NORTHBORO — Bob, the new person hired in your department, is very friendly, a real go-getter and he says all the right things. He’s happy to meet everyone and you feel good about working with him.

But over time, you might notice that for no apparent reason Bob tells lies about little things: He says he had lunch at a fancy restaurant when he actually ate at McDonald’s. Or he may lie about something more important, such as the role he played in a project and report that several people worked on. Bob might take the report and walk into the CEO’s office and make it seem like he did most of the work, and that’s why he was chosen to come in to explain it.

Bob is a prime example of someone who James M. Silver, a former prosecutor and criminal defense lawyer, and Dr. Ronald Schouten, director of the Law & Psychiatry Service at Massachusetts General Hospital and an associate professor of psychiatry at Harvard Medical School, say exhibits characteristics of an “almost psychopath.” The two co-authored “Almost a Psychopath” (Hazelden Publishing, Center City, Minn.), which went on sale today.

“People who are an almost psychopath have an ability to lie that is startling,” Mr. Silver, 48, a Northboro resident, said during an interview last week. “These people are comfortable with lying because they’re not worried about getting caught. They’re not worried about how you feel about anything and they will use you or anybody else to get what they want. When cornered or caught, they will just continue to lie to the extent where people who know the truth might wonder about themselves. ‘Did we ask Bob to go in there?’ ”

Mr. Silver and Dr. Schouten wrote the book as part of a series of six that Harvard Medical School is doing. Information about the series can be found at www.thealmosteffect.com. The premise of the series is to look at psychological and psychiatric conditions of people who don’t quite meet the clinical definition of the condition. The first in the series was called “Almost Alcoholic.” The next book will be “Almost Addicted.”

Mr. Silver was asked as a criminal lawyer to co-author “Almost a Psychopath” because the book talks about behavior that can cross the line into criminal acts. He was referred for the job by his wife, Dr. Julie Silver, chief editor of books at Harvard Health Publications, the publishing arm of the medical school. Mr. Silver was a member of the defense team of the man known as Clark Rockefeller, who was convicted in 2009 of abducting his young daughter in Boston after his wife divorced him.

The best estimation of what causes a person to become a psychopath is a combination of genetics and environment, Mr. Silver said. Research shows that with a true psychopath, there is less mass in the area of the brain that processes emotions, and that impairs the ability to sense other people’s emotions. For instance, such people have difficulty sensing and understanding when a person’s face is showing fear or disgust.

Researchers also believe that being a person whose brain is predisposed to psychopathy and who is raised in a household where there is violence, instability and a lot of lying or manipulation may further that development. On the other hand, if the same child is raised in a family that practices empathy toward others, that child may never develop full psychopathy, said Mr. Silver, who teaches criminal justice and legal studies at Bristol Community College.

He said experts in the field, including to Dr. Robert B. Hare, estimate that one in 100 people is a true psychopath, and one in seven may be an almost psychopath. There are about 3 million psychopaths and as many as 45 million almost psychopaths in the country, he said.

Trained mental health professionals use the Hare Psychopathy Checklist of 20 characteristics to assess an individual. A zero means that characteristic is not present; 1 means it is somewhat; and 2 means it is present. The highest score is 40. Someone who scores 30 or