How does the last name of "Finch" contradict the whole novel?
Finch is Scout's last name and is as well a name for a type of bird, so I think it somehow contradicts the mockingbirds--Boo Radley and Tom Robinson.
But does anyone know exactly how it is contradicting the novel?(Please be specific)
I think you're reading too much into the bird imagery. The title To Kill a Mockingbird refers to the superstition that bad luck will come to anyone who kills a mockingbird. (In some states, it is illegal to kill any songbird.) One of the themes of the novel is that people are subject to their unlucky life situations.
It might interest you to know that Lee's mother's maiden name was Finch and that Lee's father was an attorney. See the biography linked below. It is more likely that she is just honoring her mother by giving the main characters her name than that she is trying to say something with bird imagery. Think of Scout as Harper Lee as a child, telling a story about growing up in the pre-civil rights south.
I’m not sure if “finch” as the last name of Scout and Atticus “contradicts” the novel, but it might complicate the attempt to contrast it with the mockingbird. Interestingly, the finch is the species Darwin particularly studied in the Galapolos, which resulted in his theory about evolution. He noticed how the finch had many different subspecies, that there must have been an original “finch” that had evolved into many different birds that were still finches. Darwin wrote, “Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends." In the world of birds, “finch” refers to many different kinds of birds; it is not unlike the frequency of the name “Smith” in regard to people—many different kinds of people bear this name. Some finches might be territorial, but most are not, just going about their business being birds, not bothering anyone. If “finch” signifies complexity and diversity in development in the bird world, then its use in the novel, might suggest complexity in development in the human world. Perhaps Lee used it because it is a rather generic term of a typical bird; perhaps she meant it to signify a commonality with mockingbirds, which also don’t bother others, although they, unlike the finch, make a distinctive song.