Twin intellectual and personality differences are essential to a well-developed sense of self.

Identical twins and some fraternal twins look very much alike. Parents, close friends, and extended family expect that twins will develop at the same pace because of genetic similarities in appearance, personality, and behavior. My personal and professional experiences have shown me that in actuality, twins really do develop at different rates because of the interactions they have with caregivers and each other.

Twin A and twin B are a pair of fictional composites that I will use to illustrate my ideas of how and why twins develop differently. For example, twin A is more able to vocalize her feelings, and she cries and laughs more than her twin sister B. Being more comfortable verbalizing, she may start to take over communication with other people for the twin pair. Likewise, her twin sister B may be more physically active and she takes the lead in exploring their environment. Twin B finds the best places to play and have fun. Of course, these unique learning experiences will create different abilities in twins. Twin A talks all the time and her sister, twin B, looks for other children who like sports and competing in athletics.

Very early in life, differences are observable, lively, and attract attention from all types of caregivers and curious onlookers. Twins learn to rely on each other for the skill or ability that their co-twin is “stronger” at. This comfortable interdependence occurs naturally without direction from parents. Co-dependence, a natural........

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