Today, an old, but still useful, estimate of
Earth's carrying capacity. 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.
Demographer Joel Cohen says
it's again time to ask how many people Earth can
hold. As he weighs the question, he tells about an
ecologist, an economist, and a statistician who
went hunting deer with bows and arrows. The
ecologist loosed his arrow and it fell five yards
in front of the deer. The economist's arrow fell
five yards behind the deer. At that point the
statistician joyfully shouted, "We got it! We got
it!"
So if we say Earth can hold ten billion people with
20 percent of us living five yards ahead of the
starvation level and 80 percent of us one yard
behind it, that's pretty unsatisfactory.
Cohen quotes an estimate made in 1679 by the same
Antonie van Leeuwenhoek who built microscopes and
discovered germs. Leeuwenhoek applied Holland's
population density to the land area of Earth. (I
wonder if his germs made him think of doing that!)
The trouble is, 17th-century Holland was a wealthy
trading country served by thinly-populated
colonies. Leeuwenhoek estimated Earth could support
13.4 billion people, and we've already reached 5.7
billion. We're almost halfway there! And here's
another number to think about: If we were to keep
increasing Earth's population until the year 2150
at the 1990 rate of population increase, we'd reach
700 billion people. Of course we can't possibly
sustain that rate because nature will take
responsibility for reducing population if we don't.
Suppose, on the other hand, we immediately
convinced all the people in the world to parent
only the children needed to replace them when they
died. Earth's population would still keep
increasing as today's children produced children,
then grandchildren. It would level out at 8.4
billion by 2150 -- dangerously close to
Leeuwenhoek's estimate.
But how seriously should we take a 300-year-old
number? Other people made estimates during the 18th
century -- all close to Leeuwenhoek's. Then the
19th-century notion of progress took over. Surely
progress, abstract and undefined, would somehow
solve the problem! In this century, demographers
have said little about the question. They realize
by now that the number of people Earth can hold
will vary with the quality of their lives. The
highest population will be one that's constantly
eroded by famine and disease -- just as population
growth is already being eroded today.
So what does drive population? The Catholic Church
catches plenty of flak, but Catholic Spain and
Italy are tied for the lowest fertility rate in
Europe. The culprit isn't religion; it isn't race.
The two factors that consistently yield high
population growth are poverty and the denial of
education for women. Until we solve those problems,
we'll keep hurtling toward that 300-year-old --
doomsday number.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
