Luigi Luca Cavalli-Sforza (1922–2018)

Luigi Luca Cavalli-Sforza (1922–2018) was a researcher whose work explored the relationships between human genetic diversity and historical migrations, integrating genetics and anthropology to determine how humans populated the world. Prior to his work in human genetics, Cavalli-Sforza studied genetic recombination in bacteria and helped determine the system of genetic inheritance within Escherichia coli in the late 1940s. After pivoting his research focus and assuming a long-term teaching and research position at Stanford University in Stanford, California, in 1971, Cavalli-Sforza participated in studies that modeled human migration, focusing on the global spread of agriculture during the Neolithic period. He was also one of the founders in the creation of the Human Genome Diversity Project, or HGDP, an international scientific collaboration launched in the early 1990s to map the genetic diversity of human populations across the globe. Cavalli-Sforza’s interdisciplinary approach to studying human history and human evolution left its mark on the fields of both genetics and anthropology in the twentieth and twenty-first centuries.

1. Early Life and Education
2. Work in Bacterial Genetics
3. Studies of Genetic Drift in Pavia, Italy
4. Research at Stanford University
5. Human Genome Diversity Project
6. Legacy and Impact

Early Life and Education

Cavalli-Sforza was born on 25 January 1922 in Genoa, Italy, as the only child of Attilia Manacorda and Pio Cavalli. His name was legally Luigi Renato Maria Cavalli, but his family called him Luca, a compound of Luigi and Cavalli. Cavalli-Sforza used the nickname for his professional and personal life. His father was an advertising agent who traveled extensively between Genoa, Italy, and New York City, New York. According to a memoir by geneticist A. W. F. Edwards, Cavalli-Sforza’s mother hailed from a distinguished family. She was among the first women in Italy to graduate from the University of Turin in Turin, Italy, with a degree in the humanities.

In 1926, when Cavalli-Sforza was four years old, his family settled in Turin, Italy. Cavalli-Sforza attended local public schools during his childhood and early teenage years. The curricula included Latin, classical Greek, French, English, and German. Upon entering high school, according to Edwards, Cavalli-Sforza disliked the limited academic curriculum the Fascist regime enforced at that time. With his family’s support, Cavalli-Sforza stopped attending school. He took the cumulative exam to pass high school as a private student when he was sixteen years old after independently studying for a year. Cavalli-Sforza was one of the youngest students to pass the exam at that time, and he also achieved the highest marks in the city of Turin. As an adolescent, Cavalli-Sforza traveled to foreign academic institutions, such as the University of Exeter in Exeter, England, where he learned new ideas about democracy.

In 1938, at age sixteen, Cavalli-Sforza began his undergraduate studies in medicine at the University of Turin in Turin, Italy. After a year, he transferred to the University of Pavia in Pavia, Italy, where he published his first paper on quantitative measurements of bacterial virulence at age twenty. Cavalli-Sforza received his undergraduate medical degree in 1944 at age twenty-two. At that time, he had authored eleven research articles. In his biography, he admits being embarrassed about his lack of practical medical experience due to his focus on research in the preceding years.

From 1944 to 1945, Cavalli-Sforza worked as a physician in Italy. He later described the experience as “really more a job for a priest” in a 2006 video interview. Cavalli-Sforza asserts that his experience prompted him to transition from clinical medicine toward research in microbiology and genetics. During the 1940s, medicine was less developed, and pharmaceuticals like antibiotics were largely unavailable.

In 1945, Cavalli-Sforza officially pivoted careers and began working as a researcher in the immunology laboratory of the Istituto Sieroterapico Milanese, a pharmaceutical research institute in Milan, Italy. There, he studied the bacterium E. coli. In 1946, Cavalli-Sforza married Alba Ramazzotti, a niece of one of his medical school professors. They remained married for more than sixty years, during which they raised three sons, Matteo, Francesco, and Luca Tommaso, and one daughter, Violetta.

Work in Bacterial Genetics

In July 1948, Cavalli-Sforza traveled to Stockholm, Sweden, for the Eighth International Congress of Genetics. He presented his conference paper titled “Bacterial Mutations for Resistance to Radiations and to Nitrogen Mustard.” At the event, Cavalli-Sforza introduced himself to Ronald Fisher, a statistician and geneticist. At that time, Fisher studied the mechanisms behind crossing over. Crossing over is the exchange of DNA between a pair of homologous chromosomes, with one from each parent, that share the same genes, which occurs during the development of egg and sperm cells. Fisher had been working on deriving a statistical model for DNA crossing over in experiments using mice. He also sought to explore that mechanism in bacteria due to recent work by Joshua Lederberg, a US-based scientist studying molecular biology. In 1946, Lederberg found that bacteria undergo recombination with each other. After a five-minute conversation at the conference, Fisher offered Cavalli-Sforza a position in his department at the University of Cambridge in Cambridge, England, to establish a laboratory focused on studying genetic crossing-over in bacteria.

In October 1948, Cavalli-Sforza assumed his position at Cambridge. He worked on multiple projects in which he applied statistical methods to the study of bacterial genetics. Lederberg sent him the E. coli strain he had used for his recombination experiments. Cavalli-Sforza isolated a mutant that exhibited a significantly higher frequency of recombination when he selected for mutations for resistance to nitrogen mustard. He reports that the study shows that the mutant increases genetic diversity, or the variety of genetic traits in a population. Cavalli-Sforza lectured on microbial genetics at Cambridge from 1948 to 1950 alongside his research. He left Cambridge in 1950 for the Istituto Sieroterapico Milanese.

During the next few years in Italy, Cavalli-Sforza continued his work on bacterial recombination in E. coli. In 1950, he was promoted to director of research for the Instituto Sieroterapico Milanese, a position he maintained until 1957. Cavalli-Sforza collaborated with Lederberg and his wife, Esther Lederberg, a scientist who also worked in bacterial genetics. Together, the three scientists delineated the F-system of sexuality in E. coli. The F-system refers to the functioning of the F plasmid, also called the fertility factor or sex factor. The F plasmid is a small piece of DNA that allows conjugation, or when a bacterium transfers genetic material to another bacterium. This process enables what researchers colloquially describe as bacterial sex. Cavalli-Sforza and the Lederbergs published their results in “Sex Compatibility in Escherichia Coli” in 1952 and “An Infective Factor Controlling Sex Compatibility in Bacterium Coli” in 1953. According to Edwards, Cavalli-Sforza asserted those efforts were his best contributions to bacterial genetics and his first important research.

Studies of Genetic Drift in Pavia, Italy

As Cavalli-Sforza describes in his biography, he began to feel unfulfilled with his position at the Instituto Sieroterapico Milanese. The laboratory emphasized the development of pharmaceutical products, in which Cavalli-Sforza had very little interest. In 1951, Cavalli-Sforza assumed part-time lecturing positions at the University of Parma in Parma, Italy, and the University of Pavia, where he taught genetics and statistics. In 1951, Antonio Moroni, a local priest and one of Cavalli-Sforza’s students at the University of Parma, showed Cavalli-Sforza parish books. In those books, the Catholic Church had recorded births, marriages, and deaths since the sixteenth century. According to Edwards, Cavalli-Sforza realized that long-term data could help analyze genetic trends in human communities, particularly in regard to the concept of genetic drift. Genetic drift is a mechanism of evolution. It involves random fluctuations in the frequency of a particular version of a gene in a small population that tends to reduce overall genetic diversity. Some versions of a gene are lost just by chance, and some increase to 100 percent frequency.

Cavalli-Sforza used the parish books to construct a complete genealogy of the inhabitants of Riana, Italy. The mountainous hamlet surrounding Parma, Italy, had a population of approximately 150 people in 1951. Cavalli-Sforza noted the presence of consanguineous marriages, or marriages between relatives, within his genealogy. In 1955, Cavalli-Sforza also collected blood samples from people who lived in villages in the Parma region, both in the mountains and the valley. Populations were smaller, and consanguineous marriages were more common in the mountains. In contrast, populations were larger, and consanguineous marriages were less common in the valley. Cavalli-Sforza recorded the blood type of each sample. He determined that the genetic variation of blood types was greater among villages in the mountains than among those in the valley.

He explained that the increased genetic variation among mountainous villages was likely related to genetic drift. There, the frequencies of each blood type allele, or a variation of a gene, varied significantly from one population to the next. Random fluctuations in alleles that occur in small populations caused that trend. In the less isolated valley populations with fewer consanguineous marriages, the frequencies of each blood type allele were more similar from one population to the next.

Cavalli-Sforza needed to determine if the genetic variation among the towns deviated from a mathematical model called Hardy-Weinberg equilibrium to confirm the occurrence of genetic drift. Hardy-Weinberg equilibrium is a principle in population genetics. It describes a state in which gene frequencies in a population remain constant from one generation to the next. In 1963, Cavalli-Sforza, Moroni, and their colleague Gianna Zei determined the expected genetic variation within the villages. They used a computer simulation that considered twenty-two villages with a total of 5,000 people. The researchers used probabilities derived from the observed blood group frequencies in the total population to assign each person a blood type. They stimulated a model in which there was no genetic variation among villages. Cavalli-Sforza and his colleagues ran the simulation with a time step of 10 years and parameter values obtained from the genealogy from the parish books. The genealogy included variables like the probabilities of marriage, reproduction, and death based on the age of each person and the geography of the town where they resided. The simulation correctly reproduced the observed genetic variations among villages. Cavalli-Sforza concluded that genetic drift significantly affected human evolution in those areas, a perspective that most geneticists at that time largely dismissed.

In 1960, Cavalli-Sforza left the field of bacterial genetics to focus solely on human population genetics. He quipped that humans are more charismatic than E. coli. From 1960 to 1963, Cavalli-Sforza worked full-time as a professor of genetics at the University of Parma. He then transferred to the University of Pavia in 1962, where he founded the Institute of Genetics. At the same time, Cavalli-Sforza participated in multiple research expeditions to Africa from 1966 to 1971 to study the genetics of several hunter-gatherer populations then known as Pygmies. He hypothesized that the dense forest environment where Pygmy populations lived influenced their genetics in various ways. The Pygmies were shown to have had adaptative traits, such as thermoregulation, reduced caloric intake, and improved mobility.

Research at Stanford University

In 1971, Cavalli-Sforza accepted a position as a professor of genetics at Stanford University in Stanford, California. He published papers derived from his studies in Pavia and formed collaborations with leading researchers in the field of genetics, such as Marcus W. Feldman. Feldman studied computational biology at Stanford University. He describes his partnership with Cavalli-Sforza in his 2017 research article “Cultural Evolution Theory: How Culture Evolves and Why it Matters.” Feldman asserts that he and Cavalli-Sforza shared an interest in the mechanisms behind cultural evolution, or the process by which human cultures develop over time. In their 1981 book, Cultural Transmission and Evolution: A Quantitative Approach, Cavalli-Sforza and Feldman classify and systematize various modes of transmitting culture. Those modes include parent-child, peer-peer, and teacher-student relationships. They incorporate data from sociological, archaeological, and epidemiological perspectives to develop a mathematical model. That model explains aspects of cultural evolution, such as linguistics, social values, and the spread of technological innovations.

Cavalli-Sforza met Albert Ammerman, who studied archaeology, in 1970. The two initiated a research collaboration that measured the spread of agriculture from the Middle East across Europe during the Neolithic period about 12,000 years ago. In 1971, they published their findings in a paper titled “Measuring the rate of spread of early farming in Europe.” There, they introduce the term “demic diffusion” to describe the migration of people. Ammerman and Cavalli-Sforza also emphasize the distinction from cultural diffusion, or the spread of cultural traits or technologies. In 1973, Ammerman and Cavalli-Sforza applied a demic mathematical theory called the wave of advance to model the spread of agriculture during the Neolithic period. That model contained parameters for reproduction rate, dispersal distance, and generation time. Ammerman and Cavalli-Sforza demonstrated that their model yielded a spread rate close to the observed rate, approximately one kilometer per year. They concluded that demic diffusion was more statistically significant in the spread of agriculture than cultural diffusion. That finding contradicted the opinions of most archaeologists at that time. Four decades after their proposal, a 2015 study from researchers at Harvard University in Cambridge, Massachusetts, used ancient DNA to conclude that demic diffusion was more significant in the spread of agriculture throughout Europe in the Neolithic period.

Cavalli-Sforza held his position as a professor of genetics at Stanford until 1992 when he was seventy years old. At Stanford, he engaged in research collaborations that examined the intersections among genetics, archaeology, and linguistics. In 1994, Cavalli-Sforza published The History and Geography of Human Genes. Cavalli-Sforza wrote the book with his co-authors Paolo Menozzi and Alberto Piazza, professors at the University of Parma and the University of Turin, respectively. The researchers connect demographic genetics, mathematical population genetics, archaeology, anthropology, and statistics to create an account of the genetic, cultural, and demic findings in human evolution.

Human Genome Diversity Project

In the early 1990s, the Human Genome Project began to gain momentum as an international research campaign to identify the full sequence of human DNA. Cavalli-Sforza and several colleagues at Stanford University and elsewhere proposed the Human Genome Diversity Project, or HGDP. The initiative aimed to collect and analyze variation between different populations. In a 1994 address at a special meeting of the United Nations Educational Scientific and Cultural Organization, or UNESCO, Cavalli-Sforza assured the scientific community that ethical principles would guide the work of the HGDP. Those principles included the ability for populations to opt out of participation and receive a portion of any financial benefits derived from their genetic material.

In a series of initial meetings, the participating researchers discussed sampling between 10,000 and 100,000 people and storing the genetic material in repositories. Instead of collecting only DNA, the researchers created lymphoblastoid cell lines, or LCLs. Scientists infect white blood cells with the Epstein-Barr virus to generate LCLs. The Epstein-Barr virus allows the cells to proliferate indefinitely in culture to ensure an endless supply of DNA. They stored the collection at the Center for the Study of Human Polymorphism, or CEPH, at the Foundation Jean Dausset, a French non-profit organization located in Paris, France, which promotes genetic and immunology research.

Starting in 2002, researchers deposited DNA from 1,064 LCLs. They paired the genetic material with information on the sex, population, and geographic origin of their sample. That repository contained fifty-one populations from five continents representing most of the world’s geographic regions. The HGDP elicited concern from various indigenous communities and human rights organizations. They argued that the HGDP facilitates racism, commercialism, exploitation, and cultural imperialism. Critics have also expressed issues with the informed consent process of the organizers of the HGDP. As of 2011, 148 research articles utilized the HGDP data, but its organizers and funders largely discontinued the project in favor of other genome initiatives.

Legacy and Impact

Cavalli-Sforza’s interdisciplinary work in genetics and anthropology bridged the gap between biological and social sciences in the study of human evolution. According to writer Alexandra Michel, many of Cavalli-Sforza’s collaborators consider him and Feldman co-founders of cultural evolution. Their book, Cultural Transmission and Evolution: A Quantitative Approach, established that the spread of non-genetic, socially transmitted traits among populations could influence human diversity similar to genetic transmission. Ammerman and Cavalli-Sfrorza’s demic diffusion concept became the dominant demographic change model for the Neolithic period during the 1980s and 1990s. While at Stanford, Cavalli-Sforza engaged in research that used many scientific disciplines to examine the biological and cultural facets of human evolution. He produced papers on constructing a human evolutionary tree based on blood groups and the classification of language families based on linguistic and genetic similarities within populations.

Cavalli-Sforza published about 600 research articles and contributed to around 20 books. His academic honors include his memberships in the American Academy of Arts and Sciences in 1973, the US National Academy of Sciences in 1978, and the UK Royal Society in 1992. He also received many other awards, such as the Golden Medal of the Italian Research Council in 1990, the Catalonia International Award in 1992, the Fyssen Internal Award in 1994, and the Balzan Prize in 1999.

After retiring from his teaching position at Stanford in 1992, Cavalli-Sforza and his wife began to spend half of each year in Italy. In 2008, they moved back permanently. His wife died in 2015, and Cavalli-Sforza died in August 2018 in Belluno, Italy, at the age of ninety-six.

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