News Archive 2009-2018

Professor of Psychology Sam Putnam: The Nature of the Nurture of Nature Archives

The College’s annual Convocation ceremony, marking the official opening of the 213th academic year, was held Wednesday, Sept. 3, in Pickard Theater of Memorial Hall. Following remarks by President Barry Mills and Dean of Student Affairs Tim Foster, Professor of Psychology Samuel Putnam delivered the convocation address, traditionally given by a faculty member.

Convocation Address

Thank you, President Mills, for this introduction and for this opportunity. Convocation really is one of my favorite moments of the College and it is an honor to welcome the class of 2018.

My scholarship focuses on the nature — and the nurture – of human development. My initial interest in this topic did not arise in a psychology course. Rather, it was sparked in a movie theater in Visalia, California, in the summer of 1983. The comedy “Trading Places,” filled with slapstick moments, including those involving a deranged Santa Claus and a sex-starved gorilla, was an unlikely source of intellectual curiosity. The premise of the movie involves a bet between brothers – two wealthy commodities brokers who want to see what happens when a homeless beggar, played by Eddie Murphy, is caused to trade places with a privileged trader, played by Dan Aykroyd. One of the brothers is convinced that the successes and failures of these individuals were due to the environments they had encountered – the schools, parents, and neighborhoods that had made them who they were. The other brother believed that the individuals were born as they were, and that they alone were to credit or blame for their station in life. This movie was made purely for entertainment purposes, but as I sat in the dark theater, I was entranced by the question that had been posed. Do we become who we become because of our nurture, or are we who we are because of our nature?

So, why am I telling you this little story of how my curiosity was sparked? I’m telling you because I want to suggest to you that the beauty of a liberal arts education is the opportunity it affords for cross-pollination. It is possible that you could develop a truly unique perspective on American Government from the literature you are exposed to in your first-year seminar on God and Monsters. Principles you learn in coursework for Differential Calculus could lead to a new way of understanding the development of Culture and Power in the Andes. Gaining perspective on the Philosophy of Altruism might lead to a new technique to understand the fighting behavior of crickets in a neuroscience laboratory. Both what you learn and how you learn to think in one discipline can provide inspiration and understanding of any other field.

Of course, though, your Bowdoin education will also compel you to learn deeply. Each of you will be a relative expert in something by the time you gather on the steps of the Art Library for commencement 4 years from now. As I progressed through college, the spark provided by a cheesy comedy grew to a consuming preoccupation, and I spent much of my time attempting to determine whether the behavior of my friends, my family, my roommates, my teachers, and my self was caused by nature or nurture.

Many of you in the audience intuitively grasp the folly of searching for an answer to the question of nature OR nurture. It may be obvious to you that BOTH nature AND nurture play a role in shaping behavior. At the time I was an undergraduate, however, it was my perspective that the power of our genes was getting the short shrift. Many of the parents I knew were too eager to take undue pride in their kids’ accomplishments, or to blame themselves for their children’s struggles. The reason for emphasizing nurture is obvious: We feel as if we can “see” the environmental factors that seem to shape the person. We believe that one child is aggressive “because” her parents hit her when she misbehaves; another child is smart “because” his parents read to him every night. The fact that these components of nurture are observable makes them more real to the untrained eye.

What is apparent, however, may not necessarily be real. Consider the aggressive child who is spanked. Maybe spanking leads to aggression, or maybe the child who hits others has simply inherited a genetic profile similar to their parent who hits them. Perhaps the smart child and reading parent are similar in behavior solely because they are similar in biology. The fact that, in most cases, parents provide both nature and nurture creates a serious challenge to disentangling these influences. This challenge is so substantial that it was once suggested to me that “The effect of nature on personal development is amenable to science, but the effect of nurture is less so.” Of course, this is nonsense. Any phenomenon, natural or social, can be studied through a scientific lens. A critical tool in my field is time. By systematically observing differences in the ways that people in one circumstance change over time in comparison to the ways that people in a different circumstance change over time, we can generate powerful inference regarding causality.

Given the apparent and proven power of the environment, then, the next important question to answer is “Do genes matter at all?” The initial studies addressing this question made use of experiments of nature and circumstance. By comparing the similarity of identical or nonidentical twins, or adoptive and biological siblings, several studies converged in suggesting that a large proportion of our individual differences – in our intelligence, in our personality, in our self-control, and even in our attitudes toward religion and social issues – has roots in our genes.

More recently, the focus has shifted from showing that genes in general were linked to human behavior to the study of which genes. When the human genome was decoded over a decade ago, the expectation was that we would soon know what genes “caused” a host of disorders. A number of studies were published indicating individuals possessing a given allele were more likely to be schizophrenic, depressed, or aggressive than those with a different allele. But then something curious happened: other studies, conducted with different samples, failed to confirm the originals! How could this be? How could one gene “cause” a disorder in one group of people but not “cause” this disorder in another group?

The basic truth is that these studies of nature had failed to take nurture into account: they had largely disregarded the fact that the activity of genes is governed by influences within and beyond the cell. Although the DNA sequences that make each of us unique was determined at the moment that sperm entered egg, whether and when a given gene is expressed depends on its surroundings. Yes, a certain gene may be linked to a certain outcome…but only if it is complemented by a certain environment.

The current search for factors that moderate the effect of individual genes is one way in which our field has advanced from the relatively unsatisfying question of “nature or nurture” to the far more exciting question of HOW: how does nature combine with nurture to shape development?

An intriguing answer to that question is that nature affects development by affecting nurture. For example, consider research on temperament, attachment, and psychopathology. A number of studies have suggested that some children have a genetic predisposition to be “difficult.” From early infancy onward, they are negative and unsoothable; later, they are prone to poor relationships and conduct that is harmful to themselves and others. Their biological disposition, though, is not destiny. Rather, their nature primarily leads to problems by shaping the nurturing they receive. Put simply – and tragically – these babies act in a way that makes it hard for parents to treat them well.

Although this is what often happens, it isn’t what must happen. In a classic set of studies, 1-month-old infants who were identified as difficult were randomly assigned into two groups: one whose parents were given information about temperament, as well as specific techniques to soothe difficult infants; and a separate control group who received no such training. Whereas – as expected – the control group was highly likely to develop an insecure relationship with their mothers, the intervention group was not. Despite their early tendencies, they developed healthy attachments.

These findings of nurture changing the child’s nature were important, but the subsequent findings were even more meaningful. As these children grew, the intervention children were actually treated differently by others. Other kids were more likely to seek them out, enjoy their company, and play happily with them. In other words, the nature of their actions changed their nurture. Even later, intervention children were less likely to become aggressive or depressed, apparently because they were more likely to develop healthy relationships with their peers. This example elegantly shows how nature affects nurture, which affects nature, which affects nurture, in a never-ending dance of give-and-take.

At this point, I’m hopeful that you all buy into the notion that your biological nature both shapes, and is shaped by, the environments you encounter. Recent research, though, suggests a more fantastic possibility. The environments that you encounter not only change your biology – they may change the biology of your children and your children’s children.

In your earliest biology lessons, you were presumably taught that acquired traits cannot be inherited. In the classic example, a parent who loses a leg does not give birth to a one-legged child. To me, the notion that each generation got a clean slate was a fundamental fact…until a few years ago.

Biologists, geneticists, and psychologists are now showing that the environments experienced by parents can change aspects of the genome that, along with DNA, are passed on to their offspring. For someone who has spent decades working under the paradigm that genes –and ONLY genes – are passed to offspring from parents, and that environments interact with genes only AFTER conception, the new findings on intergenerational epigenetics are mind-blowing.

The groundbreaking study in this area showed that individuals who lived through famine at certain points in development had grandchildren who were more likely to have diabetes than those who had not lived through famine. Extending these findings to behavior, it has been shown that rats raised in “enriched” environments with multiple opportunities to learn are not only better than other rats at running mazes themselves. They have offspring – and offspring of offspring – and offspring of offspring of offspring – who are good at mazes, even when those great grandmice are not raised in enriched environments.

The implications of these findings are incredible. What happens to you, through choice or by accident, during your life can not only change the way your body and mind work. It can change the way your great grandchildren’s bodies and minds work.

A final note about development concerns crucial periods. Moments of transition – times when things change – are particularly important for shaping developmental trajectories. Class of 2018, at this moment, you stand on the threshold of an exceptionally important transitional time of your life, not only in terms of intellectual opportunities, but social ones. The influences you encounter – the people you choose to spend time with – in the next four years could have an immense effect on the direction you take.

The logical extension of that fact is that the environments you cause – the nurturance you provide to the people sitting next to you right now – could shape not only your peers’ experiences during college, but the biology of future generations.

In relation to this serious responsibility, I’d like to close this talk with a quote from another movie produced in the 1980s. In the words of Bill and Ted, spoken in the course of their adventure…

“Be excellent to each other.”

(“And party on, dudes!”)