Essentialism and such (was a bunch of previous subject lines)

[Carl <Carl@dondwiggins.com>]

>> Triangles can take on an infinite number of variations in dimension 
>> and proportion, for example, and still remain perfect triangles.

>But they can't gain or lose a corner.

>Not so with organisms. Tetrapods can lose all four limbs and stay
tetrapods.

>Why? Because there are descended from tetrapods. There is an essence, 
>but it is descent, not any merely three->dimensional quality. There is 
>no way to ignore time in this question. Tree-thinking. 
>Four-dimensional. :-)

***

Hmm... I smell circularity (or is it a circle?) here...

:-)