More than 200 years ago Benjamin Franklin coined the now famous dictum that equated passing minutes and hours with shillings and pounds. The new millennium--and the decades leading up to it--has given his words their real meaning. Time has become to the 21st century what fossil fuels and precious metals were to previous epochs. Constantly measured and priced, this vital raw material continues to spur the growth of economies built on a foundation of terabytes and gigabits per second.

This reduction of time to money may extend Franklin's observation to an absurd extreme. But the commodification of time is genuine--and results from a radical alteration in how we view the passage of events. Our fundamental human drives have not changed from the Paleolithic era, hundreds of thousands of years ago. Much of what we are about centers on the same impulses to eat, procreate, fight or flee that motivated Fred Flintstone. Despite the constancy of these primal urges, human culture has experienced upheaval after upheaval in the period since our hunter-gatherer forebears roamed the savannas. Perhaps the most profound change in the long transition from Stone Age to information age revolves around our subjective experience of time.

But what is time? Physicists and philosophers have grappled with the question. So, too, have biologists and anthropologists. This special issue explores their musings. --The Editors