Dogs are inherently unnatural. Any dog bred by humans. An akita is very close to a wolf but yet lives only 12 years. A cocker spaniel is no where near any wild canine and yet frequently live to 16+ years. Should longevity be purposefully bred into all breeds? Likely yes, but its not. The dog is bred for a purpose. All dogs breeds have been bred for a purpose. Whether it be lap dog, herder, protection, hunting in various forms (sight, point, retreive, etc...) They are better more often for a specific job than an unplanned dog.
A poor sire in nature can also be a malformed animal. It's rather hard to be in better health when your legs are crooked. I do not believe sickness is the only criteria. Evolution doesnt work that way.
I LOVE to see the science behind 'all dogs are unnatural'. Dogs naturally developed from wolves through a natural evolutionary process. They willingly followed humans as we were an easy source of food. We then bred different breeds depending on OUR needs thus forming the various breeds, interfering with Nature's process of weeding out the weaker dogs, interfering with the pack structure that often determined who breeds and who doesn't (Alpha Male, Alpha Female =the stronger, physically fitter individuals).
An Akita being CLOSE to a wolf, at least in looks doesn't mean anything but thanks for bringing that up. Japanese Akitas in pre-WW2 Japan were a lot more long lived. The Akitas of today, especially the American variety are bred again from a very limited genetic stock. They were almost extinct in Japan as they were used for their fur which lined the inside of soldiers coats. Which further proves my point that smaller genetic pools, lead to shorter lifespans and genetically weaker offspring.
As for the Cocker Spaniel, it's an old working breed. OLD meaning that it developed at a time when dogs were kept outside, often allowed to roam free and choose their own mates. The breed went through a natural stage of development. Those breeds tend to be the healthiest. More recent breeds coming out of purposeful design are less heathy.
Now unto the 'malformed' animal part. A malformed pack animal in nature is less likely to breed. Its malformed descendants, unless they take advantage of a niche environment that suits their deformity will also be less likely to survive. Crooked legs breeds are created by humans, so are all brachycephalic breeds. In fact, anything not resembling a dingo, a Congolese Basenji (not the American AKC type) and generally a pariah type dog has been bred by humans who often mess up the dog's genetics.
And yes, evolution does not work with health as the ONLY criteria, the environment, availability of resources, adaptation to those conditions, availability of individuals for reproduction also play a role. But the viability of one's offspring is a major driving force. I don't suppose the original Shar Pei (Bone Mouth Shar Pei) would have faired very far in its current American wrinkly form plagued by entropion, fever and a host of other breed specific, debilitating conditions. Those individuals expressing those extreme traits would have vanished unless their environment favored them. As is the case here where they have been bred to look a certain way with food secured by their owners. They no longer have to hunt, eye sight is not a life or death factor, so those folds covering their eyes are not a life or death factor.
So to get back to my original point: 'Muts' is a word used in arrogance. Breeds, are all endogamous 'muts'. There is no issue, in my opinion, crossing different breeds (healthy individuals only). This is how our breeds came about. Most of them as it turns out, suffering from very specific ailments. I'd like to see less self-righteous rage. Less looking down on others. We can love our breed without hating others.
