13 Human Choices
. . . there is no country in the world in which people are satisfied with having barely enough to
eat. —KINGSLEY DAVIS 1991
A little boy wanted to know the sum of one plus one. First he asked a physicist, who said, "If one
is matter, and the other is antimatter, then the answer is zero. But if one is a critical mass of
uranium and the other is a critical mass of uranium, then that's an explosive question."
Unenlightened, the little boy asked a biologist. She said, "Are we talking bacteria, mice or
whales? And for how long?" In desperation, the boy hired an accountant. The accountant peered
closely at the little boy and said, "Hmmm. One plus one? Tell me, little boy, how much do you
want one plus one to be?"
There were more dimensions to the question than the little boy had considered. In addition to the
pure mathematics, there were physical and biological constraints (the laws of matter and
antimatter, critical masses, bacteria, mice and whales). And there were choices (for how long?
and what do you want from one plus one?).
Estimating how many people the Earth can support requires more than demographic arithmetic.
Like calculating one plus one, it involves both natural constraints that humans cannot change and
do not fully understand, and human choices that are yet to be made by this and by future
generations. Therefore the question "How many people can the Earth support?" has no single
numerical answer, now or ever. Because the Earth's human carrying capacity is constrained by
facts of nature, human choices about the Earth's human carrying capacity are not entirely free,
and may have consequences that are not entirely predictable. Because of the important roles of
human choices, natural constraints and uncertainty, estimates of human carrying capacity cannot
aspire to be more than
ble estimates: if future choices are thus-and-so,
the human carrying capacity is
likely to be
so-and-so.No sharp line separates human choices and natural constraints. For example,
technology obeys the laws of physics, chemistry and biology, but humans choose how, and how
much, to invest in creating and applying technology. Hence, the technology that people use
depends jointly on human choices and natural constraints. In another example, how the human
body responds to chemicals is a natural constraint on health, but individual choices (about food,
smoking, alcohol and other drugs) and social and economic decisions (about the use of lead in
gasoline and paints, about the production and disposal of radioactive wastes) determine the
extent to which human bodies are exposed to chemicals.The fuzzy zone between choices and
constraints shifts as time passes. Changes in knowledge can reveal constraints that had not been
recognized previously, and can also make possible new choices.Further, a choice open to rich
people may be a constraint for poor people. People from rich countries who become infected
with malaria, tuberculosis or trachoma generally choose to get the infection specifically