There are numerous dog breeds, with over 800 being recognized by various kennel clubs worldwide. As all dog breeds have been derived from mixed-breed dog populations, the term "purebred" has meaning only with respect to a certain number of generations. Many dogs, especially outside the United States of America and Western Europe, belong to no recognized breed A few basic breed types have evolved gradually during the domesticated dog’s relationship with humans over the last 10,000 or more years, but most modern breeds are of relatively recent derivation. Many of these are the product of a deliberate process of artificial selection. Because of this, some breeds are highly specialized, and there is extraordinary morphological diversity across different breeds. Despite these differences, dogs are able to distinguish dogs from other kinds of animal.