Nicholas A. Christakis ( ) (born May 7, 1962) is an American and Greek sociologist and physician known for his research on social networks and on the social, economic, biological, and evolutionary determinants of human welfare (including the behavior, health, and capabilities of individuals and groups). He is the Sterling Professor of Social and Natural Science at Yale University, where he directs the Human Nature Lab. He is also the codirector of the Yale Institute for Network Science.Tom Conroy, "New Institute Will Advance the Interdisciplinary Study of Networks", Yale News, April 11, 2013.
Christakis was elected a Fellow of the National Academy of Sciences in 2024. He was elected a Fellow of the National Academy of Medicine in 2006; of the American Association for the Advancement of Science in 2010; and of the American Academy of Arts and Sciences in 2017. In 2021, he received an honorary degree in economics from the University of Athens, Greece. He was awarded the Barry Prize for Distinguished Intellectual Achievement by the American Academy of Sciences and Letters in 2024.
In 2009, Christakis was named to the Time 100, Time magazine's list of the 100 most influential people in the world. In 2009 and again in 2010, he was named by Foreign Policy magazine to its list of top global thinkers.
Early life and education Christakis' parents are Greek. They had three biological children and adopted a Black girl and a Taiwanese boy. His father was a nuclear physicist turned business consultant and his mother a physical chemist turned psychologist.
Christakis was born in New Haven, Connecticut in 1962 when both his parents were Yale University graduate students. His family returned to Greece when he was three, and Greek became his first language. He returned to the United States with his family at age six and grew up in Washington, D.C. He graduated from St. Albans School.
Christakis obtained a B.S. in biology from Yale University in 1984, where he won the Russell Henry Chittenden Prize. He received an M.D. from Harvard Medical School and an M.P.H. from the Harvard School of Public Health in 1989, winning the Bowdoin Prize.
In 1991, Christakis completed a residency in Internal Medicine at the University of Pennsylvania Health System. He was certified by the American Board of Internal Medicine in 1993. He obtained a Ph.D. in sociology from the University of Pennsylvania in 1995. While at the University of Pennsylvania as a Robert Wood Johnson Clinical Scholar, he studied with Renee C. Fox, a distinguished American medical sociologist; other members of his dissertation committee were methodologist Paul Allison and physician Sankey Williams. His dissertation was published as Death Foretold, his first book.Gina Kolata, "A Conversation with: Nicholas Christakis; A Doctor with a Cause: 'What's My Prognosis?, The New York Times, November 28, 2000.
Career In 1995, Christakis started as an assistant professor with joint appointments in the Departments of Sociology and of Medicine at the University of Chicago. In 2001, he was awarded tenure in both Sociology and Medicine. He left the University of Chicago to take up a position at Harvard in 2001. Until July 2013, he was a professor of sociology in the Department of Sociology in the Harvard Faculty of Arts and Sciences; a professor of medical sociology in the Department of Health Care Policy and a professor of medicine in the Department of Medicine at Harvard Medical School; and an attending physician at the Harvard-affiliated Mount Auburn Hospital.
In 2013, Christakis moved to Yale University, where he is a professor of social and natural science in the Department of Sociology, with additional appointments in the Departments of Statistics and Data Science; Ecology and Evolutionary Biology; Biomedical Engineering; Medicine; and in the School of Management. He served as the Sol Goldman Family Professor of Social and Natural Science from 2013 to 2018, when he was appointed as a Sterling Professor, the highest honor bestowed on Yale faculty.
From 2009 to 2013, Christakis and his wife, Erika Christakis, were Co-Masters of Pforzheimer House, one of Harvard's twelve residential houses.Bita M. Asad and Ahmed Mabruk, "Christakises to Be Pfoho House Masters," The Harvard Crimson, February 17, 2009. From 2015 to 2016, he served in a similar capacity at Silliman College at Yale University.Emma Platoff and Victor Wang, "Christakis named Silliman master," Yale News, February 27, 2015.
Research Christakis uses quantitative methods (e.g., experiments, mathematical models, and statistical analyses). His work focuses on network science and biosocial science, and it has also involved sociology, economics, demography, evolutionary biology, evolutionary psychology, behavior genetics, and epidemiology. He is an author or editor of six books, more than 200 peer-reviewed academic articles, numerous editorials in national and international publications, and at least three patents. His laboratory is also active in the development and release of software to conduct large-scale social science experiments, pioneering its use beginning in 2009 (e.g., Breadboard, Trellis).
Christakis' early work was on physician decision-making and end-of-life care. He first began to study interpersonal social network effects in this setting in the late 1990s, with a series of studies of the widowhood effect, whereby the death of one person might increase the risk of death of their spouse. He developed a number of innovative ways to estimate the causal nature of these effects (e.g., by studying how the death of a man's ex-wife might affect his risk of death), and he expanded the scope of such work to analyze, for instance, how the precise diagnosis or duration of illness of the decedent might modify the risk of death of their survivor or how better quality of health care given to a dying person might reduce the risk of death of their survivor. In a 2006 paper in The New England Journal of Medicine that analyzed 518,240 elderly couples, he explored how hospitalization of a spouse, and not just their death, might affect a survivor's mortality risk.
Building on his early studies of network effects involving simple dyads of people (spousal pairs), Christakis began to examine the impact of illness and death through social networks of family, friends, and colleagues. Starting in 2004, he began to study "hyper-dyadic" network effects, whereby processes of social contagion moved beyond pairs of people. Using observational studies with his colleague James H. Fowler, he documented that a variety of phenomena like obesity, smoking, and happiness, rather than being solely individualistic, also arise via social contagion mechanisms over some distance within complex social networks (see: "three degrees of influence"). Later observational work explored how vaccination might spread across social networks. In a 2010 TED talk, Christakis summarized the broader implications of the role of networks in human activity.
In 2010, by exploiting the friendship paradox, a paper analyzed the spread of H1N1 influenza at Harvard University (as part of the 2009 swine flu pandemic) and showed that an understanding of social networks could be used to develop 'sensors' for forecasting epidemics (of germs and other phenomena). In another 2010 TED talk, Christakis describes this effort (and computational social science more generally). A follow-up paper in 2014 documented the utility of this "friendship paradox" "sensor networks" approach to forecast online trends using Twitter data.
Beginning in 2010, further work by Christakis and his collaborators used experimental methods and diverse data sets and settings to study social network contagion and structure, thereby enhancing the robustness of causal inference. For instance, a 2010 paper demonstrated that cooperative behavior could spread to three degrees of separation. A 2015 paper showed that vitamin use in developing-world villages could be made to be contagious. A 2022 paper used another experiment to show how a novel "pair targeting" algorithm could enhance population-level social contagion of the adoption of iron-fortified salt to reduce anemia in mothers and children in India. A randomized controlled field trial involving 24,702 people in 176 villages in Honduras published in 2024 documented social contagion in diverse health behaviors to two degrees of separation.
Christakis and colleagues also published a series of papers exploring how experimental manipulation of social network structure itself might enhance human welfare. Early work, starting in 2011, focused on how experimental manipulation of network structure could enhance human cooperation and economic productivity. Other work explored how network topology could affect human communication during a time of crisis or could optimize resource sharing. A 2019 paper in Proceedings of the National Academy of Sciences (PNAS) showed that experimentally re-wiring social networks could enhance human welfare without either redistributing or increasing resources. Additionally, an observational study of a novel monetary system (, a complementary currency introduced in Sardinia in response to the 2008 financial crisis) showed that k-cycle centrality was associated with economic success at the level of individual firms or the system as a whole.
In 2009, Christakis' group began to study the evolutionary biology, genetics, and physiology of social networks, publishing in PNAS a finding that social network position may be partially heritable, and specifically that an increase in twins' shared genetic material corresponds to differences in their social networks. In 2011, a follow-up paper on "Correlated Genotypes in Friendship Networks" in PNAS advanced the argument that humans may be metagenomic with respect to the people around them. Further work on this topic included "Friendship and Natural Selection" in PNAS in 2014, showing that people have a small but discernible preference for choosing as their friends other people who resemble them roughly as much as third or fourth cousins. In 2012, in a paper in Nature, Christakis' group analyzed the social networks of the Hadza hunter-gatherers, showing that human social network structure appears to have ancient origins. Anthropologist Joseph Henrich noted that "the crucial insight from this work is that understanding distinct aspects of cooperation among these hunter-gatherers must incorporate an analysis of the dynamic processes at the population level." Christakis and his colleagues did similar work mapping the networks of the Nyangatom people of Sudan in 2016. His group has also demonstrated that social networks are deeply related to human cooperation. These ideas are explored in Christakis' 2019 book, Blueprint: The Evolutionary Origins of a Good Society.
Work on the physiology of social networks, in particular with respect to the microbiome, started to appear in 2024, in Nature. Computational biologist Nicola Segata observed that understanding the spread of the microbiome through the social network is "changing completely the way we think", because such spread suggests that conditions with links to the microbiome (such as hypertension, depression, and obesity) could spread from person to person due to biological contagion.