From Prehistoric Remains to Human Evolution
“My research straddles questions that lie at the intersection of the social and biological sciences, and has both applied and theoretical components,” Kuzawa said of his expansive research agenda. Broadly, this translates into studying how a person’s physical and social environment meshes with his or her basic biological functions such as eating, growing up, and having sex, and how this, in turn, affects a person’s development and health, as well as its impact on human variation and evolution.
The root of his interest in anthropology stems from an initial curiosity in archeology and studying the skeletal remains of the Hohokam of Pueblo Grande, a prehistoric Native American group who lived in what is now the U.S. Southwest.
“During my training in skeletal biology, I discovered that there is a great deal more that can be learned from studying living people,” he said, “and my interests quickly shifted to my current focus on human biology.” This has led Kuzawa to study the developmental origins of disease, brain energetics, male reproductive ecology, and human evolution, among other topics. These interests have also been fueled by his work on the Cebu Longitudinal Health and Nutrition Survey in the Philippines.
The Cebu Study and Biomarkers
In the 1990s, Kuzawa had become interested in testing British epidemiologist David Barker’s Fetal Origins Hypothesis, which postulates that cardiovascular disease (CVD) traces back to undernutrition in the womb. Kuzawa surmised that if this was correct, then such a pattern would show up as a high risk for CVD in adults who, decades ago, came into the world as malnourished, low birth-weight babies. He set out to study this pattern by implementing the first biomarker collection in the Cebu survey in 1998.
Such an undertaking proved challenging because Cebu City encompasses nearly three million people who inhabit a wide range of settings from rural to urban, he recalled. It took a full year to complete the first round of collecting blood and saliva samples in about one-third of the sample. By 2005, Kuzawa and his team were able to collect biomarkers in addition to DNA for the entire sample of 3,600 mothers and their children. To date, the Cebu Study has collected three decades of data on each of the study participants.
Tracing the Origins of DiseaseA well-publicized finding published in a 2012 issue of the Proceedings of the National Academy of Sciences (PNAS), with his former doctoral student Dan Eisenberg, concerned telomere length and aging. The research suggests that children of older fathers and grandfathers inherit longer telomeres—repeating DNA sequences at the tips of chromosomes—which could protect against aging and disease. The authors propose that this represents an intergenerational adaptation to changes in reproduction and survival. As men wait longer to become fathers for the first time (and are thus older), their children inherit the ability to live longer, and delay the age at which they become first-time parents as well.
Evolution, Fatherhood, and Brain EnergeticsKuzawa also aims to explain how hormones help coordinate human development and behavior. This has led to a substantial body of work on, among other topics, how testosterone influences male mating and fatherhood. A new father himself, he has co-authored 14 journal articles on the topic, with colleagues including Lee Gettler, a former doctoral student, and IPR’s Thomas McDade.
A study published in PNAS in 2010 investigated how rapid weight gain in newborn boys up to six months predict their height, muscle mass and sexual behavior as young adults, and a 2011 PNAS article examined the role of testosterone in male caregiving. In this study, Kuzawa and his co-authors show that a man’s testosterone levels drop precipitously following the birth of a child, likely to encourage caregiving. This was the first longitudinal study to confirm a causal relationship between fatherhood and the hormone. This responsiveness could help explain why human fathers care directly for their children, whereas no other member of the great ape family—the closest in genetic makeup to humans—does.
An additional area where Kuzawa is leading the effort to document how humans have evolved is in examining the human body’s pattern of energy use, and in particular, the costs of human brain development. “Humans managed to pull off an interesting trick,” Kuzawa noted. “Although we evolved a large and energetically costly brain, our body's resting energy expenditure is the same as predicted for a mammal of our size. How was this achieved?”
He is part of a collaborative effort supported by the National Science Foundation that is using positron emission tomography (PET) with magnetic resonance imaging (MRI) data to help answer this question by quantifying the energy costs of the human brain and how they change with age. In a forthcoming paper, his team reports that human brain energy peaks during childhood, which they argue helps explain why human growth is so slow in childhood: Human brain development is so costly that it requires slower growth to conserve energy.
With his wide-ranging interests in human biology and health, Kuzawa values the opportunity to interact with IPR researchers from other fields at Northwestern. “I firmly believe that a better understanding of our biology, including what makes us tick and how we evolved, is crucial for informed policy decisions aimed at improving human health and well-being.”
Christopher Kuzawa is professor of anthropology and an IPR fellow.
Kuzawa, C., L. Grossman, L. Lipovich, et al. In progress. Energetic costs and evolutionary implications of human brain development.
Kuzawa, C. 2013. You are what your mother ate? American Journal of Clinical Nutrition 97(6): 1157–58.
Eisenberg, D., M. Hayes, and C. Kuzawa. 2012. Delayed paternal age of reproduction in humans lengthens telomeres across two generations of descendants. Proceedings of the National Academy of Sciences 109(26): 10251–56.
Gettler, L., T. McDade, A. Feranil, and C. Kuzawa. 2011. Longitudinal evidence that fatherhood decreases testosterone in human males. Proceedings of the National Academy of Sciences 108(39): 16194-99.
Kuzawa, C., L. Adair, N. Lee, and T. McDade. 2010. Rapid weight gain after birth predicts life history and reproductive strategy in Filipino males. Proceedings of the National Academy of Sciences 107(39): 16800–05.