Some scholars have argued that John Mark's negative portrayal in Acts is a polemic against the presumptive author of the Gospel of Mark, Luke's primary source for his own Gospel. Adela Collins suggests, "Since the author of Acts also wrote the Gospel according to Luke, it could be that this critical portrait was intended to undercut the authority of the second Gospel." Michael Kok notes that "Mark's Gospel was a bit of an embarrassment to the refined literary and theological tastes of an educated Christian like Luke."