Hearing Pitch: Nature or Nurture

Can you hear the difference between a low note and a high note?

I'm not asking that you be able to discern between an Ab and a G just by listening. I mean, if I hummed at my normal speaking pitch (around middle C), then at my preferred singing pitch (C below middle C), could you tell that the first was higher?

When substituting middle school music for the millenia (9 weeks) I did, I engaged the students in a pre-recorded exercise where all they had to do is listen to a CD playing a series of two tones and circle "Higher" or "Lower" on their papers to indicate whether the second note was higher or lower than the first. Not a hard task, I thought. In fact, most of the examples played the difference between the high end of the piano and the low end of the piano; the exceptions stayed within five steps of each other in pitch.

The test results? Not so good. Could it have been disengagement in the activity? Yes: they were middle-schoolers. But, for an easy grade and an easy activity, most of the students will let the short assignment take over their boredom for the few minutes.

Anyway, there were some with near-accurate results, some with nowhere-accurate results.

Which brings me to my question (in a roundabout way):

Are you born with an innate ability to hear pitch differences, is it a learned action, or is it a matter of both? For me, I remember harmonizing with motors when I was really little...five or so. I, however, come from a musical family.

By contrast, I have known people with a very unmusical family and with very little musical enrichment who could not hear the difference between a harp and a trombone. And no amount of teaching them resulted in anything.

Then, I know of one girl who could not hear pitch at all, but after much training ended up being the soprano section leader in my concert choir.

I would really like to know whether pitch differentiation is genetic or learned. I figure, like most topics of similar discussion, it is a matter of both. It would make for a good case study, if it hasn't been done already. (If you know of a related case study, let me know.)