Miniature Labradors do not exist in nature, because they are domesticated dogs created by artificial selection. Breeders create Mini Labradors in particular by crossbreeding, producing genetic conditions that cause dwarfism or re-labeling small standard Labradors to something more marketable.
Dogs have been the subjects of artificial selection for thousands of years, creating friendly, capable and attractive breeds. Miniature Labradors are often hybrids: crosses between Labradors and toy dog breeds. Some are inbred or have genetic conditions that stunt their growth. Others are simply standard purebred Labradors that are undersized and do not meet the breed standards. No breed registry recognizes the miniature Labrador as a separate breed or as a size category; the American Kennel Club categorizes Labradors as medium-sized dogs.