SBS 200 Module 1 Theories and Methods in Human Development Example

Same Genes, Different Kitchens: The Nature and Nurture Debate in My Family and in Fifty Years of Twin Research

Student Name

Psychology and Addiction Studies Program, Aspen University

SBS 200: Human Development

Instructor Name

Month Day, Year

Same Genes, Different Kitchens: The Nature and Nurture Debate in My Family and in Fifty Years of Twin Research

My twin cousins, Maya and Lena, are identical. When they were three, their parents divorced; Maya stayed with her mother in a small town in Texas, and Lena moved with her father to Chicago. They saw each other a few weeks each summer. Now in their thirties, they share a laugh that makes the whole family turn around, a love of math and a tendency to worry about everything. But Maya teaches middle school, attends church every Sunday and votes one way; Lena is an accountant, is not religious and votes the other. At every family gathering someone asks which side won, genes or upbringing. This paper takes up that question, one of human development's oldest debates, using theory, research and my family's experience. My family here is a composite, combining details from several families for teaching; the research is real.

Ways of Explaining Development

Human development has been explained through several major perspectives. Psychoanalytic theories, such as Freud's and Erikson's, emphasize inner drives and the resolution of conflicts at different stages. Learning theories emphasize how experience and reinforcement shape behavior. Cognitive theories, especially Piaget's, describe how children actively build understanding through stages. Sociocultural theory, associated with Vygotsky, emphasizes learning through interaction with more skilled members of a culture. Ecological systems theory, developed by Bronfenbrenner (1979), places the developing person at the center of nested environments: the microsystem of family and school, the mesosystem of connections among them, the exosystem of settings such as a parent's workplace, the macrosystem of culture and values and the chronosystem of change over time. Each perspective takes a different position on how much development is driven from within and how much from the environment.

How Researchers Separate Genes and Environment

Because family members share both genes and environments, separating their effects requires special designs. Twin studies compare identical twins, who share nearly all their genes, with fraternal twins, who share about half. If identical twins are more similar on a trait than fraternal twins, genes are likely involved. Adoption studies compare adopted children with their biological and adoptive parents. Longitudinal studies follow the same people over time, showing how development unfolds and how early experiences relate to later outcomes.

Fifty Years of Twins

Polderman et al. (2015) conducted a meta-analysis of nearly all twin studies published over fifty years, covering more than seventeen thousand traits in over fourteen million twin pairs. They found that for nearly every trait measured, from physical characteristics to psychiatric conditions and personality, a portion of the variation was linked to genetic differences, with an average heritability across traits of about half. The rest was linked to environmental influences. For most traits, the pattern of twin similarities was consistent with many genes each having small effects. The study offers strong evidence that both nature and nurture contribute to almost everything researchers have measured.

When Environment Changes the Role of Genes

Heritability is not a fixed property of a trait. Turkheimer et al. (2003) studied seven-year-old twins, many from families living in poverty. Among affluent families, genetic differences accounted for a large share of the variation in IQ, while the shared family environment accounted for little. Among the poorest families, the pattern reversed: the shared environment accounted for much of the variation and genes very little. The researchers suggested that in poorer environments, children's genetic potential may go unrealized because of environmental constraints, so environment determines more of the differences among them. The study shows that nature and nurture do not simply add together; the effect of one depends on the other.

My Cousins Through the Research

The cousins' story fits both lines of evidence. Their shared laugh, mathematical ability and tendency to worry are traits that twin research finds substantially heritable, and they appeared despite very different homes. Their religion, politics and careers differ, and these traits are more shaped by family, community and culture. In Bronfenbrenner's terms, Maya's microsystem included her mother's church and a small-town school where she knew every teacher, while Lena's included her father's secular household, a large city school and a neighborhood where her friends' parents were professionals. The macrosystems differed too: the values of a small Texas town and of a large northern city.

My cousins also show the limits of personal experience as evidence. They are one pair, and they spent summers together, which means their environments were not completely separate. Their story illustrates the research; it cannot prove it.

Reflection

Before this module, I would have said that people are mostly shaped by how they are raised, because I grew up hearing that hard work and family values determine everything. The research has changed my view. My own tendency to anxiety, which I share with my mother and grandmother, now looks less like something I learned and more like a mix of inheritance and environment. That view is freeing, because it means I do not have to blame my mother for my worry or myself for not simply choosing to be calm.

Conclusion

The nature and nurture debate is not a contest with a winner. Polderman and colleagues show that genes contribute to nearly every human trait, Turkheimer and colleagues show that environments change how much genes matter and Bronfenbrenner's theory places development inside family, community and culture. My twin cousins, alike in temperament and different in beliefs, illustrate development as an interaction between what we inherit and where we grow up.

References

Bronfenbrenner, U. (1979). The ecology of human development: Experiments by nature and design. Harvard University Press.

Polderman, T. J. C., Benyamin, B., de Leeuw, C. A., Sullivan, P. F., van Bochoven, A., Visscher, P. M., & Posthuma, D. (2015). Meta-analysis of the heritability of human traits based on fifty years of twin studies. Nature Genetics, 47(7), 702-709. https://doi.org/10.1038/ng.3285

Turkheimer, E., Haley, A., Waldron, M., D'Onofrio, B., & Gottesman, I. I. (2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14(6), 623-628. https://doi.org/10.1046/j.0956-7976.2003.psci_1475.x