TDLR: Biology has no consistently applied definition of "species." The field operates on vibes, reverse-engineered justifications, and conservation politics. I propose a litmus test: any species definition that, if applied consistently, would split Homo sapiens into multiple species is wrong. This kills the Biological Species Concept, the phylogenetic species concept, and most morphological/ecological criteria. What survives is something close to "gene flow between them is biologically impossible," which lumps a lot of species currently recognized by the IUCN back together.

Part I: Definitions

Definitions need to carve reality along its joints

For those with a passing familiarity with semantics, it's popular to say that you can define a word however you want, that reality is a continuum and all lines subdividing it are arbitrary. One culture's sea-blue is another culture's wine-dark.

This has the virtue of being true, in a strictly philosophical sense. In all other ways, however, it's false. It's true that you can create a word that means whatever you want. You can make a new noun called a “mumpston” and define it as “all radially symmetrical red things manufactured in Laos, and also frogs.” There's no law of linguistics stopping you. You have looked at reality [...]

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Outline:

(00:51) Part I: Definitions

(06:16) PART II: Splitters and Lumpers

(14:29) PART III: A Definition of Species

(43:28) PART IV: Implications, or the Lumpers were right!

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First published:
February 24th, 2026

Source:
https://www.lesswrong.com/posts/oMWXqoCCXYxbGtcWW/wildlife-biology-forgot-how-definitions-work

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Narrated by TYPE III AUDIO.

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“Wildlife Biology forgot how definitions work” by David Goodman

LessWrong (30+ Karma)