Captain patch is actually correct that there are variations of humans.
The vault dwellers are considered pure, and are not significantly different from the people before the war. The enclave believed these people were superior and their whole plan was to eradicate the rest.
The surface dwellers, the people who did not have the vaults were exposed to massive levels of toxin and radiation in the war, and in some areas FEV was released in an airborne state due to the explosions. The people suffered genetic damages, and mutated several key genes that allow them to survive much greater does of radiation, and heal it much faster than the people of the vault. They also mutate genes far more rapidly that people before the war, which confers a number of advantages and disadvantages, resistant to parasites and foreign diseases, higher rate of genetic disorders, and above all else they effectively evolve faster. They may not be noticeably different at this point, but every generation they get more and more genetically distinct from the "pure" humans, and the Enclave fear eventually they will outcompete, and replace them as the main human species.
Super mutants are genetically modified by FEV, and obviously different from normal humans.
Ghouls also, massive but not quite lethal radiation exposure.
Other smaller sub groups, the ghost people, marked men, others.