In her recent The Watchman's Rattle, subtitled Thinking Our Way Out of Extinction, Rebecca Costa delivers a fascinating account of how civilizations die.

Their problems become too complex.

Societies reach what she calls a cognitive threshold.

They simply can't chart a path from the present to the future. The example she gives is

of the Mayans. For a period of three and a half thousand years between 2,600 BCE and 900 CE,

they developed an extraordinary civilization, spreading over what today is Mexico, Guatemala,

Honduras, El Salvador and Belize,

with an estimated population in those days of 15 million people. Not only were they

master potters, weavers, architects and farmers, they developed an intricate cylindrical calendar

system with celestial chance to track the movements of the stars and predict

weather patterns. They had their own unique form of writing, as well as an advanced mathematical

system. Most impressively, they developed a water supply infrastructure, involving a complex

network of reservoirs, canals, dams and lavasse.

Then suddenly, for reasons we don't still fully understand, the entire system collapsed.

Sometime between the middle of the 8th and 9th century, the majority of the Mayan people

simply disappeared. There have been many theories as to why it happened. It may have been prolonged

drought, overpopulation, interneesign wars, a devastating epidemic, food shortages, or a combination

of these and other factors. One way or another, having survived for 35 centuries, Mayan

civilization failed and became extinct.

Rebecca Costa's argument is that whatever the causes of the Mayan collapse, it like the fall of the

Roman Empire and the fall of the Khmer Empire of 13th century Cambodia happened because problems

just became too many and complicated for people of that

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