These are ghostly clues, reminders that great cultures once flourished in the forests and islands of Central America and the Caribbean. They were called the Maya, the Taino, and the Aztecs. The story of how their worlds came to be -- and, eventually, not to be -- is told in NATURE's four-part special SPIRITS OF THE JAGUAR.

Over the course of four hours, SPIRITS OF THE JAGUAR takes viewers on a remarkable tour of the people and wildlife of the thin crescent of land and islands that links the great continents of North and South America. It shows how plants, animals, and people have swept back and forth along this narrow natural highway, producing a vibrant landscape full of cultural and biological treasures.

Perhaps no animal better symbolizes both the natural and human history of the region than the jaguar -- the great spotted cat that prowls its hillsides and valleys, an animal venerated as a god by early inhabitants. Like Central America's people, however, who arrived in that area just 30,000 years ago, the jaguar is an import: it came to Central America eons ago from Asia, and now resides only in the New World. And, like its human neighbors, the jaguar had to learn new ways of living in order to thrive. For instance, unlike most large cats, the jaguar is an excellent swimmer. Indeed, the cat appears to love water and prefers to live near rivers, where it feeds on aquatic rodents, turtles, and even crocodiles.

In contrast, the forerunners of modern jaguars headed east, eventually creeping across the land bridge that once spanned the Bering Strait and connected Asia and North America. These jaguar ancestors then moved south into Central America, feeding on the deer and other grazing animals that once covered the landscape in huge herds.

Climate changes, however, eventually wiped out the grazing herds and favored other animals, such as land tortoises and aquatic turtles. Some scientists believe the jaguar adapted to the change by developing the massive head and powerful, thick-toothed jaws capable of easily cracking open these well-armored animals. Somewhere along the way, the jaguar also lost its throaty, bone-shaking cry for a deep, guttural growl, making it the only big cat without a roar. Scientists aren't sure why that is, but it may be that a roar -- useful for communicating on wide-open desert plains -- isn't very useful in the sound-muffling foliage of tropical forests.

Jaguars typically kill with a crushing bite to the neck or a single deadly blow from a paw. And they can hunt at night, ambushing their prey with a ferocity that both impressed and terrified the region's ancient inhabitants, particularly since humans themselves occasionally were subject to the surprise attacks. The black jaguar, a color variant that is virtually invisible at night, instilled the greatest terror.

Like the Mayan and Aztec chieftains who once worshipped the spirit of the jaguar, however, the cat is also in danger of becoming a distant memory. Hunting and the clearing of its forest home for farms has made the jaguar an endangered species, reduced to living in a fraction of its historic range.

In these as-yet unspoiled forest enclaves, the spirit of the jaguar remains alive, as vibrant as the remarkable, vanished civilizations that once transformed simple stone into art for the ages and created cities and monuments that still have no equal.