Exception, not the rule, but I did warn it was a relatively good empirical formula, not a law of nature :-)  I am of the mind that categories such as species are mental constructs to turn the phenomenal world into an approximate model-space so that understanding and action planning can be improved.<p>So for me rather than concepts like &quot;species&quot; being meaningless, they can have meaning (or at least value), but best not to think of them as iron laws.  Mostly the point I was hoping to get to in my root response before I diverted myself reading my own text while typing it.<p>It&#x27;s easier to create iron laws for categorical manipulation than it is to place observations into categories to begin with.