Twins raised apart

Twins raised apart - what the research tells us

Written by the Australian Twin Registry and published in the AMBA Magazine
September 2015

Leading American twin researcher and author Dr Nancy L. Segal visited Australia as a guest of the Australian Twin Registry. She explains how she came to devote her life to studying twins, especially twins raised apart, and some of her latest findings.

“I am a fraternal twin and was always fascinated by the differences between my sister and me. I then wrote a college paper on twins and enjoyed the research so much it led to a life-long interest in this field”, Dr Nancy Segal explained.

Today Dr Segal is a Professor of Psychology at California State University, Fullerton, and Director of the Twin Studies Center that she founded in 1991. She has authored more than 200 scientific articles, but is probably best known for her latest awarding-winning book about twin lives, Born Together – Reared Apart: The Landmark Minnesota Twin Study, detailing her findings from a 20-year study of 137 separated twin pairs. 

According to Dr Segal, the highlight of her career has been working with twins raised apart and witnessing their reunions. Earlier this year, she helped to reunite the longest-separated twins on record – fraternal twins who had been apart for 78 years, living in the UK and US respectively.

“Twins who have been reared apart present a fascinating natural experiment, since they share genes but differ in environment, allowing researchers to identify how much of our behaviour and physical traits are guided by each factor”, she said. “But the complex, often intimate, sometimes uneasy associations between reunited twins fascinate me even more.”

Insights into child health 
Dr Segal shared her findings on twins raised apart and what they tell us about human behaviour as the keynote speaker at a recent Australian-first conference, Healthier kids: Insights from twin research. Hosted by the Australian Twin Registry and the Murdoch Children’s Research Institute in Melbourne, the conference brought researchers and twins together to highlight the vital contribution of twin research in the most formative time of life – from conception through birth and to adolescence.

“Genetics are even more pervasive in human development than previously thought.”

Dr Segal told the conference that her research into twins raised apart was revealing vital clues as to how we can raise our own kids to achieve happy and healthy lives. Her findings show that genetics are even more pervasive in human development than previously  thought, influencing nearly all aspects of our lives such as intelligence (70%), personality (50%), vocational interests (50%), sexual orientation (35% male, 18% female), and even job satisfaction (30%).

This evidence is leading to the rethinking of conventional ideas about parenting, child development and teaching. “Everyone can change and improve, but everyone cannot be the same. Sensitive parenting and teaching involves awareness and nurturance of each child’s special talents and preferences”, she explained. 

New research
Dr Segal’s passion for twin research shows no signs of abating, with upcoming diverse studies into twins who are parents, twinless twins, tacit coordination between twins, reared-apart and reared-together twins from China, unrelated lookalike pairs, and virtual twins (same-age unrelated siblings reared together from infancy who replicate twinship but without the genetic relatedness). She plans to broaden her ongoing research into twins raised apart by studying such pairs from different countries. If there are any Australian twins who would like to tell their story, Dr Segal would love to hear from you. Contact her at, or through the Australian Twin Registry ( Also, please visit her website ( to learn more about her work and participate in her research.

And what of the pair of 78-year-old twins whom Dr Segal reunited in the UK last year? Dr Segal recounted the scene of the twins shouting with glee upon seeing each other, “Sisters, how lovely!” “One of the twins told me that she had never had much interest in finding her biological family but was ‘speechlessly joyful’ to learn she had a twin sister”, Dr Segal said. Once the twins finished their testing with Dr Segal, they spent time with each other and their families. Tragically their time together was cut short by the sudden death of one of the twins only six months later. “Although it was immeasurably sad, the remaining twin told me it had been life-enriching to have met her twin even for such a brief period”, she said.