Monday, February 22, 2010

Another version of the naturalistic fallacy in the quest for longevity.

 photo credit; national park service
It is not unusual for promoters of raw diets such as BARF and "natural" diets like the evolution diet to claim that wild animals are much longer lived than domestic animals, especially when they are fed commercial dry food. The culprits in kibble are variously claimed to be "diseased" animals, grains, or various preservatives or unnamed "toxins". Similar claims for longevity in wild animals in their natural habitats are often made by promoters of various types of "natural" medicine such as herbal and homeopathic remedies.  These claims have always struck me as rather silly, so I thought it might be interesting to look at some longevity data for different species in the wild and in captivity, what they are fed in captivity, and how their longevity compares to closely related domestic animals. It might also be interesting to consider how humans and especially dogs have evolved together and how cooking and/or processing food has influenced that evolution.

It is sometimes difficult to evaluate the longevity of animals in the wild, but we do have excellent records of wild wolves in Yellowstone National Park since their reintroduction in 1995. The Yellowstone wolves have been closely monitored and studied for 15 years now, and we have data on hundreds of yellowstone wolves.
The 2008 Annual Report of the Yellowstone Wolf Project lists all known cases of mortality and the ages at mortality and the oldest surviving wolves in Yellowstone. Pup mortality has ranged from 0 to 71%, but seems to average about 50%. Periodic outbreaks of canine distemper virus seem to be responsible for years with higher pup mortality. For wolves that survive to adulthood, adults are considered "old" at greater then 5 years. At the time the 2008 report was written, wolf # 192M of the Belcher Pack was nearing 12 years of age and was the oldest known Yellowstone wolf. There were also at least two other notably old wolves alive at the time that were 11 years old. The average lifespan of a Yellow stone wolf is about 4 years. Longevity records for wolves in captivity indicate that wolves in captivity can live up to 20 years, and the oldest record in the wild is 16 years. Wild wolves die of intraspecific aggression (killed in conflict with other wolves), injuries, disease, and malnutrition. Wolves in captivity (and domestic dogs) do not tend to die of the same things-they live long enough to suffer from the diseases of old age-degenerative joint disease, cancer, etc. Wild wolves (with the exception of some endangered subspecies such as the Mexican wolf and the Red wolf) may have more genetic diversity than most domestic dogs as well, which may reduce the incidence of certain types of cancer in wolves compared to some inbred breeds of dogs independent of diet.

Since wolves in captivity live longer than wild wolves (and possibly longer than comparably sized domestic dogs) , what is the recommended diet for captive wolves? The husbandry chapters of the Nutrition Advisory Group of the American Zoo and Aquarium Association seem to recommend dry, commercial dog food as the primary source of food for captive wolves. (here, here, and here). There is also some evidence that the dental hygiene of captive wolves is better when fed commercial dry dog food then when fed a raw meat diet supplemented with bone meal and vitamin and mineral supplements. These recommendations indicate that professional zoologists and zoo veterinarians find commercial diets superior to raw meat diets for several reasons. Bones and whole prey may be given for behavioral enrichment,  or to help transition wolves to predation in reintroduction projects, but ordinary dog food is perfectly adequate to maintain wolves in captivity and avoids problems associated with nutritional imbalances, bacterial contamination and spoilage.

The situation in cats is similar, although records for longevity for small cats (genus Felis) in the wild appear to be similar to the records for captivity. This may be because small cats tend to eat small prey that is not as likely to injure the predator and are not as subject to attack by neighboring cats . Average lifespans of cats in the wild are probably much lower than domestic cats due to disease, injury and starvation, despite the potential for small wild cats to live as long as their captive counterparts. Zoo standards for keeping small felines also indicate that commercial dry cat food is the preferred maintenance food in zoos, with whole prey reserved for behavioral enrichment purposes.

Finally, I would also like to address the idea that raw food is better because humans evolved eating raw food. While this is obviously true to a point,there are recent discoveries in Africa indicating use of controlled fire as early as 2 million years ago and the hypothesis that cooking made more types of food available and digestible to early human species and drastically influenced human social structure, reproduction and body size. As early humans (Homo erectus, neandertalensis and sapiens) spread out of Africa, their ability to do so and their success depended on cooking and the use of fire. It appears that dogs were domesticated much later,  separating form wolves 15-30 thousand years ago. Part of this evolution probably involved wolves or early dogs scavenging waste and food scraps from trash heaps. The separation of dogs from wolves also seems to be related to the advent of agriculture, which means food surpluses in the form of grain and possibly root vegetables which need to be cooked or otherwise processed for digestion by humans and dogs. Cooked food may well have been important to both human and canine evolution and may have a lot to do with why we are human and dogs are not wolves in the first place.

The science behind human and animal nutrition, and the increasing knowledge of how cooking has influenced human evolution, first with cooking of wild foods, and later with the development of agriculture is fascinating. It stands in stark contrast to the vitalism and pseudoscience produced by the raw food supporters. Animal lifespans in the wild are generally much shorter than those of domestic or captive animals. While wild animals tend to die of injury, malnutrition or infectious disease before they get a chance to get cancer, there is no evidence that good quality commercial diets or cooked food cause disease in pets. The varying incidence of various cancers in different breeds would indicate again that many of the diseases which raw diets are supposed to prevent have a strong genetic component. Changes in kennel club breeding practices eliminating the severe inbreeding present in so many breeds is likely to benefit pet health more than a raw diet or a pseudoscientific "evolution diet" ever will. Claims that wild relatives of domestic animals live longer than the domesticated species do are demonstrably false, and the idea that raw food or some other type of "evolution" diet will extend lifespan appear groundless.