One could say that the vampiresin these novels have evolved. Consider the classic vampire charactaristics. They feed on human blood, live in dark, drafty castles, hunting at night and sleeping during the day. They cannot go into the sunlight and they shapeshift into bats. Pretty typical right? This characterization could pretty much apply to every vampire story or movie you have ever read or seen.
However, the Vampires in Stephenie Meyer's novels have evolved into something totally different from the norm. Meyer has stepped away from garlic and holy water and created a vampire that some wouldn't mind running into. Perhaps this is what makes them so appealing?
The vampires in Meyer's novels aren't some blood-thirsty monsters. They are young, attractive, intriguing...people. The Cullens aren't unlike many of the families that live in Forks. They live as a family, feeding off the blood of animals, not humans. The sun doesn't kill them. They have made their home in a beautiful art-deco mini-mansion and they do not sleep in coffins packed with dirt. In fact, they don't sleep at all.
You could think of it as a form of cannibalism. Like early early humans may have eaten raw meat to survive but vampires do this to live and suck blood. There have been many different types of vampires but the most associated in novels would be the blood suckers. Evolution could be how they can gain new powers or how vampires pass on their vampire ness to other new borns.
I am going to go off a limb here and say that Vampires are the result of a human that had a mutation in their genotype. This mutation would consists of constant anosmia and a diet of rare meets. Back in the first human days much of the meat that was consumed was practically rare. The mutation reacts with the bite of a snake to form the disease of vampirism. This human with this disease then begins to effect others through a bite which automatically flare since it wouldn't know how to control the urge to feed. As times go on traits from each vampire bite begins to be pass on from vampire to new vampire like agility and strength (things needed to survive). This would also describe why some vampires have gifts and others do not.
Vampires and Sexual Selection:
Considering that vampires reproduce by biting their victims without killing them. Then any vampire that has a greater ability to bite their victims and control his urge to kill them would be able to produce more offspring. He would pass on his genetics and his offspring would then possess the same ability to control their urges and eventually outcompete other vampires. Over a period of time, this sexually advantagous trait would be amplified until eventually vampires would be able to easily control their need to feed on humans. This would contrast to Twilight portrayal of vampires as struggling to control their urge to bite bella.