We will call these rhythms, which dominate the history of the later Agrarian
era, “Malthusian cycles.” Thomas Malthus was one of the pioneers of
modern demography. He argued that in all species, populations tend to grow
geometrically while resources tend to grow arithmetically. Eventually, this
means that population growth is bound to outstrip the available resources,
leading to disease, famine, and demographic collapse. Economic historian
Robert Lopez describes these cycles as “an alternation of crest, trough and
crest ... [that] can be observed not only in the economic ¿ eld, but in almost
every aspect of life” (Christian, Maps of Time, p. 309). As French historian
Le Roy Ladurie puts it, these cycles were like the “respiration,” the in-breaths
and out-breaths, of an entire social structure (Christian, Maps of Time, p.
309). Explaining these cycles takes us to the heart of the issue of innovation
in Agrarian civilizations. There was plenty of innovation in this era, but it
was never rapid enough to
keep pace with population
growth. This fundamental
fact explains the persistence
of Malthusian cycles over
several millennia despite a
long term tendency toward
growth throughout the later
Agrarian era.
We have seen that in the
later Agrarian era many of
the factors that stimulated
growth in some ways could
also inhibit or help to stiÀ e
growth and innovation. This balance of forces that encouraged and stiÀ ed
growth explains why, eventually, each phase of expansion ended in collapse.
In the last three lectures we have concentrated on Afro-Eurasia. But how
typical was the history of the Afro-Eurasian zone of humanity as a whole?
To answer that question we shift our focus to the Australasian, Paci¿ c, and
American world zones and ask what was happening there. Ŷ
Rameses, Egyptian ruler for much of the 13th
century, built this tomb, Ramesseum, for
himself outside of Thebes.Corel Stock Photo Library.