My dad is not a singer, but without any apparent effort, he can sing a harmony to just about any song. Broadway show tunes, TV commercials, "Midnight at the Oasis" — he hears it once and somehow knows where to add the layer of his voice. I've got that gene too, along with a pretty powerful desire to seek out others of my kind and stack the tones like an aural linzertorte. Why is this pleasurable? Why is the buzzy interaction of certain sounds so profoundly irresistible? And why does harmony make whatever you're singing seem all the more powerful? A good place to explore these questions is at the Sacred Harp sing held at the Ark nearly every month, on the second Sunday.

The sound of singing tumbled down the stairs and out into the street. In the Ark's small cafe area, chairs were set into four clusters — soprano, alto, tenor, bass — on each side of a square, facing in. There were perhaps fifteen people there on this chilly November afternoon, including a librarian, a massage therapist, a patent lawyer, and the Ark's own David Siglin. I was warmly welcomed, but I made it clear that I was practically a beginner. I found a pro to sit next to, opened up a red Sacred Harp book that someone handed me, and turned to p. 154.

First of all, no harps are plucked at a Sacred Harp sing. The Sacred Harp was a book, first published in 1844, filled with hundreds of four-part Christian hymns, odes, and anthems meant to be sung unaccompanied. The book has been updated through the years as new songs are added. There have always been stalwart Sacred Harp groups, largely in the South, but throughout the country as well, where people gather to sing, share meals, and sing again. Today, popularity of the form is on the rise; the movie Cold Mountain gave it a huge boost.

Sacred Harp songs are written in four "shape notes": "la" is a square, "fa" is a triangle, "sol" is a circle, and "mi" is a diamond. A scale sung using the shapes would go "fa, sol, la, fa, sol, la, mi, fa." When a particular hymn is called, the singers first sing it through using the shapes and then again with the words. If that sounds complicated, it is. The woman next to me whispered, "Don't worry about the shapes — just sing 'la' on everything if you want to." I did, and was right 25 percent of the time. It was a little easier with the words — so long as I didn't think about what I was singing.

This is dark stuff, penned during a time in which death was a part of daily life, earthly life was regarded as an uncomfortable way station to heaven, and faith explained everything, good and bad. Times are bad now too, I suppose, and there's comfort to be found in the more uplifting lyrics, but as I found myself loudly intoning things like "What is this that steals, that steals upon my frame? Is it death? Is it death?" my mind kept coming back to germ theory and antibiotics and the comforts therein. Songs like "World Unknown" ask, "Am I born to die? To lay this body down? And must my trembling spirit fly into a world unknown?" and made me realize afresh that there are some questions that are uniquely human, and asked across the ages.

We each had a chance to select our favorites. Someone would volunteer to stand in the center and lead the group, though I will confess I could not take my eye off the book long enough to be led by anyone. Some songs were slow and ponderous (I liked these best); others were so fast I just kept my mouth shut and slid my finger along the staffs, trying to figure out where we were. And through it all was the harmony I'd come looking for, rich and intoxicating. The ending notes were the best: powerful and resonant. All voice types were welcomed. Some folks sounded "trained," while others just sang in everyday voices. I've heard some recordings of Sacred Harp sings in the rural South and noticed a peculiar nasal stridency that is both compelling and scary. The Ark group has a gentler sound.

Through it all, a seven-month-old named Carl sat on the floor by his mom and played with toys. Three hours is a long time to be a baby at a Sacred Harp sing. But when Carl made his presence known, during a morose minor-key plaint, he was right on pitch.