Introduction Box 1 Human population and conservation
Paul R. Ehrlich
The size of the human population is
approaching 7 billion people, and its most
fundamental connection with conservation is
simple: people compete with other animals,
which unlike green plants cannot make their
own food. At present Homo sapiens uses,
coopts, or destroys close to half of all the food
available to the rest of the animal kingdom (see
Introduction Box 1 Figure). That means that, in
essence, every human being added to the
population means fewer individuals can be
supported in the remaining fauna.
But human population growth does much
more than simply cause a proportional decline
in animal biodiversity – since as you know, we
degrade nature in many ways besides
competing with animals for food. Each
additional person will have a disproportionate
negative impact on biodiversity in general. The
first farmers started farming the richest soils
they could find and utilized the richest and most
accessible resources first (Ehrlich and Ehrlich
2005). Now much of the soil that people first
farmed has been eroded away or paved over,
and agriculturalists increasingly are forced to
turn to marginal land to grow more food.
Equally, deeper and poorer ore deposits must be
mined and smelted today, water and petroleum
must come from lower quality sources, deeper
wells, or (for oil) from deep beneath the ocean
and must be transported over longer distances,
all at ever‐greater environmental cost.
The tasks of conservation biologists are made
more difficult by human population growth, as
is readily seen in the I=PAT equation (Holdren
and Ehrlich 1974; Ehrlich and Ehrlich 1981).
Impact (I) on biodiversity is not only a result of
population size (P), but of that size multiplied
by affluence (A) measured as per capita
consumption, and that product multiplied by
another factor (T), which summarizes the
technologies and socio‐political‐economic
arrangements to service that consumption.
More people surrounding a rainforest reserve
in a poor nation often means more individuals
invading the reserve to gather firewood or
bush meat. More people in a rich country may
mean more off‐road vehicles (ORVs) assaulting
the biota – especially if the ORV manufacturers
are politically powerful and can successfully
fight bans on their use. As poor countries’
populations grow and segments of them
become more affluent, demand rises for meat
and automobiles, with domesticated animals
continues