A key factor for many dog owners is how easy their pooch is to train. Darwin’s Ark lets owners register their dogs in a database that records dogs’ behavioral traits alongside their breed type. Border collies are often considered one of the most trainable dog breeds, but that thinking has more to do with confirmation bias than reality. But that information isn’t really useful for determining whether an individual dog will be easy to train. Analysis of guide dog populations shows that when complex behavioral traits are aggressively selected for, the risk of genetic disease in the dog population spikes, says Karlsson.