In the books it is made explicitly clear that Neville or Harry could be the chosen one as both were males born on the last couple of days of July in 1980, and both parents were a threat to Voldemort, and both parents were taken out by Voldemort/his supporters.
The only reason why it was Harry is that Voldemort thought he was the child the prophecy was talking about. By targeting him and trying to kill him, Voldemort marked him as his equal, while Neville got to live his life without that burden (though that doesn't mean he had an easy life).
While most fans agree that Harry is the unrefuted Chosen One, the final Deathly Hallows film (in particular) sways heavily toward highlighting a heroic Neville, revitalizing the debate regarding which boy is better suited for the iconic title. "The one with the power to vanquish the Dark Lord approaches ...
Choosing Neville to fulfill the prophecy would have made Voldemort successful in his goals. Snape would not have been driven by love to tell Dumbledore who Voldemort had chosen, or that Voldemort even knew of the prophecy, which means Dumbledore would not have known to put a Fidelius charm on the Longbottoms' house.
This theory states that Neville Longbottom, and not Harry Potter, was the chosen one that was mentioned in the prophecy regarding him and Voldemort. The following is said prophecy: "The one with the power to vanquish the Dark Lord approaches... born to those who have thrice defied him, born as the seventh month dies...
Voldemort learned that there were two boys that met the requirements of the prophecy: Aside from Harry Potter, the other was Neville Longbottom, who was born on 30 July, 1980, to a pair of Aurors who, like James and Lily Potter, had directly defied Voldemort on three separate occasions.
Dumbledore, to whom the prophecy was originally made, explains that it concerns "the Chosen One", a wizard that would have the power to vanquish Voldemort. This "Chosen One" would be born "as the seventh month dies", and thus the prophecy could refer to either Neville, born on 30 July 1980, or Harry, born on 31 July.
Absolutely. The only reason it wasn't Neville was because Voldermort had to personally mark the person in the prophecy as his equal and he decided to choose Harry. That's why Harry has the scar on his forehead.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Harry and Neville are both heirs of Gryffindor, as are all the other wizards who did the same throughout time.
Harry himself is a half-blood, since his pure-blood father, James, married a Muggle-born witch named Lily, and his maternal grandparents were Muggles.
The once shy and awkward Neville Longbottom showed his true bravery during the battle of Hogwarts and eventually became the head of Gryffindor House while also teaching new students Herbology, his favorite subject.
It took him five years, but eventually he figured out how to open the Chamber and release the Basilisk (CS17, HBP10). Harry was never the true Heir of Slytherin through his family line.
Neville is instrumental in the downfall of Lord Voldemort and eventually destroys the final Horcrux, which allows Harry to defeat The Dark Lord once and for all.
However, as Dumbledore explains to Harry, it could have meant another. Neville Longbottom, Harry's classmate, was also born at the end of July, and also born to parents who had thrice defied Lord Voldemort.
Neville became one of Harry's strongest allies, and there was a good chance that if Harry had truly died, Neville could have finished the job and destroyed Voldemort.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Lily's Protection In Voldemort's Blood Saved Harry
When Lord Voldemort returned Harry Potter and the Goblet of Fire, he used Harry's blood - which is partially how Harry survived Avada Kedavra in the forest.
' Neville comes from a long-line of pure-blood wizards, although we don't know as much about the individuals as we do with some other wizarding families. What we do know is that both of Neville's parents were pure-blood, as was his gran, Augusta.
The most likely reason why Lord Voldemort's nose disappeared and he devolved into such an evil-looking creature is that as he dabbled deeper into the Dark Arts, his appearance gradually became as distorted as what remained of his twisted soul.
Voldemort wasn't aware of Harry being a pseudo-horcrux because he didn't plan it, and Harry didn't know either until Voldemort “killed” him, but he actually killed the piece of soul kept in him.
If the prophecy is to be believed – specifically the definite article in the opening that states Harry is “the one with the power to vanquish the Dark Lord” – then it's only thanks to the prophecy's existence that Voldemort meets his downfall. No prophecy equals a victorious Voldemort and the darkest time line.
Why did Dumbledore not tell Harry how to destroy the Horcruxes? The reason that Dumbledore keeps his knowledge about the Horcruxes secret, (and presumably this is the same reason he did not tell the Order), is because he did not want the word to get around that he knew so many of the Dark Lord's secrets.
Neville's parents were both Aurors, and older than Harry's parents. To choose him first would be a little dangerous. After he tried to kill Harry, he lost his power, so he didn't have the chance to try to kill Neville. This has always been asked, but is just a common misconception.