Identical twins generally are not separated during adoptions, but Chinese officials had no record that Lily and Gillian were related at the time of their adoption in 2000.
As a result, the 6-year-olds are being raised by two different Canadian couples, but the parents have made concerted efforts to visit each other every few weeks so the sisters remain in contact. The unique experience is a fascinating glimpse into the age-old argument of whether nature or nurture has more of an impact on a child's development.
In February of 2000, the MacLeods and the Shaws traveled to China with an adoption group to pick up the newest members of their respective families. When they met their new baby girls, they couldn't help but notice how similar they appeared.
"On the record, they said no, the children were not twins," said Allyson MacLeod. "But off the record, they could not tell them apart and so they kept them in two separate rooms."
Neither family felt right about separating the sisters, but they were told if the adoptions didn't take place as planned, the babies would go back into the pool of potential adoptees and would still wind up separated.
"We had to look at the alternatives," Mike Shaw said. "Those alternatives were to have a larger extended family which would include us -- the Shaws -- and the MacLeods."
The Shaws and the MacLeods decided to raise the girls separately, but together. Gillian went to live with the Shaws, and their two children Eric and Heather. Lily went to live as a single child with the MacLeods. The families see each other every few weeks.
"This is a family situation and you do what you need to do for family," Kirk MacLeod said. "They are family."
The families have witnessed the girls develop in startlingly similar ways despite being in two different households.
"When Gillian took her first steps, I can remember calling Kirk and Allyson and they weren't home, so I left a message on the machine," Lynette Shaw said. "That evening they called back and Lily had also taken her first steps that day."
The girls got chicken pox within a day of each other, both are scared of clowns, and without knowing what the other was wearing, both dressed up as ballerinas for Halloween one year.
"The girls sound alike, the girls cry alike," Mike Shaw said. "They like music, they like to sing, they like clothes."
Being identical twins, their physical appearance is quite similar -- both are the same height and weight and sometimes they can't even tell each other apart in photos. But what fascinates researchers is their personality and developmental similarity despite the differences in their environment.
Lily has no siblings; Gillian has two. Lily's family is Presbyterian; Gillian's is Catholic. Lily's neighborhood is ethnically mixed; Gillian's is not. Lily's family celebrates some Chinese holidays and plans on sending her to Chinese educational classes; Gillian's family does not, instead wanting her to become part of Canadian culture.
"Same genes, different environment -- it's a real bingo into the argument of nature versus nurture," said Dr. Nancy Segal, author of "Indivisible by Two" and herself a fraternal twin.
"The fact that these girls are showing such matched patterns of development speaks strongly to genetic factors," she said.
New research shows that genetic differences between twins increase over time, especially in twins who have lived apart for a long time, but Segal is not sure if that will apply to Lily and Gillian.
"This is a unique situation because most twins either live together or are totally apart," Segal said. "Lily and Gillian see each other for more intense periods around the holidays, so it'll be very interesting to see how they develop … one would predict that they should be more alike than twins raised by separate families who never met."