pnas | How did human societies evolve from small groups, integrated by
face-to-face cooperation, to huge anonymous societies of today,
typically organized as states? Why is
there so much variation in the ability of different human populations to
construct viable
states? Existing theories are usually
formulated as verbal models and, as a result, do not yield sharply
defined, quantitative
predictions that could be unambiguously
tested with data. Here we develop a cultural evolutionary model that
predicts where
and when the largest-scale complex
societies arose in human history. The central premise of the model,
which we test, is that
costly institutions that enabled large
human groups to function without splitting up evolved as a result of
intense competition
between societies—primarily warfare.
Warfare intensity, in turn, depended on the spread of historically
attested military
technologies (e.g., chariots and cavalry)
and on geographic factors (e.g., rugged landscape). The model was
simulated within
a realistic landscape of the Afroeurasian
landmass and its predictions were tested against a large dataset
documenting the
spatiotemporal distribution of historical
large-scale societies in Afroeurasia between 1,500 BCE and 1,500 CE. The
model-predicted
pattern of spread of large-scale societies
was very similar to the observed one. Overall, the model explained 65%
of variance
in the data. An alternative model,
omitting the effect of diffusing military technologies, explained only
16% of variance.
Our results support theories that
emphasize the role of institutions in state-building and suggest a
possible explanation
why a long history of statehood is
positively correlated with political stability, institutional quality,
and income per capita. Fist tap Dale.
