For a century or so, the decline and fall of Maya cities in the jungles of Mexico, Guatemala and Honduras was an enigma. Recent work in the ancient city of Copan and other sites, however, has shown the Maya collapse was caused by overpopulation and depletion of natural resources. The evidence is found in forensic examination of human skeletons which reveals the unmistakable stress of malnourishment and from excavations showing erosion of once fertile soil from nearby hillsides due to over farming. In the 8th century AD, 25,000 people lived in Copan. Then, within a hundred years or so, the population declined and the once thriving city began to melt into the jungle. Analysis of ancient pollen shows that by about 1200 AD a forest had grown up where fields were once tilled.

On Easter Island, similar research shows a steady rise in population followed by a rapid decline and an abrupt end to the carving of those great enigmatic statues - the Moai. One such statue, the grandest of all by far (65 feet tall and weighing 270 tons) lies half finished in a quarry - as if the islanders had thrown down their tools and walked away in a single day.

And at Sand Canyon Pueblo in Colorado, archeologists have discovered that houses were burned prior to a rapid abandonment of the city. In the charred remains they discovered the bodies of Anasazi residents who had met a violent death.

Warfare - presumably over scarce food resources - accompanied the demise of all these cultures. In Easter Island and among the Anasazi there's also evidence of cannibalism in the last years.

I learned these facts because I made a series of PBS films about the subject some years ago.

Copan's archeologists do not believe the Maya saw the end coming. The population decline would have been slow at first - a few more babies expiring at birth and an earlier demise for the elders. This trend might have lasted - increasing only slightly - over a few generations. Then came a more rapid acceleration of the death rate. Then warfare.

The archeologists believe these earlier people may have suffered from a universal human condition - it is the nature of Homo Sapiens to be short sighted. At best, we seem able to extend our vision a generation or so into the future.

The more I see what's going on today - the more I believe that generalization.

Modern science allows us to monitor our environment in ways earlier civilizations could not. According to some estimates, for example, human societies today use 130,000 barrels of oil every minute to power our cars, air conditioners and warplanes. In America alone, we use 20,000,000 barrels daily. The burning of so much fuel creates a blanket of pollution that causes our earth to retain heat and may reasonably lead to increased sea levels and droughts. Acid rain pollutes our ponds and oceans. Some scientists predict that known oil reserves will be depleted within the next 20 years or so.

The Maya, looking out over their eroding fields, may be forgiven their failure to understand the fate that awaited them. Mayan scientists elevated their eyes to the stars to create a sophisticated calendar and divine messages from the gods. And from a planetary perspective, the demise of Maya civilization was a tiny event because their feeble agricultural technology damaged only a small portion of Earth. But today, we have evolved to a point where we are equipped to irrevocably damage the world we live in. We are also better equipped to see the end coming.

The question remains - will we be long sighted enough to do something about it - or will the same human flaw that led to the destruction of earlier societies prove fatal to our own as well?