What is a human? A miserable little pile of clades

http://approximateknowledge.net/misc/2026/06/13/clades.html

by evakhoury • 1 month ago

17 3 1 month ago

approximateknowledge.net

mdlxxv• 1 month ago

But enough talk... Have at you!

TheWrongGuy• 1 month ago

Every jumbled pile of person has a thinking part that wonders what the part that isn't thinking isn't thinking of

adrian_b• 1 month ago

It should be noted that the list of clades enumerated in TFA is just a summary.

In zoology, there are many other named clades intermediate between those listed in TFA.

Also, in recent years it has become very doubtful that one of the clades listed in TFA, "Deuterostomia", is really a clade.

The deuterostomes are supposed to be the union between chordates (which include humans) and echinoderms with their relatives (a clade named Coelomopora or, less appropriately, Ambulacraria).

There exists only one shared character that seems to indicate that the deuterostomes form a clade: their common ancestor had some slits that connect the pharynx to the exterior, allowing the ingested water to be expelled, for the purposes of filter feeding and respiration. Those slits correspond to the gills of fish and to the ears of humans (the ears are connected to the pharynx, i.e. to the throat, through the Eustachian tubes, which you use to equalize the air pressure on your eardrum).

However, it is possible that the deuterostomes are not a clade, because those pharyngeal slits could have existed in the common ancestor of many more groups of animals, like Spiralia (which include mollusks and segmented worms) or Ecdysozoa (which include arthropods and roundworms).

If that were true, the ancestors of all those groups of animals must have lost their pharyngeal slits when they changed their manner of feeding from filter feeding to predation or deposit feeding.

For now, it is not known with any certainty whether the chordates (including humans), belong in a clade together with the echinoderms or in a clade together with the mollusks and arthropods.

If eventually it will be discovered that "Deuterostomia" is really a clade, that would imply that the ancestor of echinoderms was significantly more complex than its descendants (e.g. by having a central nervous system) and that the echinoderms and their relatives have been greatly simplified due to a sedentary way of life and to the use of passive defense means (i.e. having a hard exoskeleton or living in a protective tube or living buried in the sand).

While there are many other characters that are shared by chordates and echinoderms, there is no doubt that all of those are primitive characters, which do not prove any shared evolution and which were lost in the ancestors of spiralians and ecdysozoans, which have diverged from their ancestors much more than the chordates and the echinoderms.

What is a human? A miserable little pile of clades

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