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by Mildred Boyd
It
all began when, some 1.5 million years ago, seismic convulsions threw
up chains of mountains to form a catchment basin with only one outlet,
trapping the waters of the Lerma River to form the largest natural lake
in what would eventually become Mexico. Situated well below the Tropic
of Cancer at an altitude of nearly five thousand feet, this huge body
of water acts as a thermal flywheel to moderate both tropical heat and
high- altitude cold and creates an almost perfect environment for living
things. Plants and animals soon established themselves; birds haunted
the shoreline, fish teemed in the depths and mammals preyed on both for
countless millennia before man appeared on the scene.