A tiny sea creature is the earliest known step in humans’ evolutionary history | Hacker News Reader

A tiny sea creature is the earliest known step in humans’ evolutionary history

researchgate.net

45 pointsdiodorus19 comments

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

[2]: The clever observer will note that this means that technically, very early on, each of us is little more than an arsehole ;)

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. :)

So what you are saying is that nature ALSO shuns multiple inheritance? :)

Yes, but have you tried reading the codebase?

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 ). Vast majority of animals fall into one of these two groups, though not all, for example https://en.wikipedia.org/wiki/Cnidaria .

Anyway, quite agree this is a fascinating discovery!

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.

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...

> 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.

So this this headline wrong?

https://www.theguardian.com/science/2017/jan/30/huge-mouth-a...

Is it actually a huge anus with no mouth?

A heard about this, it has a large mouth that it excretes though. I know a lot of humans that still do that

The cynic in me has doubts whenever Chinese scientists claim China is home to the missing link.

I imagine if this was discovered in, say, Argentina, then there'd be a good chance of some Argentinian scientist participating in the discovery.

Call it the anthropic principle of archeology :)

I can't speak for the GP, but one might make a reasonable distinction between the reliability of findings that come out of Argentina as they compare to those from China.

Edit: Someone doesn't appreciate this comment. Astute professional analysts the world over know that official figures that come out of China are among the least reliable on the planet.

And while scientific misconduct is not unheard of anywhere, China's hardly a shining example in that regard.

Lastly, good Chinese research agencies themselves are having a difficult time keeping up with numerous bad actors who are doing their best to fraudulently publish papers.

This isn't xenophobia, it's a fair appraisal of the sometimes inconsistent qualities of the world's societies.

What kind of misconduct? There is a big difference, for example, between plagiarism and fabricating results.

And which percentage of the researchers are involved in this? 1%? 0.1%? 0.01%? Do you have any studies you could link to that in any way quantify this?

China's research spending and number of research articles produced today is second only to the U.S. There are always going to be some bad apples among that many researchers. That should in no way discredit the rest of the profession.

Last year, 80% of the applications for new pharmaceuticals in China were found to contain fabricated, flawed, or inadequate clinical trial data: http://www.sciencealert.com/80-of-the-data-in-chinese-clinic...

Well put.

I don't see them claiming to have found the missing link. In any regard, biologists are unlikely to use the term 'missing link' since it implies evolution is discontinuous, which is a common mistake the layman makes.

Yay, 'Murica!

It looks like chest breaker from alien

Reply on news.ycombinator.com