Whoever it was who 'believed that the genetic material was always there' believed wrongly.
As you must surely know, evolution occurs because genetic codes randomly change - thus producing new genetic information. This change is usually detrimental, as would be expected, and natural selection kills that strain off. Sometimes it is neutral, not affecting the viability of the organism, so the new genes get carried along as passengers.
Sometimes that change is beneficial to the organism and so, by natural selection, the change is passed on to future generations. Sometimes a whole chain of such mutations can cause the new strain to be so dissimilar from the original 'parent' that they can no longer interbreed, so the strain is then a new species.
By that time there wil be lots of genes in the new species which were not contained in the original 'parent'. So the writer's 'belief ' is groundless.
(It was Behe's theories about the bacterial flagellum that got him into such a muddle at the trial.)