I have read that it can be proven experimentally and it occurs to all fermions.

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    $\begingroup$ One does not simply "mark" an electron. I assume you're talking about $SU(2)$ being the double cover of $SO(3)$. $\endgroup$ – Danu Sep 6 '15 at 8:02
  • $\begingroup$ This is easily answered by a search of this site, though to be fair you need to know the electron is a spinor to know what to search for. $\endgroup$ – John Rennie Sep 6 '15 at 9:49