Today, the advantage of being horizontal. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
Consider an odd fact you may
not've noticed. It is that, of the four large
continents, only one runs east and west. It's the
largest one, Eurasia, formed by Europe and Asia.
Eurasia is nine thousand miles wide. Both the
Americas and Africa run north and south.
Biologist Jared Diamond looks at that fact and
reminds us that climate largely follows latitude,
not longitude. Eurasia is not only the largest of
the continents, but it's the only one where you can
travel more than three thousand miles without
encountering radical changes in the general
That fact has determined the nature of life on
those continents. For example, the llama never
found its way from South America into Central
America, nor did the bison move south beyond the
present-day United States. Mexican corn couldn't grow in
In Eurasia, horses and cattle spread to both Spain
and China. After agriculture
arose in the Middle East, ten thousand years
ago, it spread methodically eastward and westward.
Not only did domestic plants have lands to move
into; the people who grew them also followed the
climates they'd learned to tolerate.
That spread didn't strictly follow lines of
latitude, but it zigged slightly to accommodate
climatic variations. Agriculture followed a path
through the Balkans and
diagonally across Europe until it reached the
temperate parts of Ireland
around 3000 BC.
The humans who used domesticated animals and
agriculture were part and parcel of those
technologies. As we moved with our animals and
agriculture, our technologies followed. Two
particular technologies, virtually unknown in
Africa or the Americas, spread laterally in
Eurasia. They were writing and the wheel.
The wheel, invented fifty-five hundred years ago at
the northern end of the fertile crescent, diffused
rapidly across Eurasia. Ancient Mexicans thought of
the wheel, but since agriculture didn't move north
or south, neither did the wheel. It died in
Writing, invented fifty-two hundred years ago in
Egypt , traveled rapidly throughout Eurasia and
across North Africa, but not downward into
sub-Saharan Africa. Writing also arose in Central
America, but, like the wheel, it stayed there.
So agriculture and domesticated animals came late to
the other three large continents, and, once there,
they stayed horizontally stratified. Diamond's
radical suggestion is that the lateral diffusion of
agriculture in Eurasia jump-started all its
Long ago, Daniel Webster had a visceral
understanding of this process. In 1840, just before
he became Secretary of State, he wrote,
When tillage begins, other arts follow.
The farmers therefore are the founders of
Now Diamond suggests that early inhabitants were
able to give full expression to that natural
kinship of agriculture and technology on only one
continent -- only in horizontal Eurasia.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds