International Balzan Foundation Luigi Luca Cavalli

Luigi Luca Cavalli-Sforza
The study of evolution received a solid framework with the introduction of a
mathematical theory which was developed between 1918 and 1950 by three
great scientists, Sir Ronald A. Fisher, J. B. S. Haldane and Sewall Wright. From
1948 to 1950 I had the good fortune to work with Sir Ronald Fisher in Cambridge
and derived great benefit from the relationship. Soon after this, I found
myself asking the question as to whether it would be possible to reconstruct the
evolutionary history of man by analysing the genetic differences between humans
living today. At that time there were not yet sufficient genetic population
data. Knowledge was limited to the frequency distributions of certain blood
groups, including the so-called ABO system used for blood transfusions, and
the famous rhesus system, as well as a few others. So until enough additional scientific
knowledge could be collected to form a critical mass, the time could be
devoted to studying the theory of evolution. At that time, there were two fundamentally
different views as to the significance of the two major evolutionary
factors: natural selection, on the one hand, and on the other, the effects of
chance due to the limited size of populations. This inevitably leads to fluctuations
in the statistical frequency of occurrence of genetic characteristics, and
their effects would accumulate over generations.
There was absolutely no doubt that natural selection played a central role. The
influence of chance had already been especially investigated by one of the fathers
of the mathematical theory of evolution, Sewall Wright, but there were still
no usable empirical data. In passing, I am pleased to be able to remind you that
Sewall Wright was awarded the Balzan Prize in 1984, having outlived the other
two great scientists by a good many years. The other geneticist who has so far
had the honour of receiving this prize was John Maynard Smith, who was one of
the most brilliant students of J. B. S. Haldane. So we have the interesting coincidence
that of the three geneticists who have been awarded the Balzan Prize
until now, Sewall Wright was the last of the three great names who was still alive,
and the other two were students of Haldane and Fisher.
I set out to solve the problem of how to measure the effects of chance on genetic
variation by studying a population group in the neighbourhood of the University
of Parma where I was teaching in the nineteen-fifties. The idea was that
it should be easy to predict the effects of chance on the genetic differences between
the various villages, by using demographic data reconstructed on the basis
of church records of births, marriages and deaths going back to the year
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