I was throwing rocks at the
Limits to Growth
partly because it assumed that human
beings have no ability to foresee or adapt to situations, which I at least hope is an
unnecessarily gloomy view of human capacity, and partly because it was based on a state
description involving five variables only.
I want to start today by recalling some of the relevant
variables, a number that will be far greater than five.
On the side of population alone, what do
we have so far?
These include the size of the population; age; gender profile and particularly
the number of fertile women; the fertility rates of these women, as they change through time;
the ratio of girl-boy births; mortality rates among girls under the age of reproduction; childbed
mortality rate; mortality rates and longevity generally.
There are also variables relating to
changing population distribution, including population density among countries and within
many fewer people per square mile in Wyoming than Ohio
and also migration
issues, including internal migration or urbanization and migration from one part of the world
to another, as we
ll see next week.
Similarly, mortality and mortality rates are unequally
distributed around the world, as we
ll see when we discuss the AIDS epidemic and famine.
s also the question, if it is one, of whether people are actually dumber than
baboons, or whether they have the ability to adapt to changing circumstances and so to control
their own destiny, at least in part.
ll see today, government policies can very strongly
affect fertility rates.
It can do so both directly, most notably in the case of China but in many
other countries as well, as we
It can also do so indirectly through its agricultural policy.
For example, a policy that increases farm productivity per worker may encourage some
workers to leave the farm and become city dwellers, with concomitant impacts on fertility
The question is, how can you ever hope to quantify the effect of government policy so
you can use it as a variable?
t think you can.
The one-child policy had a major impact
on the population of China, so leaving it out seems sort of ridiculous, but
how can you
predict what the policy of the government is going to be or how it may change?
s one-child policy is not one thing but has changed over time, and its effects changed
over time as well.
How can you hope to predict all this and put it in a system model?
t either omit it or include it, maybe the moral is that system models of human
population are inherently flawed.
Fertility shifts: Economic or cultural causes?
I want to start with the second half of the demographic transition, the decreasing rate
of fertility, or what we
ve been calling Phase 3.
The demographic transition is marked by the
change from the high fertility rates of traditional society to the low fertility rates characteristic
of modern society.
The curve was first described in the 1920s, and the reason that fertility fell