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What I find fascinating about this is that humans and many other branches of the tree are Deuterostomes[1], which means that when the cells first divide the fir

by NamTaf 10y ago

What I find fascinating about this is that humans and many other branches of the tree are Deuterostomes[1], which means that when the cells first divide the first 'hole' goes on to form the anus [2], rather than the mouth. This is in contrast to the Protostomes where the first hole forms the mouth. I mean obviously it makes sense that a single-holed animal used it as a mouth - the anus has no use without the mouth - but (in my naive understanding) it means that somewhere beyond this ancestor, certain groups of vertibrates split and went in opposite directions despite both being (presumably) decended from this thing. It fascinates me that there was some mechanism to cause this, rather than all animals forming in the same order, if we did indeed share a common ancestor that only had one entry/exit hole. [1]: https://en.wikipedia.org/wiki/Deuterostome https://en.wikipedia.org/wiki/Deuterostome [2]: The clever observer will note that this means that technically, very early on, each of us is little more than an arsehole ;)

kkylin 10y ago
I presume that by "vertebraes" you mean "vertebrates"? All vertebrates are actually deuterostomes (see the Wikipedia page [1]), as are echinoderms (sea urchins, sea stars, etc). Insects, etc., are protostomes, meaning "mouth first" (though apparently there is some debate about that, see references at https://en.wikipedia.org/wiki/Protostome https://en.wikipedia.org/wiki/Protostome ). Vast majority of animals fall into one of these two groups, though not all, for example https://en.wikipedia.org/wiki/Cnidaria https://en.wikipedia.org/wiki/Cnidaria . Anyway, quite agree this is a fascinating discovery!
- NamTaf 10y ago
  Yes I did, sorry. Thanks! Edited to fix that. I was of the understanding that some vertibrates were protostomes, but it appears I'm mistaken! Maybe this wasn't a common ancestor then, though it still begs the question how it went from one hole being a mouth/anus combo to a deuterostome.
  - kkylin 10y ago
    Probably no way to know if this critter is an ancestor of ours. Though I'm not a biologist, as far as I know the question you pose remains a mystery...
derefr 10y ago
Personally, I think it's easier to understand the deuterostomes: the "mouth" will benefit from being controlled by input from sensory organs, and those need to be on the outside of the body. Thus, a natural bending of a flattish body-shape into a horseshoe, with the mouth on the outside of the "bend." Also, a fun fact to go with yours: vertebrates are triploblasts. That means, when we first fold over (gastrulize), our cells differentiate into three types--one on the "inner wall" of the fold, one on the inside of the body, and one on the exposed "outer wall" of the fold. In other words: we're all tacos! Another, perhaps more-weird-than-fun fact: our DNA is basically three separate "code bases", one for each layer. It is much easier for a given feature to evolve by differentiating from similar tissue proteins in its own layer, than in another layer. (In fact, to do otherwise, the resulting proteins still have to "start off" in their ancestral layer, before "migrating" during development.) Anyway: our brains--which you'd think of as an "internal" organ--are actually part of the ectoderm, and in lower organisms, the first thing that the ectoderm is, is skin. So, your brain (and your nerves, your spine, and most of your sensory organs) are all effectively "kinds of" skin tissue. Your nerves? Skin with capacitance. Your spine and teeth? Calcified nerves. The reward centre of your brain? Modified skin pigmentation cells. Your retina: also skin pigmentation cells. Your iris: modified retinal cells. Basically, evolution always starts its feature branches with a bit of copy-and-paste programming. :)
- jacobush 10y ago
  So what you are saying is that nature ALSO shuns multiple inheritance? :)
  - zbyte64 10y ago
    Yes, but have you tried reading the codebase?
acqq 10y ago
> the anus has no use without the mouth - but (in my naive understanding) it means that somewhere beyond this ancestor, certain groups of vertibrates split and went in opposite directions despite both being (presumably) decended from this thing. I understand the story differently: there were animals with a single opening. Then the animals with two openings evolved, but more than once, based on the animals we have today, there are at least two different evolution internal mechanisms to more than one opening: it's just how the cellular mechanisms work during the cell division (meaning the "programs" driving them are different). We can't say there were ever "anus-only" animals just as we can't say there were "mouth-only" animals. There were single-opening animals and then there were two internal mechanisms leading to the two-opening animals.
wubbfindel 10y ago
So this this headline wrong? https://www.theguardian.com/science/2017/jan/30/huge-mouth-and-no-anus-earliest-known-ancestor-saccorhytus-coronarious-evolution https://www.theguardian.com/science/2017/jan/30/huge-mouth-a... Is it actually a huge anus with no mouth?

by NamTaf 10y ago

kkylin 10y ago

I presume that by "vertebraes" you mean "vertebrates"? All vertebrates are actually deuterostomes (see the Wikipedia page [1]), as are echinoderms (sea urchins, sea stars, etc). Insects, etc., are protostomes, meaning "mouth first" (though apparently there is some debate about that, see references at https://en.wikipedia.org/wiki/Protostome https://en.wikipedia.org/wiki/Protostome ). Vast majority of animals fall into one of these two groups, though not all, for example https://en.wikipedia.org/wiki/Cnidaria https://en.wikipedia.org/wiki/Cnidaria . Anyway, quite agree this is a fascinating discovery!

NamTaf 10y ago
Yes I did, sorry. Thanks! Edited to fix that. I was of the understanding that some vertibrates were protostomes, but it appears I'm mistaken! Maybe this wasn't a common ancestor then, though it still begs the question how it went from one hole being a mouth/anus combo to a deuterostome.
- kkylin 10y ago
  Probably no way to know if this critter is an ancestor of ours. Though I'm not a biologist, as far as I know the question you pose remains a mystery...

derefr 10y ago

Personally, I think it's easier to understand the deuterostomes: the "mouth" will benefit from being controlled by input from sensory organs, and those need to be on the outside of the body. Thus, a natural bending of a flattish body-shape into a horseshoe, with the mouth on the outside of the "bend." Also, a fun fact to go with yours: vertebrates are triploblasts. That means, when we first fold over (gastrulize), our cells differentiate into three types--one on the "inner wall" of the fold, one on the inside of the body, and one on the exposed "outer wall" of the fold. In other words: we're all tacos! Another, perhaps more-weird-than-fun fact: our DNA is basically three separate "code bases", one for each layer. It is much easier for a given feature to evolve by differentiating from similar tissue proteins in its own layer, than in another layer. (In fact, to do otherwise, the resulting proteins still have to "start off" in their ancestral layer, before "migrating" during development.) Anyway: our brains--which you'd think of as an "internal" organ--are actually part of the ectoderm, and in lower organisms, the first thing that the ectoderm is, is skin. So, your brain (and your nerves, your spine, and most of your sensory organs) are all effectively "kinds of" skin tissue. Your nerves? Skin with capacitance. Your spine and teeth? Calcified nerves. The reward centre of your brain? Modified skin pigmentation cells. Your retina: also skin pigmentation cells. Your iris: modified retinal cells. Basically, evolution always starts its feature branches with a bit of copy-and-paste programming. :)

jacobush 10y ago
So what you are saying is that nature ALSO shuns multiple inheritance? :)
- zbyte64 10y ago
  Yes, but have you tried reading the codebase?

acqq 10y ago

> the anus has no use without the mouth - but (in my naive understanding) it means that somewhere beyond this ancestor, certain groups of vertibrates split and went in opposite directions despite both being (presumably) decended from this thing. I understand the story differently: there were animals with a single opening. Then the animals with two openings evolved, but more than once, based on the animals we have today, there are at least two different evolution internal mechanisms to more than one opening: it's just how the cellular mechanisms work during the cell division (meaning the "programs" driving them are different). We can't say there were ever "anus-only" animals just as we can't say there were "mouth-only" animals. There were single-opening animals and then there were two internal mechanisms leading to the two-opening animals.

wubbfindel 10y ago

So this this headline wrong? https://www.theguardian.com/science/2017/jan/30/huge-mouth-and-no-anus-earliest-known-ancestor-saccorhytus-coronarious-evolution https://www.theguardian.com/science/2017/jan/30/huge-mouth-a... Is it actually a huge anus with no mouth?