A recent genetic study in PLoS Genetics has some interesting implications relating to claims made by some dog breeders and many practitioners of alternative veterinary medicine. As our ability to collect and analyze large amounts of genetic data improves, we can learn a lot about how genetics affect the susceptibility of dogs and humans to various diseases. The genetic history of the domestic dog is at least 15,000years, and possibly as much as 100,000 years. Over most of this time, dogs were used for a variety of work including hunting, herding, guarding, and as pets, but breeding practices were haphazard and mixing between types of dogs and even back to wolves as common.
Basically all modern breeds have been developed in the last 200 years, with many deliberate (small founding populations) and inadvertent (low numbers of dogs during social and political upheavals such as the two world wars) genetic bottlenecks. The history of the Irish Wolfhound is a good example-claims that the breed as it exists today is the same as hounds used in ancient times are not supported by any solid evidence. While it is certain that large sight hounds existed thousands of years ago in the British Isles, the modern breed is the creation of Victorian fanciers who "recreated" the breed in the mid to late 1800's based on their ideas about how the breed should look and on current Victorian ideas of "improving" animals through selective and "pure" breeding.
While these genetic studies are still preliminary, they are starting to identify gene sequences which have been strongly selected for in the process of creating these breeds. These sequences often contain mutations with major effects on both the phenotype of the dogs and on their health. The diseases which some breeds are very susceptible to are often similar to diseases which also occur in humans, and knowledge of dog genetics is applicable to human health as well. As the specific portions of the genome which affect disease susceptibility are identified, we will learn more about how to avoid many of these health problems in the future. Unfortunately for many of the alternative medicine crowd, claims that diseases like cancer are product of vague "toxins" and modern industrial society are unsubstantiated by the evidence. While it is true that pets can develop cancer due to exposure to specific, known toxins such as secondhand smoke, these exposures are fairly well known and documented in both animals and humans, and are often related to the owner's lifestyle choices more than any generic effect of modernity. While avoiding known toxins such as tobacco smoke is always a good idea, trying to improve our chances with supplements or "superfoods" generally does not work the way we would wish it did.
The more we learn about the interaction of our genes with the environment, the more we know that disease is often a result of genetic influences which we can control to some extent in domestic animals.
Claims that cancer and autoimmune diseases are caused by specific diets, vaccines, or undefined toxins remain unsubstantiated, and support for them is getting weaker as we learn more about the genetics of dogs and other species.