Scientists studying vampire bats have isolated a gene that evolved to help the tiny blood-suckers turn hemoglobin into lunch. What would it take to plant such a gene into humans and give us the power to live off mammalian blood? New Scientist has the answer. [How Vampires Evolved via New Scientist]
So what did the bats eat before the gene "evolved"? How would eating the blood be a more successful solution? Wouldn't eating insects have better than "evolving" into something that ate something entirely different? Bat's usually eat insects, was there all of a sudden an insect shortage? Take a look at the wiki entry for vampire bats. There are all kinds of specialized digestive processes and unique physiological attributes that don't lend themselves to a transitional change model. That's the problem I see with many evolutionary theories. What the heck did this thing do in the "in-between" stages? I've never heard a good answer to that.