These questions come to mind during this year's "Past/Forward" program, running through tonight in Reynolds Theater at Duke as part of the American Dance Festival. This fascinating journey through modern dance history illuminates three distinct eras with three distinctive works: Helen Tamiris' "How Long Brethren?" from 1937, Laura Dean's "Sky Light" from 1982 and Rudy Perez' "I Like a View But I Like to Sit With My Back to It," commissioned by ADF and premiering this week.

Presenting seminal works from the past is an important educational function of ADF, but experiencing firsthand the earthy, flesh-and-blood style of Tamiris is anything but an academic exercise. With evocative vocal interludes by Mavis Kashanda Poole and Ariane Reinhart supplementing historic recordings of Negro spirituals, the performance transports you to a time, a place and a feeling that no history book could conjure.

This reconstruction by acclaimed choreographer/teacher Dianne McIntyre places ADF's student performers into the history of their art. They feel a certain moment in the development of a style, immerse themselves in the period that gave rise to it and bring it to life for us. In turn, we see familiar movements, gestures and postures, and we understand how pioneers like Tamiris broke ground and forged building blocks for generations to come.

You can't see the final, haunting image -- a train of interlocked female bodies silently chugging into the wings as the curtain falls -- and not think Tamiris is as much a part of today as yesterday.

It's curious -- and telling? -- that Perez's new work shares a certain darkness with Tamiris' Depression Era classic.

With a soundscape by Michael Wall that whines, whirs and buzzes when it doesn't completely fall silent, Perez draws fluently from a full range of styles. While there are softening touches of balletic movement (jetes, arabesques), a harsh undertow derives more from the athletic (flat-footed leaps straight up) and the acrobatic (floor dives, even head stands). Not to ascribe too much, but you feel a muted anger -- in repetitions, in frustrated outbursts -- that belongs to the past seven years.

What a release, then, to return to the early '80s -- the Reagan era, Rubik's Cube, Morning in America, "Dallas." This was the moment in which Laura Dean Dancers and Musicians made their mark with high-energy experiments like "Sky Light," staged here by Rodger Belman.

With a percussion score expertly re-created by Jason Cirker and Matt Spataro, the dancers revel in rays of sun with a spirit as bright as the yellow costumes they wear. With neither breaks nor pauses for 30 minutes, they mesmerize you with tireless variations of arcing leaps and ritualistic gestures, culminating in a dizzying spinning contest at centerstage.

These inspiring dancers -- Andrew Chaplin, Domingo Estrada Jr., Hsiao-Jung Huan, Meghan Milam, Matthew Reeves and Hsiao Tzu Tien -- transmit their own light. They make you want to move; they make you want to live.