Science: seeking examples of distinctions that are useful but spurious

There’s no easy way to define a continent (other than “Europe, Asia, Africa, North America, South America, Australia, and Antarctica”), but it’s still a useful concept to have.

Right. Sure, from a skeleton a expert can often determine most likely "race’- but not by any means always.

It’s a poor and simplistic system, that is still useful at times, no doubt. For example, for a short description of a wanted person where there is no photo available. Even there, it could be misleading and worse than useless.

Well, either free will exists, so it’s okay to punish people for their actions, or free will doesn’t exist in which case we have no choice but to punish people for their actions since we can’t choose not to do so.

To some degree the branches of science are spurious. When you boil it down, it is all physics. Distinguishing biology from chemistry is useful though, but the existence of biochemistry shows that there is not a solid line between them.

Thank you all for disabusing me of my naive categorical view of the world. In all seriousness though of course I understand that things are fuzzy in the real world; I should have clarified that my interest is more in theory-internal distinctions. You’ve all provided me with some good examples but I think my favorite is robby’s on electromagnetic radiation, where the money line on Wikipedia is (bolding mine):

[del]The planet[/del] Pluto understands and agrees.

There is no scientific evidence that Homo sapiens is different from other mammals or primates in any qualitative biological way, but it seems very useful to regard humans as being somehow distinct from species deemed “lower”.

Umm, no, Homo Sapiens is pretty obviously a species distinct from any other living species.

Bode’s Law, which seemed like it was just playing with numbers until planets were discovered where it predicted them. It’s still useful as a mnemonic for the distances from the sun to the planets.