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danlowlite comments on Where to Draw the Boundary? - Less Wrong

36 Post author: Eliezer_Yudkowsky 21 February 2008 07:14PM

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Comment author: danlowlite 03 September 2010 03:25:18PM *  0 points [-]

Sharks are considered fish of a certain type, in that they have a "full cartilaginous skeleton," at least per Wikipedia. Contrast with bony fish (e.g., tuna, catfish). Also considered fish are stingrays and such.

This is more of a tangent than a response:

I would suppose that because we are more specific about the shark subset, we can safely make more assumptions on it. I've been told always that sharks were cold-blooded. According to that Wikipedia article, that is a false belief; most sharks are but some are not.

I would agree that it is a translation issue, because that's what language lets people do when they talk/write/etc. But what about internally? What does it say now that I know some sharks (and therefore fish) are warm-blooded? I mean, besides getting pedantic and correct my daughter's teacher when that comes up.

I would appear my previous definition of fish is wrong.

Edit: Removed so many supposes.

Comment author: po8crg 24 March 2012 06:37:30PM 2 points [-]

Fish, like reptiles are paraphyletic. The cladistic revolutionaries want to abolish the category altogether, or reduce it to just the ray-finned fishes - excluding coelacanths, lungfish, the cartilaginous fish (sharks, rays, skates and chimaeras), and the cyclostomes (hagfish and lampreys).

The result is that some sources will use fish as equivalent to the monophyletic group actinopterygii and others use the traditional polyphyletic pisces. Anytime you see a generalisation about fish that isn't true of sharks, there's a good chance that the original source was using fish to mean actinopterygii.

In many ways, it's a more useful classification - 96% of fish species are in actinopterygii, and there is an awful lot of anatomy that is shared by the actinopterygii but not by the rest of the fish. If you're going to exclude cetaceans because they have more in common with land animals than with actinopterygii then why not exclude lungfish and coelacanths for the same reason?