things combine to produce this result. Chief among them are
malaria and other tropical diseases. When a few miles of railroad
were being built through a strip of tropical forest along the
coast of eastern Guatemala, it was impossible to keep the
laborers more than twenty days at a time; indeed, unless they
were sent away at the end of three weeks, they were almost sure
to be stricken with virulent malarial fevers from which many
died. An equally potent enemy of agriculture is the vegetation
itself. Imagine the difficulty of cultivating a garden in a place
where the weeds grow all the time and where many of them reach a
height of ten or twenty feet in a single year. Perhaps there are
people in the world who might cultivate such a region and raise
marvelous crops, but they are not the indolent people of tropical
America; and it is in fact doubtful whether any kind of people
could live permanently in the tropical forest and retain energy
enough to carry on cultivation. Nowhere in the world is there
such steady, damp heat as in these shadowy, windless depths far
below the lofty tops of the rain forest. Nowhere is there greater
disinclination to work than among the people who dwell in this
region. Consequently in the vast rain forests of the Amazon basin
and in similar small forests as far north as Central America,
there are today practically no inhabitants except a mere handful
of the poorest and most degraded people in the world. Yet in
ancient times the northern border of the rain forest was the seat
of America's most advanced civilization. The explanation of this
contradiction will appear later.*

* See Chapter 5, Aztecs.