Both genders spent equal time and effort looking at photos of the normal babies.

The study couldn’t explain the gender disparity. Elman noted that previous work has linked child abandonment and neglect to abnormal appearance, and even asked if the finding might challenge the concept of unconditional maternal love.

That’s too far-reaching a conclusion, cautioned Dr. Steven Grant of the National Institute on Drug Abuse, which funded the study.

The work is part of broader research into how we normally form attachments and what can make those attachments go awry, work that tests if what people say matches what they do. “Common sense would tell you one thing,” Grant said. “This doesn’t fit with common sense. It raises a question.”