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Comment by throwaway2048 | Hacker News Reader

throwaway2048·

>"birds" are essentially defined as the set of theropod species that survived the K-T extinction.

This is not a definition of birds that is scientific or even colloquial. Nobody defines birds this way.

Also, we only consider the extinction to be "over" (the point at which we can declare who is and is not a survivor) when the only theropods left were birds, so this definition is circular. This is the problem with trying to derive necessary and sufficient conditions for things like "birdness", the concept was constructed by pattern matching, not analytically, so rarely will an analytic definition capture everything that the common sense understanding encompasses.

All of taxonomy is pattern matching unless you have something like kennel clubs or Mormons tracking individual genealogy

We're not talking about the same "pattern matching" because even those examples are pattern matching. You have breeds of dogs and a dog is either one breed or another or it's a hybrid/mutt. But at what point in the process of creating a new breed do you switch from handling hybrids of existing breeds to handling purebreds of your new breed? No single generation seems like it could be enough to make the difference, since the puppy is just as similar to its parents as the puppies of any other generation, but on the scale of many generations, a new breed clearly emerges. It's analogous to the paradox of the heap [1].

Derek Parfit's Reasons and Persons engages with this problem as it applies to personal identity with his "spectrum cases".

[1] https://en.m.wikipedia.org/wiki/Sorites_paradox

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