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Demic Versus Cultur al Diffusion
There are two contrasting views on the mechanism by which agriculture spread to Europe: by
the physical migration of people, sometimes referred to as demic diffusion, or by informa-
tion transfer, or cultural diffusion. The demic diffusion model can be traced back to the
renowned Australian archaeologist and philologist V. Gordon Childe who first introduced
the term “agricultural revolution” in 1935. According to Childe’s hypothesis, agriculture
led to increases in population in the Near East, and it was this population pressure that led
to the migration of people to the less densely populated areas of Europe, using the Balkan
Peninsula as a “bridge” to Europe.^10 These Neolithic people brought their agricultural way
of life with them.
The demic diffusion model is supported by two main lines of evidence: archaeologi-
cal and genetic. The archaeological evidence is based on radiocarbon dating of the ages of
European Neolithic sites. When these dates are assembled on a map together with dates
for the original Neolithic settlements in the Near East, a clear gradient is evident from the
oldest sites in the Near East to the most recent sites along the northwest coast and Britain.
However, such a gradient would be expected whether agriculture spread by demic or cul-
tural diffusion.
The genetic evidence for demic diffusion is based on a comparable east– west gradient in
gene frequencies (i.e., the frequency of occurrence of particular versions of certain genes)
among populations of Europeans today. Such a genetic gradient could only be established
by the physical migration and mixing of human populations. Accordingly, population
geneticist Luigi Luca Cavalli- Sforza and his colleagues, who first discovered the genetic gra-
dient, attributed it to successive waves of expansion of populations out of the Near East that
occurred during the Neolithic period.^11 It has been estimated that as little as a 10% increase
in dietary intake due to agriculture can cause a 50% rise in population size, which could
be a significant driver of migration.^12 However, others have suggested that the east– west
genetic gradient actually reflects movements of people that took place much earlier, during
the Paleolithic period.
In recent years, greater attention has focused on the role of cultural diffusion, that is, the
adoption of farming and animal husbandry by indigenous foraging societies without their
being assimilated by an outside group. The importance of cultural diffusion in the spread
of agriculture is consistent with recent analyses of mitochondrial DNA. Although an east–
west gradient in mitochondrial DNA sequences was confirmed, it could only account, on
average, for about 13% of the total variability observed.^13 In agreement with this more mod-
est assessment of the amount of genetic mixing that took place as agriculture spread to
Europe, Cavalli- Sforza has pointed out that the east– west genetic gradient he identified
only accounted for about 25% of the total genetic variability. In other words, both molecular
and genetic studies agree that although demic diffusion probably occurred, the number of
Neolithic colonists who spread out from the Near East did not exceed about 20% of the
indigenous populations.
Despite the evidence against large- scale migration of Neolithic farmers from the Near
East into Europe, colonies of Neolithic migrants were probably crucial to the spread of
agriculture. Because writing had not yet been invented, it is difficult to conceive how such
a thorough transformation in lifestyle could have been brought about by word of mouth