BOOK REVIEW
A Master Synthesizer
Oren Harman
A Genetic and Cultural Odyssey: The Life and Work of L. Luca
Cavalli-Sforza. Linda Stone and Paul F. Lurquin. xiv + 227 pp.
Columbia University Press, 2005. $45.
A young man of 18, having hesitantly prepared his registration
documents for medical school, takes his place in line at the
university to hand them in. While waiting, he notices that the line
beside his is for registration in the natural sciences. Suddenly, an
exciting thought enters his mind: Perhaps I should switch lines! But
no, that would mean filling in an entire new set of registration
forms. Better to stay put.
The place was Turin, the time 1940. Eventually all of the students
at the university except those in medical school would be drafted to
fight in World War II. The young man's laziness would thus
prove to be a stroke of luck. His name? Luigi Cavalli—now L.
Luca Cavalli-Sforza. After medical school and a brilliant stint as a
bacterial geneticist, he would take up population genetics and
demonstrate the all-important role of chance in the evolution of
mankind. So despite his choice of lines in 1940, it would be in the
natural sciences rather than in medicine that he would make his
great contributions.
Now the first biography of this extraordinary man has appeared:
A Genetic and Cultural Odyssey, by anthropologist Linda
Stone and geneticist Paul F. Lurquin. It is most welcome.
Cavalli was born in Genoa in 1922. At age 20 he stopped calling
himself Luigi and at the suggestion of a mentor renamed himself
Luca. Then at age 27 he was officially adopted by his maternal
stepgrandfather, Count Francesco Sforza, and changed his name to Cavalli-Sforza.
In 1948 he met the great English statistician R. A. Fisher, who
offered him a job at the University of Cambridge applying
statistical methods to the study of the genetics of bacteria.
Cavalli-Sforza's involvement in figuring out bacterial conjugation
(how bacteria mate) has somehow been omitted from most histories,
but in fact he helped Joshua and Ethel Lederberg and William Hayes
crack this fundamental problem. At the time, a geneticist remarked
jocularly, "How can you believe this bacterial sex thing,
knowing that it was discovered by a Jew, an Italian, and an
Irishman!" But the evidence was incontrovertible: Bacteria do
sometimes engage in genetic recombination. This seminal scientific
discovery, Cavalli-Sforza's most important, opened up new avenues
for genetic and medical research and transformed molecular
biology—leading, among other things, to the operon model of
gene regulation proposed by François Jacob and Jacques Monod.
After a decade of work on bacteria, Cavalli-Sforza decided that
"humans are more charismatic than E. coli!" and
turned to the study of what would ultimately earn him international
fame: the genetics of human populations and its bearing on human
culture and history. He wanted to know why there are genetic
differences between populations of humans, such that a particular
blood type, for example, may be found more frequently in Alaskan
Eskimos than in the Blackfoot tribe of Native Americans. If all
humans have a common origin, how did these variations come to be, he
wondered. Could one study the factors responsible?
Honing his statistical skills, Cavalli-Sforza developed mathematical
tools to trace the contours and causes of genetic variation,
measured at first by diversity in human proteins and blood types,
and later, following the development of mitochondrial and
Y-chromosome techniques, by differences at the DNA level. These
methods enabled him to distinguish among the four factors that
traditionally influence gene frequencies in a population: natural
selection, migration (gene flow or admixture), gene mutation and
chance persistence of mutations that offer no selective advantage or
disadvantage (referred to as genetic drift). His models showed that
the last phenomenon played a crucial role in accounting for much of
human genetic diversity: For example, during certain transitions
(called "bottleneck events"), only a small proportion of a
population might survive to reproduce—not because this group
is necessarily more fit, but rather merely due to chance. The genes
of this particular chance group will then dominate the entire gene
pool of populations to come.
The role of drift is important. Deleterious or advantageous
mutations to the gene pool that are under the control of natural
selection (for example in genes for skin color, body size, hair
texture and the shape of the nose—traits that have been used
to categorize humans into races) can teach us a lot about the
history of the environmental challenges faced by different
populations of humans. But neutral or almost neutral mutations that
constitute drift are more useful in tracing the history of the
humans themselves because they are far more numerous. By showing
that the unseen genetic diversity within groups of people
is much greater than that which accounts for the clearly apparent
differences between them, Cavalli-Sforza's work has
constituted a scientific blow to the biological concept of race.
Sadly, as Stone and Lurquin show, this has not shielded
Cavalli-Sforza himself from unfounded accusations of racism.
Above all a master synthesizer, Cavalli-Sforza grasped that much of
human evolution—biological, cultural and linguistic—can
be illuminated by looking at how and where groups of humans have
migrated across the globe. When people move from place to place,
they take with them their genes, their diseases, their languages and
their culture. He understood that to unravel humankind's complex
movements out of Africa some 50,000 years ago and across the Earth
since, the usual divides between the social and natural sciences
would need to be felled—archaeological, linguistic, historical
and anthropological comparisons would have to be marshaled alongside
the genetic evidence.
Cutting across disciplines, Cavalli-Sforza met with much resistance:
from linguists, who challenged the assumptions behind the neat fit
he demonstrated between genetic and language maps of the world; from
biologists and mathematicians, who critiqued his genetic and
statistical techniques; and from cultural anthropologists, who
considered his quantitative models of cultural diffusion to be
oversimplifications based on naive analogies from genetic diffusion.
Some of Cavalli-Sforza's claims and models remain contested, and a
more detailed analysis of the criticisms would have been welcome in
this book, which was written, perhaps to a greater extent than it
should have been, under Cavalli-Sforza's guidance. (For a more
penetrating and hardheaded, albeit sympathetic, critique, readers
might want to consult John Maynard Smith's Did Darwin Get It
Right?, which contains an excellent review of Cavalli-Sforza
and Mark Feldman's models of cultural diffusion.) Nevertheless,
Stone and Lurquin do an excellent job of presenting Cavalli-Sforza's
impressive iconoclasm and awesome intellectual breadth.
They report that Cavalli-Sforza remembers once asking anthropologist
Claude Lévi-Strauss what he thought of cultural transmission
and receiving this answer: "It is too complicated to
study." Cavalli-Sforza chose to challenge that view. Theorizing
about culture by analogy to biological evolution may or may not
ultimately prove useful. But if we are ever to understand ourselves
and our history better than we do today, we must attempt to
integrate the traditionally separate compartments of human
knowledge. This fascinating little book demonstrates that
Cavalli-Sforza has blazed a path well worth following.