
What the Ctenophore says about the evolution of intelligence - Symmetry
https://aeon.co/essays/what-the-ctenophore-says-about-the-evolution-of-intelligence
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finnh
One of the ways that science has demonstrated the ancient roots of serotonin
is by giving octopuses MDMA[0], resulting in the normally wary creatures
getting all cuddly.

[0]
[https://www.nature.com/articles/d41586-018-06746-x](https://www.nature.com/articles/d41586-018-06746-x)

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HNLurker2
Wow that sounds ridiculous but true

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tempguy9999
I can't make sense of this:

"Moroz reached this conclusion by testing the nerve cells of ctenophores for
the neurotransmitters serotonin, dopamine and nitric oxide, chemical
messengers considered the universal neural language of all animals. But try as
he might, he could not find these molecules. The implications were profound."

But plants make and use serotonin and dopamine

Phytoserotonin also plays a role in the following aspects of plant function:
Growth regulation Xylem sap exudation Flowering Ion permeability Plant
morphogenesis Regulation of ripening

from [https://www.news-medical.net/health/Serotonin-in-
Plants.aspx](https://www.news-medical.net/health/Serotonin-in-Plants.aspx)

and

The functions of plant catecholamines [seems to be a ref to dopamine] have not
been clearly established, but there is evidence that they play a role in the
response to stressors such as bacterial infection, act as growth-promoting
factors in some situations, and modify the way that sugars are metabolized.
The receptors that mediate these actions have not yet been identified, nor
have the intracellular mechanisms that they activate

from
[https://en.wikipedia.org/wiki/Prolactostatin#Plants](https://en.wikipedia.org/wiki/Prolactostatin#Plants)
and

Plants and animals diverged ~1.7 billion years ago, which is plausibly why
they share these neurotransmitters, yet the article seems to say we diverged
from ctenophores ~ 0.5 billion years ago "If Moroz is right, then the
ctenophore represents an evolutionary experiment of stunning proportions, one
that has been running for more than half a billion years"

So unless serotonon and dopamine evolved in plants and animals after the split
between plants and animals, (or somehow ctenophores lost these after they
split from us) how is this possible?

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ncmncm
Evidently ctenophores don't use serotonin anymore, and have found some other
molecule they like better for what they are doing. There is nothing special
about the molecules we use, they just happen to fit the receptors we use, so
switching would require changing both, which is too hard to bother with.

If you haven't watched youtube videos of ctenophores eating one another yet,
you are in for a treat.

~~~
acqq
Thanks!

> youtube videos of ctenophores eating one another yet, you are in for a treat

[https://www.youtube.com/watch?v=MmoChWQ6xCk](https://www.youtube.com/watch?v=MmoChWQ6xCk)

~~~
ncmncm
[https://www.youtube.com/watch?v=1xkNPp6mzzI](https://www.youtube.com/watch?v=1xkNPp6mzzI)

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modwest
This article is deeply unsatisfying. Too much fluff for a very basic point:
ctenophores are different kinds of organisms than we’ve come to expect. That’s
it. “Different” appears 24 times in the article, almost every single instance
of which is just, “ctenophores are different.”

There’s not much more information in this article than that. I was hoping for
some compelling science writing. But this feels like a tiny story (for now)
stretched way too far. In a year or five when there are some interesting
hypotheses about WHY they’re different, then we’ll see.

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SamBam
I think you're missing the key point (and perhaps the article doesn't explain
it clearly): if the nervous system is completely different from other animals,
then that implies (maybe) that the nervous system did not just evolve once,
and then branch from there, but evolved multiple times, each time slightly
differently but with similar results.

This is called "convergent evolution," and is fairly common (though not
necessarily common for big systems like the nervous system), but what it
implies is that there is something fundamental about the structure of the
nervous system that leads it to being evolved again and again, even if in
slightly different versions.

Contrast that to other things that are evolved, let's say endoskeletons
(bones). These seem fundamental to us, but (as far as I know) they only
evolved once, and it would be perfectly reasonable to imagine a world where
they never evolved, and all the animals had exoskeletons.

Indeed, if endoskeletons really only evolved once, then we might really have
no reason to expect them in any alien species. But if something like the
nervous system evolved multiple times, then we expect that to be a solution
that evolution finds again and again.

~~~
modwest
Yeah, I understand all that going in to the article. I have, let's call it, an
advanced beginner's understanding of neuroscience & evolutionary biology.

It was just an extremely long article, in my personal opinion, for "this is
different."

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radford-neal
Ciliates, such as paramecium, are another interesting group with a completely
different approach to life. They are usually described as "single celled", and
by implication simple, but the cell in this case is much more complex than one
of ours.

Animals (and for that matter, plants) develop from a single-celled zygote,
into a multicellular organism, which eventually dies, after producing gametes
to merge into zygotes to continue the cycle.

Ciliates have an analogous, but totally different, approach. A newly "born"
ciliate has a "micronucleus", similar to one of ours, from which it makes
multiple copies of its DNA to form a "macronucleus", which does all the work.
Perhaps gene expression in the macronucleus even changes in a way that learns
about its environment. But eventually, the ciliate mates, or goes through a
sort of self-conjugation event, dividing into more than one cell, each of
which gets a new micronucleus formed by recombination. These cells discard the
macronucleus, forming a new one from the new micronucleus.

It's sort of like a multicellular organism dying, since whatever the old
macronucleus learned will be forgotten. (Perhaps that's the point, if the
environment has changed, requiring a new approach.)

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keithnoizu
I think a possible caveat is the Ctenophore had to continue to reproduce in an
environment where other organisms possessed a central nervous system and
intelligence. Although I don't think it is likely, it could be the case that
evolving to that level of complexity is unlikely but once one successful
organism in the ecosystem possesses it, it exerts evolutionary pressure on
other organisms to move towards the greater complexity as well.

