The Scratching Fingernails on the Blackboard

The sound of fingernails on a blackboard is similar to the alarm signal of our close relatives, the chimpanzees and the bonobos. We split off about 7 million years ago from a line that led to the chimpanzee-bonobo lineage. And so that signal of, I'm making this noise, really bad things are about to happen, just get ready and drop everything you're doing. So that's the evolutionary biology explanation which may or may not be correct of why we find that sound so distressing.