Correct me if I'm wrong, but I thought the Spartans from the Spartan II program received biological augmentations to their bones, tissues etc to make them super strong, super fast and super agile. Isn't it mentioned in the books? I don't recall reading anything about genetic modifications being done to the Spartans. If you've read Ghosts of Onyx, then you'll be familiar with the Spartan IIIs, and even they didn't receive genetic modifications. They were augmentations, including one that helped them perform better under highly stressful conditions. Even though it was probably beneficial to cover the subject of genetic modifications, it doesn't really apply to the Halo Universe. Then again, please correct me if I'm mistaken...

Its good to finally see someone take this issue seriously.