By challenging Dr. Boyd to prove his assertion. The Catholic can point to lists of popes compiled by Church historians as early as the second century (e.g., Irenaeus
). Can he disprove their testimony? I would also point out to Dr. Boyd that the argument he uses is very similar to one that skeptics use to attempt to disprove the historicity of the New Testament. The same early Christians who compiled the New Testament and preserved the completed Bible that Protestants cherish also testify to the fact that the line of popes go back to St. Peter (see link above).