What the Ctenophore says about the evolution of intelligence
aeon.co
aeon.co
"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
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 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?
So it would seem as if the ctenophores lost the ability to produce these chemicals, and went on to develop a nervous system that didn't require them.
But the article is really about the evolution of the nervous system, and so the pertinent question is whether (a) the evolution of the nervous system was more recent than 0.5B years ago, in which case the two nervous systems evolved independently, or whether (b) the nervous system evolved earlier than that, and then the evolution of the ctenophores adapted its nervous system to not require serotonin and dopamine.
I think the article is suggesting (a).
1. https://www.sciencedirect.com/science/article/pii/S156973391... 2. https://en.wikipedia.org/wiki/Serotonin#Comparative_biology_...
I wonder if Moroz is harming his case by stretching it too thinly -- small differences do not necessarily require independent origins -- but I am not a biologist.
If you haven't watched youtube videos of ctenophores eating one another yet, you are in for a treat.
> youtube videos of ctenophores eating one another yet, you are in for a treat
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.
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.
It was just an extremely long article, in my personal opinion, for "this is different."
If life came to earth on meteors, there might be life from different corners of the universe on earth.
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.)