New genetic material is not necessary. Changes to existing material will also do. A loss of genetic material could also work.
"New genetic material is not necessary."
Really? Then how do you get from Bacteria to Blue Whales? Through a loss of information?
Re: Sickle Cell
The symptoms of this "good" mutation include: acute attacks of abdominal and joint pain, ulcers on the legs, defective red blood cells, and severe anemia -- often leading to death.
Changes to existing material would in effect be new material unless the changes you're referring to are a loss of information... in which instance I ask again, how do you get from a self replicating asexual Bacteria, to a sexually reproducing Blue Whale via a loss of information?