Deng Yajun at work in her lab Photo: Courtesy of Deng Yajun

As a scientist who analyzes the building blocks of life through a string of DNA codes, Deng Yajun, 40, never expected her career to take such a mysterious turn nine years ago. This trajectory has brought her into contact with a myriad of life stories, including many concerning the most private and complex corners of human nature.

In May 2002, China opened judicial forensics services including DNA paternity tests. These used to be solely run by public security and judicial authorities. When they were passed to independent institutes, Deng, with her eight years of experience as a professional medical examiner with a local public security bureau in Xi'an, Shaanxi Province, became one of the first DNA paternity test experts in the Center of Forensic Sciences of Beijing Genomics Institute. In October of 2003, she welcomed her first client.

20% of negative results

Over the past nine years, Deng and her center have received more than 20,000 paternity test requests from around the country. No matter how old the child is, all of her clients want to assess one thing: the truth about the child's biological parents.

"Everyday, I need to face all kinds of people with their own purposes. Most of them want to know whether they are truly their children's parent, while some want to know the consequences of a long-past extramarital affair. There are also women who want to prove their innocence or find their children's true father," Deng said.

Though the number of cases handled by Deng's center has grown almost tenfold over the years, from more than 600 to close to 6,000 in 2011, negative results have stayed steady at just over 20 percent.

"It means there are more than 4,000 children tagged as 'born out of wedlock' by our test results," said Deng.

A moral outcry originally questioned an exceptionally high elimination rate of 28 percent announced in 2006. Deng rebuffed these claims, saying the figures are not surprising since they only reflected a pool of around 1,800 cases handled that year and do not indicate a broader average.

However, she admitted that in most cases, the result of the test comes as a judgment, and is the last defense holding a marriage together. Because of this, the test itself is often criticized as being to blame for a broken marriage.

After seeing so many people's lives being changed by the results she presented, Deng felt helpless.

"The paternal test is just a technology, there is no reason to ask a technology to take moral responsibility, just as we cannot condemn a gun for killing people," said Deng.

Listener of secret stories

As a scientist, Deng sees herself as a cool-headed and rational person. However, she was surprised to realize that after meeting with many of her clients, she had unintentionally become privy to their deepest secrets.

Most of the time, Deng is a listener for her patients. "On the other end of the phone, she poured everything out before you could figure out what the whole picture was," Deng said, describing her encounter with a client who begged Deng to falsify results as her husband had taken their son for a test without telling her.

 But sometimes, she finds herself being the only person her patients can turn to. She recalls her first. It was a pregnant woman in her 30s who was trying to figure out her baby's real father, her lover or her husband. But as the fetus was only 2 months old, Deng was unable to give her a definite answer.

"She asked me what to do, with a very complex feeling," Deng remembered. Three days later, the woman called Deng and told her she had to give up the baby. "I couldn't afford to see my marriage die because of a remote possibility that the baby was not my husband's," she explained.

In Deng's office, a reception room is where the blood samples needed for the test are collected and then passed to the lab through a small window. In Deng's eyes, this reception room is like a stage, "every single story happening here could become a play, happy or sad, beautiful or ugly. They are simply true stories, but you could hardly imagine it if you didn't see it for yourself," said Deng.

Biggest victims of the test

As the mother of two 5-year-old twin boys, Deng said she could never forget the eyes of children when they learned their parents were not who they thought.

Deng recalled a client's complete change of attitude toward his son. "Before the test, the boy was a little emperor, but seven days later, when the father realized the child was not his, he simply pushed the boy away from him."

"As a professional paternity test expert, I respect results based on science. However, as a woman and mother, I really can't meet the innocent eyes of those children. In such moments, I always want to hold the children, telling them it's not their fault," she said.

Two sides of a coin

Of course, the job is not all bad. One of Deng's favorite stories came after a positive result. It brought a father out of depression, and five years later, Deng read a story about his son winning an international competition in a local newspaper.

"Any technology has two sides, it can bring harm to some, but benefit others," said Deng.

Deng admits that the longer she is in the trade, the less interest she has in listening to patients' stories. However, she still finds herself crying after hearing a touching tale, or angry at people acting irresponsibly toward their families.

Old stories also keep coming back to her. "I am wondering whether my first patient had a chance to have another child with her husband," said Deng.

Finally, all of the faces, moments and stories that deeply impressed her have recently been turned into a book, Secret Files of Paternity Tests, compiled by one of Deng's friends based on the stories she told.

"The DNA test makes it possible to uncover problems that have been there all the time, and I just hope that from those sad stories, people can learn lessons to keep their families happy and stable," said Deng.