I'm going to be coming out with a new post in my Evolution series later this week, but in the meantime, for those of you haven't seen them, I'm reposting my first two Evolution posts, beginning with the one that started the series: The Curious Case of Dogs.
Man's best friend is much more than a household companion - for centuries, artificial selection in dogs has made them prime examples of the possibilities of evolution. A century and a half ago, Charles Darwin recognized how the incredibly diverse dogs supported his revolutionary theory in his famous book On The Origin Of Species. At the time, he believed that dogs varied so much that they must have been domesticated from multiple canine species. Even still, he speculated that:
if... it could be shown that the greyhound, bloodhound, terrier, spaniel and bull-dog, which we all know propagate their kind truly, were the offspring of any single species, then such facts would have great weight in making us doubt about the immutability of the many closely allied natural species
If only Darwin knew what we know now, that indeed, all dogs did descend from one species!
While humans have been breeding dogs for over ten thousand years, it was until recently that strict standards and the emphasis on "purebreds" has led to over 400 different breeds that are some of the best examples of the power of selection. Those that doubt whether small variations in traits can lead to large levels of diversity clearly haven't compared a Pug to a Great Dane - I mean, just look at them compared to their ancestor:
We've turned a fine-tuned hunting animal, the wolf, into a wide variety of creatures, from the wolf-looking shepherds to the bizarre toy breeds. Before domestication, dog's life was tough. But when people pulled specific wolves out of their packs and began breeding them, we changed everything. There were some traits that made this easy - the social structure of wolves, for example, made them predisposed to belonging to a community. Still, we opened up a number of genetic traits and allowed them to express variety that would have been fatal in the wild. We not only allowed these traits to persist, we encouraged them. We picked dogs that were less aggressive or looked unique. And in doing so, we spurred on rapid diversification and evolution in an unbelievable way.
Take their skulls, for example. Like other members of the order Carnivora, dog's skulls have a few distinctive characteristics: relatively large brains and a larger-than-normal structure called a zygomatic arch which allows for bite power and chewing. But years of hand-picked puppies has led to an amazing amount of skull diversity in dogs. A study recently compared the positions of 50 recognizable points on the skulls of dogs and compared them to each other and other members of the order Carnivora. There was as much variety in the shape of the skulls of dogs as in the entire rest of the order, and the extremes were further apart. 
What does that mean, exactly? It means that the differences between the skulls of that Pug and Great Dane I mentioned before (on R) are greater than the differences between the skulls of a weasel and a walrus. Much of this variation is outside the range of the rest of the order, meaning dogs' skull shapes are entirely unique. In just a few centuries, our choices have created unbelievable variety in the heads of dogs - more than 60 million years has created in the rest of the carnivores.
The amazing diversity of dogs is a testimonial to the possibilities of selection. And it's not just their skulls that vary. A joint venture between the University of Washington and the Veterinary School at UC Davis mapped the variation in the genomes of a mere 10 different breeds of dogs. They found that at least 155 different regions of the dog's genome show evidence of strong artificial selection. 
Each region contained, on average, 11 genes, so it's harder to identify exactly what about each area was under the most selection, though there were clues. About 2/3 of these areas contain genes that were uniquely modified in only one or two breeds, suggesting they contain genes that are highly breed-restricted like the skin wrinkling in the Shar-Pei. Another 16 had variations in 5 or more breeds, suggesting they encode for traits that are altered in every breed, like coat and size.
While we usually think of evolution as a slow and gradual process, dogs reveal that incredible amounts of diversity can arise very quickly, especially when selective pressures are very, very strong. It's not hard to see how selection could lead to the differentiation of species - just look at the breeds of dogs that exist today. There's a reason that you don't see many Chihuahua/Saint Bernard mixes: while it's entirely possible for their genetics to mix, it's just physically difficult for these two breeds to actually do it. Just imagine what a poor Chihuahua female would have to endure to give birth to such a mix, or how hard it would be for male Chihuahua to mount a female Saint Bernard. Indeed, dogs are well on their way to speciation.
Of course, it's at this point that I have to mention that while I have talked about "dogs" this entire time, they're not actually a different species. Wolves are Canis lupus, while dogs are merely a subspecies of wolves, Canis lupus familiaris. Despite centuries of selective breeding and the vast array of physical differences, dogs are still able to breed with their ancestors.
When you take away the selective breeding done by humans, a number of these unique traits disappear. But feral dogs don't just become wolves again - their behaviors and even looks depend greatly on the ecological pressures that surround them. Our centuries of selective breeding have opened a wide variety of traits, both physical and behavioral, that may help a stray dog survive and breed.
A good example of what happens to dogs when people are taken out of the picture can be found in Russia's capital city. Feral dogs have been running around Moscow for at least 150 years. These aren't just lost pets that band together - these dogs been on their own for awhile, and indeed, any poor, abandoned domesticated canine will meet an unfortunate fate at the hands of these territorial streetwalkers. Moscow's dogs have lost traits like spotted coloration, wagging tails and friendliness that distinguish domesticated dogs from wolves - but they haven't become them. The struggle to survive is tough for a stray, and only an estimated 3% ever breed. This strong selective pressure has led them to evolve into four distinct behavioral types, according to biologist Andrei Poyarkov who has studied the dogs for the past 30 years. There are guard dogs, who follow around security personnel, treating them as the alpha leaders of their packs. Others, called scavengers, have evolved completely different behaviors, preferring to roam the city for garbage instead of interacting with people. The most wolf-like dogs are referred to as wild dogs, and they hunt whatever they can find including cats and mice.
But the last group of Moscow's dogs is by far the most amazing. They are the beggars, for obvious reasons. In these packs, the alpha isn't the best hunter or strongest, it's the smartest. The most impressive beggars, however, get their own title: 'metro dogs'. They rely on scraps of food from the daily commuters who travel the public transportation system. To do so, the dogs have learned to navigate the subway. They know stops by name, and integrate a number of specific stations into their territories.
This dramatic shift from the survival of the fittest to the survival of the smartest has changed how Moscow's dogs interact with humans and with each other. Beggars are rarely hit by cars, as they have learned to cross the streets when people do. They've even been seen waiting for a green light when no pedestrians are crossing, suggesting that they have actually learned to recognize the green walking man image of the crosswalk signal. Also, there are fewer "pack wars" that once were commonplace between Moscow's stray canines, some of which used to last for months. However, they remain vigilant against the wild dogs and wolves that live on the outskirts of the city - rarely, if ever, are they permitted into Moscow. When politicians thought to remove the dogs, their use as a buffer against these animals was cited as a strong reason not to disturb them.
Moscow's exemplary dogs show how different traits help dogs adapt to different ecological niches - whether it be brute strength for hunting in the truly feral wild dogs or intelligence in the almost-domesticated beggars. Some wonder if the strong selection for intellect will make Moscow's metro dogs into another species all together, if left to their own devices.
Dogs make it easy to understand and demonstrate the core principles of evolution - variation and selection - and how they can make such a dramatic impact on an animal. It's no wonder that Darwin took cues from domesticated animals when formulating his theory of evolution. However, there's still a lot to learn about the processes that have shaped our best friends, and what future lies for them. How much time will it take to completely separate dogs from wolves, into their own species? What areas of the genome are key to doing so? In studying dogs and wolves, we may gain insight into how speciation occurs and when a threshold of change is met for it to do so. Seeing how much change has occurred already makes you wonder what surprises our canine companions still have in store for us as they, and we, continue to evolve together over the next ten thousand years.
Citations:
Drake, A., & Klingenberg, C. (2010). Large Scale Diversification of Skull Shape in Domestic Dogs: Disparity and Modularity The American Naturalist DOI: 10.1086/650372
Akey, J., Ruhe, A., Akey, D., Wong, A., Connelly, C., Madeoy, J., Nicholas, T., & Neff, M. (2010). Tracking footprints of artificial selection in the dog genome Proceedings of the National Academy of Sciences, 107 (3), 1160-1165 DOI: 10.1073/pnas.0909918107
Poyarkov, A.D., Vereshchagin, A.O., Goryachev, G.S., et al., Census and Population Parameters of Stray Dogs in Moscow, Zhivotnye v gorode: Mat-ly nauchno-prakt. konf. (Proc. Scientific and Practical Conf. Animals in the City ), Moscow, 2000, pp. 84 87.
Vereshchagin, A.O., Poyarkov, A.D., Rusov, P.V., et al., Census of Free-Ranging and Stray Animals (Dogs) in the Coty of Moscow in 2006, Problemy issledovanii domashnei sobaki: Mat-ly soveshch (Proc. Conf. on Problems in Studies on the Domestic Dog), Moscow, 2006, pp. 95 114.
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Then there's that little experiment in Russia where foxes were selected for the more docile of the group. After a few generations they lost their musk, and started to develop fur patterns, colors, etc.
In essence becoming very dog like.
And then there's the accidental discovery at I believe Brown University where some bacteria evolved to digest the medium that they're grown in versus their normal foodstuff.
To a non-expert who loves dogs and always wonders how their higher level behavior resembles even our own, this is an incredible read. Thank you.
Thanks Christie.
I will use this as an example of the potential variation in living things for my Biology class.
Was about to ask for vision of the Moscow dogs, but YouTube came to the rescue:
http://www.youtube.com/watch?v=fPi7tIm9tj4
"Just imagine what a poor Chihuahua female would have to endure to give birth to such a mix, or how hard it would be for male Chihuahua to mount a female Saint Bernard. Indeed, dogs are well on their way to speciation."
Artificial insemination. It might be interesting to see what would happen if a cross was made between those breeds of dogs whose skull morphology (or other characteristics) diverge the most. We might get some interesting insights into how genes control development....
> how hard it would be for male Chihuahua to mount a female Saint Bernard.
Ummm, I've actually seen something very much like this. Back in my immediately post student days, a house mate had a female Great Dane while the neighbor had a male miniature terrier who used to get under the fence and come over to play every so often.
Anyway, one day we were sitting in the back yard having a beer and ....
How did they manage it? The Great Dane - who was in heat - lay down. Not too hard really.
I found this article particularly intriguing because I have never really thought about how varied dogs are. I find it surprising that a wolf could evolve into so many types of dogs! It is interesting that because wolves were used to communities, dogs that are living in a family setting arenât going against dogâs nature. It amazes me how much we have contributed to the evolution of dogs! I particularly liked the section you included on skull structure on different types of dogs. It is weird that the same species could have such a range in skull structure. How strange would it be if humans also had this variety of skull shapes? This post made me realize how much we actually are involved in evolution, and how we have the power to effect the evolution of another species by gene selection and careful breeding. It is interesting that without human intervention, some dogs traits would disappear. The fact that dogs in Moscow have learned to cross streets is astonishing. Dogs have really adapted to their surroundings. I also wonder what is in the years to come for the evolution of these smart animals. This is a great topic to explore, and I really like the background and facts you included about this topic.
Where I live, in south central Denver, foxes have been evolving rapidly into a behaviorally and physically different animal from their country cousins. After being acquired from European stock for their docility and dark silver-black fur, these foxes were simply let loose by bankrupt fur breeders many decades ago, according to an article in the Rocky Mountain News.
This release coincided with the arrival of a non-indigenous squirrel which is found in our city in vast numbers, and ever increasing numbers of Canadian Geese which populate our golf courses and park ponds year round, and provide an abundance of eggs, the favorite food of our local foxes.
Foxes with patchy spots seem to have always been most docile around humans, and those who are comfortable living near humans have had a never ending supply of squirrels but these squirrels can only be caught during daylight hours when they come down from the trees. The foxes then, must be out in the open and visible to humans in order to capture squirrels, and the friendliest of foxes can flourish within a small territory, which often leads to humans feeding them additional meals.
Is this natural selection at work? I think so. For at least five years, our neighborhood had a population of dozens of multi-colored foxes who would even catch balls when thrown at them (although they did not return them) and then come back for more balls. One fox slept on a neighborhood porch in the shade of a rabbit hutch containing an untouched pet, near where the owner provided a daily egg breakfast for the fox. They were famously interested in listening to classical music, and would sometimes show up for free vocal concerts by a folksinger.
People would drive to our neighborhood just to watch the foxes play and lounge right out in the front yards of this area. They were subjects of hundreds of photos and videos, and there were no negative incidents reported regarding fox-human interaction, although we all knew it was only a matter of time.
When a hysterical property owner trapped and killed a large number of foxes on her forested estate, a few years ago, the dozens of new neighborhood foxes which quickly replaced them were of the more typical red color, and were far more nocturnal and shy. The difference in their behavior is stunning, and these redder foxes are more aggressively defensive with neighborhood pets, and they are careful to avoid being seen by humans.
The commonly shared opinion in our neighborhood is that the old and new fox groups are a very different breed, the earlier group being a self-selected dog-like breed which was on it's way to becoming something like the deliberately domesticated Siberian foxes.
Some of the more domesticated group did manage to avoid being trapped and gassed and have moved on to other neighborhoods, but we rarely hear of any Denver foxes as outrageously domesticated as the originals.
So, if dogs provide evidence of evolution, you know, Darwin's "origin of species"---where is the new species? It seems that, after all of the natural selection we pushed species A with, we end up with...species A. Where is species B that should have originated from species A? It seems that we've only explored the incredibly large and diverse gene pool of one species.
Great article! I particularly enjoyed the portion about Moscow's dogs and how the smartest dogs become the pack leaders. It reminds me the sequel to Ender's Game; a book called Ender's Shadow, in the beginning of which the homeless children begin to form themselves into families and the smartest ones, or the ones who can provide the food, become the leaders. Very interesting article.
Overall, I find this to be a very interesting article. Particularly, I find the topic regarding the Moscow Metro dogs to be extremely interesting, as it gives mankind insight as to how the product of mankind (domesticated dogs) will act when humans no longer are in a ruling position of authority.
Earlier, before reading this post, I viewed a program on the Discovery Channel regarding what would happen to the Earth if man were suddenly to vanish one day. The show seemed to predict that while housecats would evolve to better fit their new environments, domesticated dogs would revert back to the habits of their ancestors in order to survive because they are more relatively fit to fend for themselves. Some of the Moscow street-dogs, in a way, demonstrate this prediction in the way that the âwild dogsâ and âscavengersâ succumb to a pack mentality amongst them. This ideology also involves marking and defending territory against other competing groups.
Additionally, the point in the post where it explains that many citizens of Moscow argue that the feral dogs should not be removed because they provide a buffer zone against the wolves that inhabit the outskirts of the city. This fact really struck me as it almost suggested that, in a way, manâs creation was still doing manâs bidding even if not under the direct control of mankind. It is as if man created his own problem (warring, stray dogs) to shield itself from its long-time problem of attacking wolves. The fundamental challenge that humans have faced for centuries has been erased due to its own creation. This ceases to amaze me.
Finally, and perhaps most relevantly, it is revealed that the âbeggar dogsâ, those that spend time in populated, human areas in hopes of getting charity scraps of food, are some of the most successful of the wild dogs of Moscow. Perhaps this fact is the most evident of human involvement in the domestication of canines. The idea that a wolf coming from a tough world that merits strength, speed, and murderous skill can become a dog that uses his mind and wit over all else to be successful may truly reflect that they still live in a world ruled by man.
This is a land where the strong may be given blatant glory, but the smart control everything. The dogs of Moscow display all of what humans have created on Earth. The diversity we find fascinating, the values we recognize, and the brutal steps we take to ensure security are present in the wild manifestation of man found in the canines that roam the streets of mankindâs dominion.
To #8: speciation is a process. Two groups of animals are defined as being of different species based on lack of interbreeding, not only on genetic incompatibility. Really, the only reason that a great dane and a chihuahua are not defined as two species is that they are each quite able to interbreed with intermediate breeds, thus keeping "dogs" as a singular species. Arguably, if all breeds except the giant breeds and the toy breeds were to die out, we might well have to define "large dogs" and "small dogs" as two different species, because they would no longer be able to interbreed without help.
But the human definition is the less interesting aspect of the process. More importantly, once two groups stop interbreeding, they lose any selective pressure to stay interfertile, in a purely genetic sense. At that point, the fact that they don't breed (because of geographical or physical barriers) is slowly backed up by the random accumulation of genetic changes that eventually means they can't interbreed to produce fertile offspring, or any offspring at all. At that point, there's essentially no going back.
Why don't we define species based on their genetic incompatibility? Well, if so, we'd have to define cows and buffalo as the same species. Also, because their hybrids (ligers and tigons) are occasionally fertile, we'd have to define lions and tigers as the same species, as well as false killer whales and dolphin, due to the fertility of the Wholfin. Never mind that the hybrids only occur in captivity, and that the parents are hugely different...they retain enough similarity from their shared ancestry to muddy the waters.
Again: we are looking at a process, and this is a snapshot of one point in the process. Some dog breeds are actually becoming less inter-fertile / more inter-sterile, BTW, presumably due to some of the genes in the fast-evolving, artificially-selected regions of the genome, as described in the article.
Hope the context is helpful.
An interesting related paper about the relatively high mutation rate in Canidae:
http://jhered.oxfordjournals.org/content/98/5/452.full
On the topic "Just imagine what a poor Chihuahua female would have to endure to give birth to such a mix", the uterine structure of the uterus would restrict the size of the developing fetus. That's how horses and ponies handle it. More developmental epigenetics (in the original sense of Waddington) than genetics.
Has anyone noticed that you can substitute "human" for "dog" in this aricle without much discord? The variety in size in humans is actually quite amazing, as well as specialties (sports) and adaptation to climate.
Great read. Thank you for posting. I look forward to more like this.
Fascinating. Has anyone studied if the stray cats who become good at begging meals from surrounding human communities are undergoing any similar sort of change?
I particularly liked the section you included on skull structure on different types of dogs.
Why do you insist on calling all the dogs one species? It's clear to me that if tigers and lions are different species (despite interbreeding) then Chihuahuas and St.Bernards are different species.
This also opens the door for humans. Are we humans a single species? Why? Perhaps, despite the fact of interbreeding, black and whites are different species? Also interbreeding is not always established. Nobody tried to breed pygmies and Asians, for example, so we don't know if pygmies are humans or different species of hominids.
I know all this is extremely politically incorrect, but you gotta admit these are interesting questions.
Un interesante artÃculo, muy recomendable. Felicitaciones a la autora. Saludos:
Alejandro Ãlvarez
Change is the only constant thing in this world and we have traced it way back in time. Evolution is a way of oping up with the changing world. And even dogs evolves. They have been cross breed and this is the outcome. What you have shared is a helpful and informative one. More power and thanks a lot.
"This dramatic shift from the survival of the fittest to the survival of the smartest ...."
It's not a shift at all. Fitness is meaningless without a context, and this is a context where smartness is an element of fitness: where a clever dog fits its task better than a stupid one.
I think that what fascinates me as much as this is that the domesticating wolf actually assisted human evolution from hunter/gathering to agrarian by providing a "perimeter guard" against predators. The wolves had an interest in making sure that their scraps from the humans continued and this gave our ancestors a bit more time to start pondering about the meaning of life; or to start thinking and planning. It gave them time to become storytellers, and to start taking active control over their environment.
In short, the domestication of wolves has led to AGW.
Finally, and perhaps most relevantly, it is revealed that the âbeggar dogsâ, those that spend time in populated, human areas in hopes of getting charity scraps of food, are some of the most successful of the wild dogs of Moscow. Perhaps this fact is the most evident of human involvement in the domestication of canines. The idea that a wolf coming from a tough world that merits strength, speed, and murderous skill can become a dog that uses his mind and wit over all else to be successful may truly reflect that they still live in a world ruled by man.
Why do you insist on calling all the dogs one species? It's clear to me that if tigers and lions are different species (despite interbreeding) then Chihuahuas and St.Bernards are different species.
This also opens the door for humans. Are we humans a single species? Why? Perhaps, despite the fact of interbreeding, black and whites are different species? Also interbreeding is not always established. Nobody tried to breed pygmies and Asians, for example, so we don't know if pygmies are humans or different species of hominids.
I know all this is extremely politically incorrect, but you gotta admit these are interesting questions ı am learn
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