Over at Darwin Catholic there has been some discussion of the human influenced evolution of dogs. Seed actually has it right, it is human influenced evolution. Some of the interpretation of the paper which showed an increase in the frequency of 'deleterious' alleles spin the results as suggesting that dogs are beyond the constraints of evolution. But, as I pointed out over at DC's weblog dogs are evolved toward their own special adaptations, and the lack of these adaptations in their wild cousins is not evidence that wolves carry "deleterious" traits. For me, the most fascinating case of dog evolution is the possibility that they can read human faces. Their wild cousins can not do this, and in fact, it seems that man's best friend is better at this then his closest relative, the chimpanzee. Now, we don't think that wolves are "unevolved" because they don't have the capability to read human faces, they obviously didn't need to in the past. Similarly, dogs do not need functional constraint, that is strong selection maintaining a fixed form of an allele, on many loci because it does not impinge upon their fitness. Not being able to read human faces, or doing the "puppy thang" very well does have a negative impact on their reproductive output. To analogize with humans, just because reheaded individuals have lost function on the MC1R locus, and so are rendered very fair and susceptible to skin cancers as well as hypersensitive toward pain, does not mean they are maladapted. Rather, when you move an allele out of its evolutionarily shaped background its fitness may shift, obviously evolution did not anticipate that thousands of years into the future Europeans would resettle at lower latitudes (remember that almost the whole of the United States is to the south of Europe). The same sort of logic in relation to fitness allows us to infer things which should allow us to interpret the historical record better. For example, DC observes the negative correlation between fecundity and high socioeconomic status in the contemporary period, but, it seems clear that this is a recent phenomenon, otherwise we would not crave high socioeconomic status vis-a-vis our peers. In fact, the historical record, as documented in Mother Nature by Sarah Hrdy, suggests that until the last half of the 19th century elite women in Europe were literally baby machines in relation to their social inferiors. Primogeniture resulted in the reality that the broad mass of society was derived in large part from elites past, while the lower and working classes barely reproduced themselves as their slots were taken over by the younger offspring of the fecund nobility and gentry (in some societies slaves and the lower classes were punished for reproducing!).
Related: JP makes a similar point.
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I'm convinced that dogs can read not only human faces but human emotions (and I don't mean only in the presence of overt behaviors signifying given emotions, e.g., laughing, "temper tantrums").
Despite watching and participating in untold numbers of evolution vs. creation "debates," I have never seen anyone ask a creationist to explain the remarkable diversity of dogs (all of which can of course breed with wolves as well as each other). Then again, despite domestication of canines being a relatively new phenomenon, it has in al likelihood persisted for longer than 6,000 years.
Your post was a good reminder that the term "deleterious" as applied to mutations and the phenotypic changes they produce is strictly relative. In the case of a dog, the presence of a doting human is simply one more environmental change, and of course a powerful one.
The deleterious genes are not imaginary -- lots of purebred breeds have characteristic health problems which can be pretty bad. But on the net, adaptation to the human environment, for example by cuteness, overrides the other problems.
A lot of dog breeds (shar-pei, shih-tzu, chihuahua, Italiand Greyhound) are the biological equivalent of Britney Spears, come to think of it. Their ecological niche is in the human psyche.
There's a paper I read claiming that dogs are lifelong juveniles (like axolotls) who bond to humans the way puppies bond to their mothers. The face-reading might be a development of mom-reading.
The deleterious genes are not imaginary -- lots of purebred breeds have characteristic health problems which can be pretty bad.
the problems with pure breds are two fold:
1) in breeding
2) selecting for extreme traits tends to have negative byproducts
also, yes, dogs are quite juvenille in relation to wolves.
I seem to recall reading that Siamese cats have been selected so strongly for narrow hips (which I guess is considered one of the attractive things about the breed) that some of the pure bred females cannot give natural birth and have to be delivered by c-section. Talk about a characteristics that only make sense in symbiosis with doting humans.
On the creationist issue, I noticed Dembski had gone and linked to an article about this, and the commentors there were all claiming that this proved that genetic diversity had built up among dogs too quickly to be the product of random forces only. Thus going to show that with sufficient determination someone can claim that absolutely everything supports his position, even stuff that appears to directly contradict it.
and the commentors there were all claiming that this proved that genetic diversity had built up among dogs too quickly to be the product of random forces only
well, to some extent the diversity was already in the genetic background. also, there have been widespread gene duplication events in this lineage, so we're not just talking sequence changes.
as for your point about siamese cats, yes, 'antagonistic pleiotropy' is a common feature of powerful directional selection on one trait. we usually notice when it starts to strongly impact survivorship or reproductive fitness.
Given the huge variation in dog sizes, shapes, behaviors, etc., I've often wondered if dogs had something in their genome that just allowed for greater 'plasticity' or something. You see a lot of variation in color and size of wolves. Some other domestic animals share this astonishing range of shapes, sizes, and colors and but most don't. Horses and cattle have been domesticated for a long time, yet aside from variations in colors, they're all shaped pretty much the same as other horses and cattle. Cats also seem not to have the same plasticity in shapes that dogs do. Yet various domestic pigeons and goldfish breeds show such bizarrely different shapes that most casual observers cannot believe they are the same species. Anybody have any thoughts?
Another thing that's always intrigued me about dogs is that unlike other domesticated animals there doesn't seem to be a true 'reversion to wild type' in feral populations. Feral cats or feral pigeons all very quickly look pretty much like their wild ancestors in relatively few generation removed from man's selective breeding. Yet most feral dog populations quickly revert to a medium-sized, short-coated, yellowish dog - the so-called "Pariah Dog" that's found in so many places around the world - why don't the feral populations look more like their wolf ancestors?
Yet various domestic pigeons and goldfish breeds show such bizarrely different shapes that most casual observers cannot believe they are the same species. Anybody have any thoughts?
go to pubmed and look up gene duplication in dogs. that is a reason that is given by some.
why don't the feral populations look more like their wolf ancestors?
one could give many speculative reasons, but perhaps this species can only shift back toward a different adaptive genetic/ecological optimum. also, who knows if the eurasian wolf hasn't evolved over the last 10-15 K?
Perhaps there was more variation in wolf populations in the past than there is now. The wolf we know best, the Timber wolf, is a northern forest wolf. Besides this, I don't know how reliable the Wiki is, but it claims that the almost-extinct Indian Wolf played a considerable role in dog breeding. In what I looked at, there's a lot of doubt about the date and place of domestications, with suggestions of multiple events and a lot of interbreeding with wolves.
http://nationalzoo.si.edu/ConservationAndScience/SpotlightOnScience/fle…>Indian wolf
Indian Wolf
This is a little late but there is this interesting book out (of which I can't find the exact title) which hypothesizes that the actual dog species is the Pariah Dog. This animal adapted as a species to human settlements much like the house mouse or rat. Its pretty fascinating reading if a little nutty at times but his behavioral analysis seems right on. I'll see if I can find the book name.