Are you saying that "Descent with modification...." is the mechanism by which new species are created? Has this been verified scientifically?
Yes.
Yes, I am confident this has been verified scientifically, by examining genomes of various species and by examining the fossil record (which isn't quite as free of good transitional forms as creationists allege). The mechanism is very slightly in doubt, that is, what causes new species to descend from earlier ones. Again, mainstream science says it's natural selection; a very small number of scientists challenge this.