Why is the sound of fingernails on a chalkboard so intolerable? I am curious as to what current research shows regarding why scraping noises such as fingernails on a chalkboard, a knife/fork scraping against a plate, metal grinding against metal or stone etc are so intolerable to humans. In doing some initial research for this I read the wikipedia article on Sound of fingernails scraping chalkboard (there's a wikipedia article on everything!) but I am looking for more references or updated research.

From the reading I have done, there seems to be two competing theories:


The sound is reminiscent of the warning calls of primates and triggers an evolutionary response left over from an earlier age designed to protect us from predators
The sound hits a resonante frequency of the inner ear which causes it to be particularly intolerable


To me personally the first theory makes very little sense. Hearing the warning calls of primates does not personally trigger anywhere near the same feelings of extreme frustration and irritability that I feel when I accidentally scrape my knife on my plate. Furthermore the feelings caused by the "nails on a chalkboard" sound do not at all trigger a fight-or-flight response or put me on edge as a loud noise or something that startles me does. If anything it is almost paralyzing, which seems counter to the evolutionary theory.

How accurate is the wikipedia article? Is there any newer / more widely accepted research available on what causes the sound of "fingernails on a chalkboard" to be so intensely awful to human beings?
My initial thoughts are that the sound produced a dissonant sound, that is (from the link):


  "An unstable tone combination is a dissonance; its tension demands an onward motion to a stable chord. Thus dissonant chords are 'active'; traditionally they have been considered harsh and have expressed pain, grief, and conflict."


—Roger Kamien (2008)

According to the article "Psychacoustics of a chilling sound", (Halpern et al. 1986), it is the low frequency components of the sound that cause the most discomfort. In their tests, removing the low frequency part in a digital simulation, made the sound a bit more bearable.

In the conclusion of the article, there is some support for the Wikipedia article that Josh Gitlin linked to in his question:


  the complex acoustic stimulus pictured in Figure I
  very closely resembles some of the spectrograms of warning
  cries emitted by macaque monkeys (Green, 1975). As
  another possibility, the signal may be similar to the vocalizations
  of some predator.