As sisters only four months apart, Julie and Sara Curry grew up being peppered with questions from confused classmates. Your mom was in labor for four months? asked one friend, said Sara, 19. How is it possible? others inquired.
The Curry sisters, college sophomores who live with their parents in this high desert town on the outskirts of San Diego, are what Nancy L. Segal, a psychologist who is researching behavioral differences among twins, refers to as virtual twins. By her definition, virtual twins are unrelated children born within nine months of each other who enter a family, through birth or adoption, in the first year of life. Since 1991, Segal has been studying 137 such sets of siblings, whose average age difference is three months.
As scientific subjects, virtual twins provide a rich pool of material for researchers tackling the nature-versus-nurture question. In Segal’s studies, as in so many involving biological twins, it seems that nature is winning.
Raised together essentially from birth, or at least since infancy, virtual twins may be genetic strangers, but they share an environment from an early point in life.
A twin herself, Segal runs the Twin Studies Center at California State University, Fullerton, and is the author of two books on twins. She said her work has shown that virtual twins have less in common in terms of behavior, intelligence and decision-making than fraternal or identical twins, including those reared apart, or even biological siblings several years apart in age. Her research has appeared in publications like the Journal of Educational Psychology over the last few years.
“I expected the virtual twins to be more alike than they were because they had been raised together all their lives,” said Segal, who has also studied hundreds of pairs of fraternal and identical twins, including dozens reared apart. “Yet they were so much less alike. It gives us another piece of evidence in the whole nature-versus-nurture puzzle.”
While it is difficult to quantify the phenomenon, researchers say that virtual twins are an increasingly common result of Americans having children later in life, facing fertility issues and forming families through a patchwork of channels: adoptions, surrogate births, natural pregnancies and fertility treatments, which can lead to multiple births. Many parents, having struggled with infertility for years, pursue several avenues at once to increase their chances of having at least one child. If two adoptions or an adoption and a pregnancy work out at about the same time, the stage is set for virtual twins.
Peggi Ignagni of Oberlin, Ohio, had been trying to become pregnant for nine years when she and her husband, Tony, applied for a foster-care license, hoping they could adopt an infant after taking him into foster care. They got Nickholas when he was 3 days old but decided to proceed with in vitro fertilization, fearing that they might not be able to keep the boy. The fertility treatment worked, and Ignagni became pregnant with triplets who were born eight months after Nickholas. She and her husband, who owns a medical device company, now have four 6-year-olds. “At least they were all potty-trained within the same week,” she said.
In the case of the Curry sisters, Sara was adopted at birth by Deborah and Dave Curry, who are both retired from the Navy. The couple had tried having children for almost four years before they arranged for a private adoption. Deborah Curry became pregnant with Julie a month after Sara’s birth mother chose them as parents. When they left the hospital with Sara, they were stopped by a security guard and asked to explain why they were leaving with a newborn when Deborah Curry was obviously still pregnant.