We recently talked to Christian Kandler about his paper, "Unravelling the complex interplay between genetic and environmental contributions in the unfolding of inter-individual personality variability from early adolescence to young adulthood", which is scheduled for publication in an upcoming issue of the European Journal of Personality. Christian is professor of Personality Psychology and Psychological Assessment at the University of Bremen.
Read more about the article below!
Q: Hello Christian! Can you tell us more about yourself and what got you interested in personality psychology?
I am a rather introverted, agreeable and very conscientious – if not to say obsessive – guy. But sometimes, I can also be very extraverted and impulsive. But, you didn’t want to hear a self-assessed personality profile of myself, right? Love and work are the two drivers in my life. Without either of them I wouldn’t have a complete life, and with regards to this point I completely agree with Freud. I am married to a wonderful woman and a father of two lovely sons. They are my love, and investing in this love gives me energy, a power that is often underestimated by many of my colleagues. I can invest this energy in my work and as professor of personality psychology and psychological assessment -- I would say I have the best job, ever. I earn money by finding out about and learning new things that I can write down and teach others. The study of individual differences is a very broad and interesting field to me.
I am interested in finding out how and why we are so different. How can we map personality differences against the background of a broad personality concept such as relatively stable patterns of thinking, striving, feeling, and behaving? How can we capture interindividual differences in intraindividual personality development? And what are the sources of these observed differences? Here, I am particularly interested in the interplay between genetic and environmental sources. Studying twins over the life course helps to shed light on these sources of differential development.
Q: What is the current study about?
In the current study, we focused on the question, why do we become more different in personality between adolescence and emerging adulthood, and to what extent does the interplay between our genetic endowment and environmental circumstances drive the unfolding of personality differences during this period of life?
To us, there were at least three possibilities. First, the expansions of individuals’ deviations in their personality from others’ personalities may be due to an unfolding of individuals’ genetic endowments, just as individual differences in height take time to emerge in their adult-like magnitude of individual differences. However, a sheer genetic explanation of individual unfolding without contributions of the developmental context is less plausible. The unfolding of height differences, for example, depends on the availability of adequate nutrition. Thus, we proposed two further explanations of gene-environment interplay.
Increases in the genetic component of trait variance may result from an increasing number of very different chances and limits provided by the environment to express one’s own personality and thus its underlying genetic basis. This is what we call gene-environment interaction. When monozygotic twins are raised together, which is most often the case, accumulating interactions between their identical genes and their shared rearing environments would make them more similar than other siblings. This differential development would appear as an estimation of genetic unfolding, because genetically more similar individuals develop more similarly.
Or as a last explanation, which would also lead to a more similar developmental trend for monozygotic twins compared to other siblings, more freedom and autonomy during development may come along with increasing opportunities to actively shape and regulate their own personality development: People can be attracted to, create, or invest in niches and social roles that are consistent with their preexisting traits and would allow them to express themselves. They rather avoid contexts that are inconsistent with their predispositions and tend to change environments so that these fit better with their preexisting tendencies. This is what we call a gene-environment transaction.
In this study, we built on the data from two large population-based twin family studies, the German TWINLIFE study and the Norway Twin Study of Youth to find out which explanation fits the data best. If genetically identical twins developed more similar than fraternal twins over time due to an amplification of initial genetic differences, then this would be in line with the gene-environment transaction hypothesis. If novel genetic sources added to existing ones and initial genetic factors diminish over time, this would offer support for the gene-environment interaction hypothesis.
Q: What were the most important findings and implications of those findings?
First of all, we could replicate that personality variance increases during adolescence and that this increase comes along with an increase in genetic differences.
Furthermore, we found support for the second explanation: During development, we have different chances and multiple opportunities to express ourselves and to find fitting niches for our personality. Complex interactions between the genetic endowment and environmental circumstances can accumulate over time. These interaction effects can change with changing environmental opportunities and, thus, their effects on personality need not last on the long run.
Beyond this general trend for all investigated personality traits, we could also find interesting declines in differences in some traits in emerging adulthood. For example: we become more conscientious and less different in conscientiousness during the transition from adolescence to adulthood. This was exclusively environmentally driven, pointing to normative environmental pressure at least to show a minimum of being conscientious during this important life transition.
Q: What’s next? Can you tell us a little about where you see yourself in the near future?
My family and I moved to Bremen during the turn of the year, because I was offered a full professorship on Personality Psychology and Psychological Assessment at the University of Bremen. Together with other colleagues, I am working on the establishment of a new department of psychology there. So, currently, I have less time for research. But, I am also working on the development of a research group for studying the development and sources of individual differences. Therefore, in the long run, I hope we can establish an optimal basis for research and increasing knowledge on the patterns and sources of personality development across the entire lifespan.
Q: More generally, what are your hopes and expectations for the field of personality psychology in 2019 and beyond?
Based on a broad concept of what personality is, how it develops, and what the sources of intra- and interindividual personality variation are, personality psychology will enhance its interdisciplinary and integrative influence in the field of psychology and beyond. I will try to contribute my part to this development as good as I can.
Q: Looking back on your time as a graduate student, what advice would you give yourself?