The first issue with this theory is how strongly Harry resembles James. The only difference in their physical appearance is their eye colours and Harry's scar. They have the same messy black hair, the same shape face, the same height and build. Several characters, throughout the series, have remarked on this similarity and compared the two. Harry even mistook his time travelling future self for James in Prisoner Of Azkaban. He has also inherited James' skill at broomstick flying and Quidditch, and his Patronus form mirrors James' Animagus form of a stag. It is highly improbable that Harry would resemble James in this way if James wasn't actually his biological father. Some mashabiki claim that the resemblance is actually proof that Lily magically altered her son's appearance to hide her infidelity and save her marriage, but in that scenario it is unlikely that her magic's effect would prevail for several decades after her death, even affecting the appearance of her grandsons too.
The sekunde issue is the way Harry maoni James throughout the series. He sees James as a role model, feeling proud when he is compared to his father. Harry thinks of James and how he died fighting when he duels Voldemort himself in Goblet Of Fire. This is the reason he felt so disappointed, disillusioned and hurt after seeing Snape's memory of being bullied kwa James. mashabiki of this theory point out that Harry gave his son Albus the middle name Severus, but ignore the fact that he first gave his eldest son the name James. It would make no sense for Harry to admire and look up to James in this way throughout the series, if the man wasn't actually his father. It'd make no sense for such a revelation not to actually be made to Harry, au even clearly confirmed within the story. This would far too dramatic a twist to be left to inference and rumour alone.
