Purebred dogs can have a lot of health problems.

•Crippling bone and joint disorders
•Eye diseases that cause reduced sight or total blindness
•Heart diseases that drastically shorten a dog's life
•Hormonal and endocrine system diseases like hypothyroidism and diabetes
•Seizure disorders such as epilepsy
•Skin diseases that cause frantic itching
•Digestive disorders that cause chronic diarrhea and vomiting
•Kidney and liver diseases
•Blood-clotting diseases
•Cancer -- the number-one killer of many, many breeds

Over 300 genetic health problems occur in dogs -- all kinds of dogs, purebred, crossbred, and mixed -- but the risk of these health problems occurring in a purebred dog is higher than in a crossbreed or mixed breed.

Humans have been selectively breeding animals to produce certain traits or visual looks for millenia, in spite of the genetic probems that result from breeding closely related animals.

It is estimated that 50% of German shepards will develop hip displasia, but the breed has many redeeming qualities that make them useful to humans, and few would argue that German shepards don't enjoy thier lives. Spiders have a wobble, but they eat, breed, shed, and don't seem to suffer in any way.