Sometimes scientists report on research which clarifies what we already know. 'Survival of the Cutest' Proves Darwin Right:
The study, published in The American Naturalist on January 20, 2010, compared the skull shapes of domestic dogs with those of different species across the order Carnivora, to which dogs belong along with cats, bears, weasels, civets and even seals and walruses.
It found that the skull shapes of domestic dogs varied as much as those of the whole order. It also showed that the extremes of diversity were farther apart in domestic dogs than in the rest of the order. This means, for instance, that a Collie has a skull shape that is more different from that of a Pekingese than the skull shape of the cat is from that of a walrus.
Dr Drake explains: "We usually think of evolution as a slow and gradual process, but the incredible amount of diversity in domestic dogs has originated through selective breeding in just the last few hundred years, and particularly after the modern purebred dog breeds were established in the last 150 years."
Domestic dogs don't live in the wild so they don't have to run after things and kill them -- their food comes out of a tin and the toughest thing they'll ever have to chew is their owner's slippers. So they can get away with a lot of variation that would affect functions such as breathing and chewing and would therefore lead to their extinction.
"Natural selection has been relaxed and replaced with artificial selection for various shapes that breeders favour."
The team divided the dog breeds into categories according to function, such as hunting, herding, guarding and companion dogs. They found the companion (or pet) dogs were more variable than all the other categories put together.
According to Drake, "Dogs are bred for their looks not for doing a job so there is more scope for outlandish variations, which are then able to survive and reproduce."
It is well known that feral dogs don't usually look like Pekingese. Seeing as how strange looking small dogs often evoke hostility on the part of humans who are not their owners, the critical role of their owners in keeping these morphs around is self-evident. By contrast working dogs tend to look more "normal." The difference is like contrasting the haute couture you'd see during fashion week, and the kind of apparel you'd actually wear in real life.
As noted by the researchers above, skull shape is probably the tip of the ice berg. There's a lot of behavioral variation in dogs, no one would confuse a pitbull with a golden. Finally, I think one big picture analogy might be our own species, who are quite possibly self-domesticated....
The paper will be out in a few days in The American Naturalist.
"no one would confuse a pitbull with a golden"
Some years ago, an ordinance banning pit bulls was proposed in Denver. A state's attorney there opined that such a law was _unconstitutional_.
Freak of nature indeed! For the modern, politically correct dog breeds don't really exist--they are just a social construct. The behaviour differences you think you see between breeds are caused by upbringing.
"The behaviour differences you think you see between breeds are caused by upbringing."
I was having a discussion about this the other day in the context of Kagan & Freedman's observations about the behavioural differences of newborn babies, and Freedman's comparison to the different behaviour of pups.
The Freedman research is summarised in an article by the Skeptic editor Frank Miele.
Interesting article, Blumenthal. I was just joking in my earlier post. The personality of dogs varies not only between breeds, but also between individuals of the same breed. I have two pugs who are sisters from the same litter. I have had them since they were 10 weeks old. They have VERY different personalities. I have a Chihuahua who seems to have an IDENTICAL personality to a Chihuahua I had several years ago (both very bossy) I also have 4 children (grown) who all have very different personalities, though they were all brought up the same. I think personality in dogs and people is almost entirely inborn. But if parents realized how powerless they would be to influence their offspring's personality they might be afraid to have a baby at all.
I hate the idea of deliberately breeding animals into freaks. Their own bodies are a burden to them. I am thinking of the various squashed-face dogs, and more recently cats. They can hardly breath and frequently suffer respiratory infections.
To me, this highlights the problem with identifying a difference between "natural" selection and "artificial" selection. I don't think there's a real distinction.
The more important factor here is the intensity of the selection pressure. Selective breeding by humans creates substantial selection pressure on certain traits, which is why such drastic changes occurred over such a small time scale.
Any selection pressure with similar intensity would have a similar result, regardless of its source (eg, "natural" or "artificial", whatever those terms really mean).
Cave Bear remains found in the Drachenhohle show a tendency to odd deviations from the norm in their extremely long snouted skulls, like collies. Others were were bulldog-like
Konrad Lorenz attributed this to "One particular kind of positive feedback when individuals OF THE SAME SPECIES enter into competition among themselves... For many animal species, environmental factors keep... intraspecies selection from [leading to] disaster"
He thought this was analogous to certain changes that the physique and behaviour of humans had begun to show.
Evolution resulting from conscious selection pressure by humans is still evolution, but it's evolution to fit, for example, a cuteness niche in the psyches of certain human individuals. That's a bit different than evolving to dig out badgers or kill rats.
It's a kind of weird co-evolution I suppose. You could probably write a sci-fi story where human females evolved until every one of them had a tiny dog like a shihtzu or sharpei, while at the same time all the other dog breeds died out and the toy dogs were the only ones left, so that finally everywhere you looked there would be women with sharpeis.
I don't think dogs have applied any significant selective pressure on humans (which would be require for true co-evolution). But I might be wrong.