Arthropod head problem | Hacker News Reader

Arthropod head problem

en.wikipedia.org

60 pointsraattgift22 comments

I read about this somewhere recently and now I remember - it was "User: Junnn11" on the front page of HN a few weeks ago for their arthropod illustrations (see https://news.ycombinator.com/item?id=35630423 )

Arthropod Head Problem is a really good name for a band

Worth checking out the talk page. Looks like this whole article is out of date and that much of the problem is resolved.

The article doesn't mention phylogenetic evidence at all. That makes me think that this issue may be completely resolved/rendered irrelevant by more recent phylogenies.

While not exactly related a significant contribution has recently been published- https://pubmed.ncbi.nlm.nih.gov/37094905/ in a journal. Tools like this help tease out what things "really" are, as they give a hypothetical context (as opposed to claiming one-true-truth) to help one think about things. Evolution has repeatedly converged on what people would say are the "same" thing many times, this is well understood. Deeply understanding the vastness of biologically diversity, as others have alluded to in the comments, is still relegated to such a tiny minority of human minds that finding a common language to express the nuances discovered with the rest of humanity remains a challenge.

I don’t see how humanity can go on without a solution to the arthropod head problem. The taxonomy might not be correct!

Considering that we can trace genetic diseases all the way through arthropod models through other model organisms to humans I can't agree more ;).

Wow, my eyes fully glazed over trying to just skim that article. Wikipedia has a rule about not over-using jargon, especially in highly technical articles. It looks like some expert attention is needed there to tone that down and translate all that to common English.

I wanted to redirect you to the Simple English version, but there is only Esperanto...

I mean, there is only so much you can simplify on some topics, and this is a really specific topic. Making every domain-specific term a hyperlink is about as good as you can hope to get sometimes.

This should have some simpler overview though. I actually have some background in morphology of insects and crustaceans, and skimming first screens for a couple of minutes gave me no idea what is it about.

Looks like it's about the evolution of arthropod head from segmented worms, with disagreements on what arthropod parts are homologous (evolutionary correspondent) to which parts of segmented worms. Please correct me if I'm wrong.

I don't actually think it's really a jargon problem per-se in this case. I think there's some minor changes that would help a lot.

For example, the very first sentence: "The (pan)arthropod head problem[4] is a long-standing zoological dispute concerning the segmental composition of the heads of the various arthropod groups, and how they are evolutionarily related to each other". So even if you understand the jargon more or less, the way this is written makes it feel like "there's a lot more essential detail" that's not covered in this sentence. But once you read the background section, and you get to this sentence "The challenge that the arthropod head problem has to address is to what extent the various structures of the arthropod head can be resolved into a set of hypothetical ancestral segments", you realize that actually the initial summary is actually fairly complete, but just strangely uncommital.

Rewriting the first sentence to be more direct might result in: "The arthropod head problem is a zoological dispute over the extent that the various structures of the arthropod head amongst different types of arthropods can be resolved into a set of hypothetical ancestral structures". Or maybe a less aggressive change: "The (pan) arthropod head problem is a zoological dispute over the segments that make up the heads of the various arthropod groups, and how these different segments are evolutionary related to each other".

The background section itself could probably be improved by moving the first sentence deeper into the section, and probably doing a paragraph break right before the "The challenge that the arthropod head problem has to address.." sentence to make it easier for skimmers (or glazed out readers) to pick out a significant segment.

In fact, maybe the problem with the beginning section is that it's focused on the "meta". Every single sentence contains information about the history and development of "the problem", while only one sentence directly talks about "problem", and like two sentences talk about the scope and some of the tools used to address the problem. Perhaps portions of the "Background" section should be raised to the top level, and the history stuff moved to a history (or even the background...) section.

I think it's reasonable for some articles to be pretty jargon dense, but the opening bits should make some accommodations to less specialized audiences.

Bravo.

Most people suck so very much at writing clearly and concisely.

And that usually has little to do with assuming knowledge in the audience; people who have the requisite knowledge are just better able to penetrate the bad writing, but would still be able to digest a better article much more quickly.

SGTM. How about you make some of those changes to the article? Of course you may end up with possessive authors who revert, but the Edit button is there for a reason :-)

As far as I can tell the reason is to give those possessive authors something to do.

Well, from the comments here, it looks like "there's a lot of debate on which parts of various insects' heads evolved from the same ancestral parts" about covers it.

Encyclopedias are not supposed to be technical references. They are for laypeople to get a general understanding of something. Linking to another domain-specific resource won't really help.

I'm not a biologist but it seemed fine to me.

In short, animal bodies can be constructed either as a chain of repeated basic structures called segments or otherwise. We could think for example in an earthworm and a jellyfish.

All segmented animals can be represented as a list of ordered segments. Different lists can have different lengths, but the number of elements inside each type of animal is very stable. We are segmented animals also.

An hypothetical animal with five segments in its body plan, would be represented as:

'(1 2 3 4 5)

Each element in (cdr '(1 2 3 4 5)) has the ability to grow a couple of structures called appendix. The first segment will bear another special type of sensors designed to detect light, the eyes. Animals use chemical gradients to modulate the appendix separately and turn them into everything that will need, in the right place.

The concept of chemical gradients is not difficult to understand. Drop some chemical in the first segment and let it to diffuse towards the end of the chain. The first part will receive much more chemicals than the tail, activating different genes. Our embryo now looks like this:

'(head torax abdomen)

Rinse and repeat for each element, nesting lists. This very smart process is all that we need to make an animal while guaranteeing that our embryo will never develop a couple of ears in the legs [1].

[1](... Unless is an arthropod, because each type of animals have their own ways to solve the problems)

Arthropods are a very species rich and very diverse group of animals, but using this system we can safely classify them into several big categories by the type, class and position of its appendix in the list.

In the real life this translates to:

'( antenna leg leg leg)

This is an hexapod, for example an ant, but:

'( fake-antenna leg leg leg)

This is Myrmarachne a spider mimicking an ant. It moves its first pair of legs to simulate an antenna and trick its preys, but we know that the structure is different. If you are an ant, you would be dead by now.

'( antenna antenna antenna leg leg)

This animal does not exist. Not in this planet. Is an alien.

If we have a partial fossil with one leg and a couple of wings, we can say that this was a modern insect. Wings developed only in the modern insects.

The appendix and its location are so different among the main groups of arthropods and so fixed inside the groups that we can safely say that trilobytes didn't fall in any known category of alive arthropod. Those were not crustaceans and all went extinct.

We also know that spiders are not just crustaceans that lose a couple of legs and a couple of antennas. Its legs are placed in different segments, and the auxiliar structures in its head are totally different.

The whole article reads like it was paraphrased by somebody who doesn't actually know anything about the subject.

weird I put this one last month https://news.ycombinator.com/item?id=35635187

Yeah, sometimes stuff will get reposted like 5 times in a row before anyone notices it.

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