It Takes Training and Genes to Make a Mean Dog Mean. [The icing on the cake of this article is in bold below]:

About four million to five million people are bitten
each year by the nation’s 55 million to 59 million dogs,
according to statistics compiled by the Humane Society of
the United States and the Centers for Disease Control and
Prevention, which consider dog bites epidemic.

The reason for the bites vary. Some are clearly accidental,
or the dog is provoked, while others result from various
forms of abnormal aggression in the dog.

Perhaps more significant, a statistical analysis by researchers
at the Humane Society, the C.D.C. and the American Medical
Veterinary Association and published in the Sept. 15 issue of
The Journal of the American Veterinary Medical Association
shows that between 1977 and 1998, pit bulls and Rottweilers
accounted for more than half of the 238 fatal attacks on
humans.

That same study shows that since 1975 dogs representing
more than 30 breeds have engaged in such attacks. Because
so many types of dog can be involved in fatal attacks,
including, in the past year, a Pomeranian and Lhasa apso,
experts in dog behavior have consistently argued that
outlawing specific breeds fails to address the greater
problem of all dogs that pose a threat to people and other
animals.

New York Times