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Comment by radarsat1 | Hacker News Reader

I agreed with you until I read the article. It actually makes some really interesting observations about the comparison it's making regarding the typical definition of "head" and how body parts in general relate to gene expression patterns. The images in the article are really cool.

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The article convinced me that starfish bodies developed from heads, just as I'm convinced that primate arms developed from legs, but it didn't convince me that it's appropriate to call the modern forms of these things heads or legs.

If your education includes substantial aspects of evolutionary developmental biology and genetics, then you have important mental models with which you can work with an organism. If you discover that the whole organism is effectively developmentally a head, then it is extremely appropriate to refer to it essentially as a head.

If you instead relate to the organism in its present form in some more mundane ways then it might not seem that way.

Analogies are failing me, but perhaps it would be like realizing an entire government basically spawned out of the centering concept of religious freedom. The structure of it then makes a lot more sense.

I'd say that whale flippers are homologous to legs/feet, but aren't legs/feet. This article says that starfish are homologous to heads, but I'm not sure whether I'd consider their bodies to be heads or not.

This discovery is to our understanding of starfish what Georges Cuvier’s discoveries of vertebrate morphology were to your present understanding of whales.

Words only have meanings in context. It might now be that in the context of developmental biology, starfish have heads. It is surely the case that in the context of millinery, they do not. But no particular context is canonical, and so you cannot say that in an absolute, context-independent sense starfish do or do not have heads.

For legs and their homologues we have the word "limb" (or should I say fins and their homologues? After all, cladistically we're all fish!) but there hasn't been a need for a term for "head and its homologues". At least not until now, I guess.

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