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Wow. I would have bet on the sponge-sister scenario all night long. Sponges have no neurons. This finding implies that either neurons were “lost” on the sponge lineage, or neurons evolved convergently in comb jellies and us (parahoxozoa). Both possibilities seem pretty interesting.
It is highly likely that the common ancestor of the sponges and of the other animals except comb jellies did not look at all like a sponge, but it was a mobile ciliated animal, which was much more similar to a sponge larva (which is mobile) than to an adult sponge.
The sponges have developed their own way of life, where the adults are immobile and fixed and they feed by filtering the water, like many other groups of animals, for instance clams or sea squirts.
All such groups of sessile filtering animals have greatly simplified bodies and very reduced nervous systems.
Because the ancestor of the sponges was already much simpler than the ancestor of clams or of sea squirts, they are the simplest of all.
While sponges do not have neurons, they have most of the genes required by neurons and there are good chances that the ancestor of the sponges had neurons.
The fact that sponges are more closely related to humans than comb jellies is exactly analogous to the fact that the sea squirts are more closely related to humans than the lancelets.
While both comb jellies and lancelets appear more similar to humans than, respectively, sponges and sea squirts, that is only because both sponges and sea squirts are simplified due to their sessile water-filtering way of life.
> All such groups of sessile filtering animals have greatly simplified bodies and very reduced nervous systems.
Yes, as the joke goes, as the larva of an anemone settles into its permanent feeding spot it will consume its own brain, much like the professor that has finally achieved tenure.
I thought it was tunicates (sea squirts) because they are closely related to vertebrates and start off free swimming with a notochord. (I also heard the joke as being about Americans- they are curious and thoughtful while young, but then settle down, become couch potatoes in front of the tv and digest their own brains). Either way, it is a cute joke and interesting marine biology.
> tunicates (sea squirts)
Could actually be.., perhaps I am miss-remembering :)
Tunicate is more likely. the Anemone larva result tiny medusa and both larva and adults have nerve networks.
Tunicates and Echinoderms seem to have evolved from bilateral ancestors like the ancestors of chordates.
There is also the question of where to put Placozoa, they still might be the true sister group to all others. But these are so simple and little known that there might just not be enough data to know for sure. If we disregard Placozoa, I would also have bet on the sponge-sister scenario.
You are the latest in an unbroken line of reproduction all the way back to the first complex life 600 million years ago.
Great, and here I am not having kids
Ah, but eusociality means that the genes you have are in kin that inherit the world you leave them. So, by all means, leave them a better world!
That’s literally cuckoldry
There have been billions of organisms that have not reproduced during their life. Almost all of them didn't choose that path. Evolution cares about the survival of the species, not the individual. You can contribute to that without having your own kids.
Yet the society you contribute to works to ensure your species perpetuates itself (and >99% of your DNA) into the future.
Well, even beyond that, to ~3.5B years ago.
Well, one of the latest.
I'm not involved in biology as a field in any way but I found the open-access article Cavalier-Smith, 2017, The Origins of Animal Multicellularity to be an excellent article for interested laymen like me back when this was just a hypothesis.
If anybody wants to go looking: https://royalsocietypublishing.org/doi/10.1098/rstb.2015.047...
It seems like a bit of a free-for-all at the moment with genetics - commoditised whole genome sequencing has burst open the field for making discoveries. Very exciting.
A bit like a few years ago any teenager who knew a bit of deep learning could improve on state of the art in almost any domain [0] that hadn't used deep learning yet.
Compare also https://slatestarcodex.com/2016/11/17/the-alzheimer-photo/
[0] Any domain where deep learning is applicable.
Unless they find another one, closer to that original trunk in the tree of animal life.
They studied exactly two sponges and two comb jellies.
Perhaps there's a microscopic organism, or a sea squirt or something as yet unclassified in the ocean.
But for now, cousin Comb Jelly takes the crown!
I knew these two slimy colleagues of mine had something in common ........
That’s your great, great great, great etc grandpa right there.
No, that's exactly what it is not. 'Sibling group' implies that there is no direct line of descent, but that at some point the tree of life forked, that Comb Jellies are in the one fork and that all the rest of the animals (including us) are in the other.
Does it mean that every form of life on Earth (right now) evolved from the "Parent" of the Comb Jelly ?
No, just animals. Not prokaryotes, archaea, amoebozoa, etc.
Not the parent, but some great-grandparent, yes.
See https://en.wikipedia.org/wiki/Last_universal_common_ancestor for more info:
> The LUCA is not the first life on Earth; it may have lived among a diversity of other organisms whose descendants all died out. Rather LUCA is the most recent form from which all surviving life on Earth is descended.
No, there are many forks before that one.
If this stuff interests you I would like to recommend Dawkins' 'The Ancestor's Tale', it is pretty accessible and walks you back through time step-by-step.
So it's my ultra-uncle
You may be taking this more seriously than my comment warrants.
More like your 30+ millionth cousin.
That's great.
This thing has the coolest warp bubble I've seen.
Wish I knew more about biology. I tried a couple of introductory molecular biology lectures and while I found them very interesting, both times I started feeling quite lost by the 3rd hour. So much chemistry and physics to learn. I wish I was smarter and better educated