Dear Mr. Dad: My wife is expecting our first child. Initially, I was really excited, but lately I’ve been having these strange thoughts that the baby isn’t actually mine. I trust my wife completely and don’t want to mention this to her, but am I nuts?

A: In a word, No. At some point after the initial excitement passes, a surprising number of men find themselves experiencing exactly what you are: an irrational fear that the child their partner is carrying is not theirs. In his research with expectant dads, psychologist Jerrold Lee Shapiro found that 60 percent “acknowledged fleeting thoughts, fantasies, or nagging doubts that they might not really be the biological father of the child.” Like you, most of these men don’t actually believe their partners are having affairs. Instead, according to Shapiro, the feelings are symptoms of a common type of insecurity: the fear many men have that “they simply aren’t capable of doing anything as incredible as creating life, and that someone more potent must have done the job.” Fortunately, most guys get over these feelings pretty quickly.
Interestingly, irrational thoughts aren’t confined to biological dads. Men whose partners got pregnant using donor sperm—who actually didn’t do the biological creating—often have them too. A lot of guys worry that the sperm samples were switched and that they’ll end up with a child of a different race. Actually, it’s not so much race as physical similarity. Most couples who conceive artificially opt not to make the details of the pregnancy public. And, like any other dads, these guys hope their children will look like them—at least enough so that they won’t have to deal with the inevitable “Gee, the baby doesn’t look anything like you” comments.