Looking at the relative importance of nature vs. nurture is a highly regarded approach to research aimed at understanding intellectual and social emotional personality development in both identical and fraternal twins. These twin findings transfer to single-born individuals as well. In other words, “How relatively important are these variables of inheritance (genetics/nature) vs. environment (nurture) to physical and psychological development?”

Researchers suggest that the development of identity is a primary factor in decision-making ability. They agree that identity determines who an individual becomes psychologically as they actualize or grow into maturity (Winnicott, 1960). An equally important question is: What contributes to an individual personality in each twin of a twin pair? In other words, besides nature and nurture, what else contributes to the development of individuality in twins? For example, why is one twin more outgoing and the other more emotionally sensitive? Why is one twin seemingly more dominant, sure of themselves, and able to make decisions? Why is the other twin reluctant to express themself?

Undeniably, social interactions and attentiveness from parents, close others, and teachers contribute to the development of dominance and non-dominance in twins. The twin dynamic, based on parent perceptions of the children, is a critical factor: “Is my son more like his mom or dad or one of his grandparents?" "Is my daughter more like her mother or father?” The comparing and contrasting of twins begins early in life and typically never stops as people ask pointed questions about how each of the twins are different.

How Do Differences Develop in Twins?

Parental attachment and the parents’ perception of each child are the basis of the development of differences in twins (Winnicott, 1970). Alongside parental attachment and perception by significant others, some of the side effects of being a twin are created by twin comparisons by family and outsiders who are intrigued by twins.

For example, a mother might say, “Kimberly is just like her father and Carl is just like his mother.” These associations often seem to stick to the twins and live on within the family as these associations grow in their world. The determination of “which twin is like which parent” will play a part in determining individuality.

This twin dynamic creates differences between twins. For example, one twin in the pair is more demanding and the other twin is more compliant. These differences grow stronger as parents adjust to each child’s unique way of reacting to other people and to their twin. Seeing twins as different and giving them what they need, not what parents think they need, is essential. Attention to a parent’s effectiveness and attentiveness to the unique qualities of each child is crucial and creates individuality between twins.

While dominance between twins varies depending on what event is taking place, the more outgoing twin will be more comfortable showing off. The shyer twin might take the dominant role in making plans for the pair. In my opinion, there is no one “dominant” twin, because this personality characteristic is shared within their twin bond, and frequently changes. For example, one twin may take the lead in decision-making expression but will be aware of what their twin will support/allow.

The use of the word “dominant” is an old-fashioned way of trying to understand how twins become themselves and not copies of one another. While trying to understand why differences develop is fascinating and important and helps parents, teachers, brothers, sisters, and grandparents engage with twin children more effectively, it is a complicated process. Understanding how twins learn to be different and learn to accept each other is a process that needs to develop carefully because it has a profound impact on achievement and happiness for each twin and the pair. Accepting differences can limit fighting and, later, estrangement.

Identical twins share the same genetic endowment and react to the same environment. Fraternal twins are not similar genetically but share the same environment growing up. The comparison between these two types of twins indicates the impact of nature vs. nurture upon twins and opens up the question of how important natural genetic inheritance is. For example, a very smart set of successful parents will likely give their children a strong genetic endowment, which can lead to academic success and good managerial skills. Parents with learning disabilities might transfer them to their children, which may limit their success if not attended to by specialists.

Dominance is one of the key factors that leads to a unique sense of self and identity in twins. Other factors such as interest in communication (talking and writing), physical activities, and creativity help define real differences between twins. Parents should react to unique parts of each twin’s way of solving problems. Find similarities and differences and acknowledge them to prevent imposing a standard of “you have to be copies of one another”—labeling that is sure to be harmful. Here are some suggestions:

Treat your children as different based on actual real differences, not because they remind you of your own parents or siblings.

Let each child be in charge of their own clothes, toys, and friends—as much as reasonably possible and age-appropriate.

Spend time alone with each child.

Do not make one child responsible for their brother or sister’s behavior or responsibilities.

Avoid comparing your twins, as this type of evaluation diminishes their individuality and intensifies fighting and competition.

Your children will have different problems, as twins are not copies of each other. Help each twin with the issues they are facing. Do not impose the problems of their sister or brother on them.

It is difficult and time-consuming to raise twins. Work endlessly to treat them as individuals, remembering that promoting dependence creates long-range problems that are hard to get over. Find help from others who are twins or who have familiarity working with twins. Talking and teaching about the importance of separate experiences will help ensure that each person follows their own path.

www.estrangedtwins.com

Winnicott, D.. 1970, in E. Anthony and T. Benedek (Eds.), Parenthood: Its psychology and psychopathology.

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