Is scratching (aka the scratching reflex) thought to be inherited from a single vertebrate ancestor or is it something that evolved several times e.g. in birds, mammals etc., i.e. is it a case of convergent evolution?
I suppose this question may be somewhat subjective (what level of scratching is homologous) but since more recently the neurochemical basis for it has become more clear namely that
a molecule known as neuropeptide natriuretic polypeptide b (Nppb) that is released by nerve cells far from the actual itch site triggers an electrochemical cascade that ultimately tells the brain it’s time to get scratching.
perhaps one can ask (the same evolution question) about the signaling cascade for itch-scratch.