People think this obsession with size has only been the last 20 years or so, but that's not true. Huddersfield Ben was responsible for producing most of the foundation stock of the Yorkshire Terrier. He was an extremely popular stud dog, who weight between 9 -12 lb, but he regularly sired stock that competed in the under 7 lb limit.
Huddersfield Ben - Wikipedia, the free encyclopedia So due to Hudderfields Ben, Yorkies could compete in the toy group. Now Ben died in 1871, so Yorkies have been in the toy group, since the beginning of the breed. I think around 1919 a 3 pound Yorkie won best in breed, and over time good breeders learned it's not safe to breed females under 5 pounds to hard on them.