International Balzan Foundation Luigi Luca Cavalli

Luigi Luca Cavalli-Sforza
and wanted to get to see the Atlantic Ocean. I did not ask why, but I can understand
them: I, too, am motivated by very strong curiosity. However, the move
from food gathering to food production, which started in very distant places at
around the same times, about ten thousand years ago, brought about an almost
exponential growth in population to a thousandfold increase which is now nearing
its limits. Are we ready for a new crisis: expansion outside Earth, self-destruction?
The spread of agriculture from its place of origin was very slow. P. Menozzi, A.
Piazza and I have been able to calculate its rate fairly exactly in Europe, and it
was possible to explain it by the combination of two demographic phenomena,
growth and emigration, to generate population expansion from the area of origin.
Population growth was made possible by the increased availability of food,
and as soon as it reached a new level of saturation it caused geographic expansion
by migration, mostly of family groups or small social nuclei, to neighbouring
areas offering potentially fertile soil. In research in collaboration with archaeologist
Albert Ammerman, we suggested the name of demic diffusion for
this process. It took some time to have this hypothesis accepted by archaeologists,
especially in northern Europe and the USA, because it was totally opposite
to the trend of thought that had developed there, in opposition to ideas popular
in the nineteen-twenties. Clarke, who was mostly responsible for these ideas, explained
every archaeological variation by the movement of people. When, after
the war, the pendulum swung to the opposite pole, the hypothesis of migration
disappeared. Only traders moved, carrying with them products that have been
found and used by archaeologists to describe such expansions : a fashion now
called indigenism. But the idea that it was really the growth and migration of
farmers who brought farming around the nuclear area has been tested by showing
that there are gradients of genes of Middle Eastern origin across Europe,
which follow rather precisely the archaeological paths of the penetration of
farming. Dates and rates of expansion are also in agreement with genetic and
demographic calculations. The observed genetic gradient could have formed
only if, in addition to the demic diffusion of farmers, there was adoption of
farming by local hunter-gatherers, either by marriage or by acculturation.
Cosmologists and astronomers are also afflicted by the problem of the history of
the world being unable to be repeated. One advantage they have is that they can
make much more precise measurements of their observations, and theoretical
predictions to test their hypotheses. Biology is beginning to follow this example.
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