichaelGG 11y ago
  But that relies on smart people having figured stuff out to the point where it is no longer an advantage. If human intelligence declined to the point where we lost that kind of knowledge, then being smarter could probably become a benefit that's selected for. Rinse, repeat?
  - beaner 11y ago
    Yeah, we did have a dark ages that lasted for a thousand years. Nothing says the same thing can't happen again.
- givan 11y ago
  Why being poor or living outside western culture means less intelligent?
  - beaner 11y ago
    First, I never said anything about western culture. (Note that the example is inside America.) Second, the poor generally don't have the same access to good education so in general it is true. Third, I edited my comment because I know they're not equal and it was a mistake.
- vog 11y ago
  > It's kind of a joke, but also really not. It's frightening. It is a joke. Idiocracy relies on the assumption that the "more intelligent" people are snobs and too busy and too perfectionist with their life to have children, while the "less intelligent" people are mostly having sex and are too lazy to apply contraception properly. Essentially, the first half of the movie is a justification for elitism. I'm less afraid of Idiocracy to become true, but more afraid of politicians acting as if they believed in this movie. The second half of this movie is more interesting, though. It may be interpreted as an analogy of how the most gifted people (in the sense of "intellectual giftedness") may feel living in today's world. (by putting today's "normal" people into a dumb world) But even that is, of course, a funny hyperbole, and nothing to take too seriously.
edem 11y ago
So if someone does not use his brain for long he/she becomes demeted becuse he does not need a brain?
skywhopper 11y ago
Key point: evolution does not necessarily working towards more complexity or a specific endpoint. Rather, the unique selection pressures that exist when organisms attempt to reproduce vary, as do the particular genetic changes that happen due to any number of factors (mutation, viruses, gamma rays, copy errors, bacterial absorption, whatever). Each generation may face similar or different pressures. Certain mutations may be more or less likely. In some cases, the mutations that survive may be pure random chance. In others, only a specific mutation may have saved the organism's particular genes from extinction. The future organisms and genes that emerge from this chaotic process are unpredictable. Sometimes those organisms will lose features, sometimes gain, sometimes have weird changes that don't appear to make sense. All that matters is: do the organisms continue to reproduce successfully generation after generation?

74 points by breitling 11y ago

caf 11y ago

The alternative hypothesis - that the brain has independently evolved twice - is in my opinion even more interesting. If true, it would seem to have implications for estimates of how easy it is for life to evolve intelligence.

netcan 11y ago
Whatever the origin of the brain organ in evolution, There has certainly been a lot of novel inventions after that time. A lot of interesting "design" has happened for a long time after that invention, separated by divergence. Cephalopods are very distantly related to us. Our last common ancestor with cephalopods is also our last common ancestor with slugs and hookworms. Yet many species are obviously highly intelligent. Their intelligence seems to work very differently from vertebrate intelligence. So, it's interesting thing that some descendant species of whoever invented brains opted out. But either way some sort of convergence did happen. Maybe brains evolved twice. Maybe they evolved many times from a common primitive nerve bundle that performed a very different function. Maybe this happened in a tangle of back and forth. The aye-aye lemur and the striped possum both evolved a long bug catching finger. We know that it's convergent rather than common ancestry because (among lots of reasons, but this is a neat example) it's a different finger. But, they both had fingers to elongate in the first place. So, given the same machinery to evolve and the availability of similar ecological niches (no woodpeckers, lots of bugs) they came up with a smiler solution. We know that brains, and their components are very flexible even in a mature organism. So it makes sense that evolution is wild and creative, repurposing the tool constantly. I mean the diversity in sense perception in different animals seems like evidence of radically evolving brains over relatively short periods of time. Even entirely new senses (eg echolocation) seem to evolve fairly easily and quickly. TLDR: depending on what your precise definition of "brain" is, this seems very likely. Aye-ayes & striped possums both have elongated fingers that evolved separately from regular fingers. The fact the they both evolved from regular fingers is interesting, but neither here nor there for most interesting conclusions. Brains are probably like this, but way more interesting any mysterious. ^I feel like I have to credit Douglas Adams who wrote beautifully about these animals.
- caf 11y ago
  So I was using "brain" in the same sense as the article, as a shorthand for "central nervous system". I think we already knew that once you acquire a CNS, it can evolve rather rapidly to quite complex brains, and that doesn't seem intuitively surprising. It's that first leap to a basic nervous system which seems like the high activation energy barrier, and if it may have happened twice rather than just the once, then I find that interesting.
  - netcan 11y ago
    The 'earliest known example' (520mya) discussed dates to around the cambrian explosion, the geological period where the fossil record is rich with "earliest examples" and type specimens for phylums. Maybe another way to put it is 'The definition of brain used in this article might apply to organs other than the brain in modern species." It's basically a nervous system, centralized or not. Who knows what it did or what it was for. It may have a predecessor outside the animal kingdom. Plants have sensory perception, or some version of it. I'm not disputing the claims in this article or anything else. I'm basically agreeing with you. Whether or not some nervous system, nerve cells or complexes of nerves evolved 520+mya and were 'lost' in some phyla or was evolved through convergent evolution a little later, it's partially a semantic issue: do we call something a brain. Most of what makes a brain a brain probably came later and evolved separately in different phyla. This means radically different ways of doing things. BTW, Richard Dawkins really turned me on to evolutionary biology (a side gig, when he's not arguing with dummies) in some of his books. "Ancestors Tale" is awesome for really getting the "phylogenetics" way of thinking discussed here.
- a_bonobo 11y ago
  Interesting that you chose cephalopods - their eyes work similarly in the "basic layout" to vertebrate eyes but cephalopod eyes have a few key differences, which may again be convergent evolution, since the most recent common ancestor didn't have eyes, only a photosensitive spot (which is still present in jellyfish).
- agumonkey 11y ago
  > Cephalopods are very distantly related to us. Our last common ancestor with cephalopods is also our last common ancestor with slugs and hookworms. Yet many species are obviously highly intelligent. Their intelligence seems to work very differently from vertebrate intelligence. Similarly old low bit-width CPUs are "as" potent as nowadays CPUs according to the work/dataflow they have to handle. Or even OSes, win95 could do a lot that a recent Linux/WM can do at a tiny fraction of the structural cost/complexity. Also text encodings.

spiritplumber 11y ago

For the same reason why, say, version 7 of the WRT-54G router had half the memory that version 2 had. It's expensive (money or calories) and the extra functionality doesn't help in getting more out there (selling or reproduction).

WalterBright 11y ago

Plants have also survived for hundreds of millions of years with no brains.

deleted 11y ago
[deleted]
grondilu 11y ago
Indeed. My memory is failing me but I seem to recall having heard or read someone talking about the brain and stating that its sole purpose is to move the body. Thus, an organism that does not move does not need a brain, and as a proof of this idea he mentioned that some animals, like some medusa, loose their brain once they fix themselves to the floor (turning into polyps in the case of medusa).
- joeyo 11y ago
  Daniel Wolpert has a TED talk where he makes this point [1]. And I think he's basically got it right. Certainly there are organisms that can move without a nervous system (single celled amoebas, venus fly traps, etc) but by and large you need an (electrical) brain if you are going to react to something on a fast timescale. 1. http://www.ted.com/talks/daniel_wolpert_the_real_reason_for_brains http://www.ted.com/talks/daniel_wolpert_the_real_reason_for_...
- smorrow 11y ago
  Well. To move the body to which your genitals are attached.
netcan 11y ago
Do we know that for sure?

holychiz 11y ago

what?! no joke about our bosses? oh right, you're all your own boss here. :)

beaner 11y ago

Another example of where more brains doesn't necessarily mean evolutionary advantage is modern humans. It can be seen all over the world that the less intelligent procreate more. The intro to Idiocracy makes the point well: https://www.youtube.com/watch?v=hL1-340ODCM https://www.youtube.com/watch?v=hL1-340ODCM It's kind of a joke, but also really not. It's frightening.

MichaelGG 11y ago
But that relies on smart people having figured stuff out to the point where it is no longer an advantage. If human intelligence declined to the point where we lost that kind of knowledge, then being smarter could probably become a benefit that's selected for. Rinse, repeat?
- beaner 11y ago
  Yeah, we did have a dark ages that lasted for a thousand years. Nothing says the same thing can't happen again.
givan 11y ago
Why being poor or living outside western culture means less intelligent?
- beaner 11y ago
  First, I never said anything about western culture. (Note that the example is inside America.) Second, the poor generally don't have the same access to good education so in general it is true. Third, I edited my comment because I know they're not equal and it was a mistake.
vog 11y ago
> It's kind of a joke, but also really not. It's frightening. It is a joke. Idiocracy relies on the assumption that the "more intelligent" people are snobs and too busy and too perfectionist with their life to have children, while the "less intelligent" people are mostly having sex and are too lazy to apply contraception properly. Essentially, the first half of the movie is a justification for elitism. I'm less afraid of Idiocracy to become true, but more afraid of politicians acting as if they believed in this movie. The second half of this movie is more interesting, though. It may be interpreted as an analogy of how the most gifted people (in the sense of "intellectual giftedness") may feel living in today's world. (by putting today's "normal" people into a dumb world) But even that is, of course, a funny hyperbole, and nothing to take too seriously.

edem 11y ago

So if someone does not use his brain for long he/she becomes demeted becuse he does not need a brain?

skywhopper 11y ago

Key point: evolution does not necessarily working towards more complexity or a specific endpoint. Rather, the unique selection pressures that exist when organisms attempt to reproduce vary, as do the particular genetic changes that happen due to any number of factors (mutation, viruses, gamma rays, copy errors, bacterial absorption, whatever). Each generation may face similar or different pressures. Certain mutations may be more or less likely. In some cases, the mutations that survive may be pure random chance. In others, only a specific mutation may have saved the organism's particular genes from extinction. The future organisms and genes that emerge from this chaotic process are unpredictable. Sometimes those organisms will lose features, sometimes gain, sometimes have weird changes that don't appear to make sense. All that matters is: do the organisms continue to reproduce successfully generation after generation?