National Geographic

People and Dogs: A Genetic Love Story

Here’s a possibly true story about the first friendly dog. It’s dusk on a human settlement some ten thousand years ago. After a long day of farming, a family gathers around a campfire. They’re kicking back with hunks of venison (a rare treat), some corn, bread, maybe even a few cups of mead. Suddenly they hear rustling coming from the shadows. They turn around and see the glowing eyes of a wolf.

The people are surprised, maybe, but not scared. For many years they’ve noticed an odd group of wolves loitering just outside the village, rummaging up food scraps from the dump pile. The animals have never caused any harm and keep to themselves. But this is the first time a wolf has dared to come so close. It slowly approaches the fire, sits down, and cocks its head. Somebody tosses out a bit of bread.

As a recent dog owner, I love this story: Dogs are the wolves that mooched. They needed us, approached us, and ultimately wooed us into being best friends forever. This is a popular scientific theory — the ‘scavenger hypothesis’ — of how dogs came to be. But it’s not the only one, not by a long shot.

Treats, do you have treats?!

Another theory says that people went out into the woods and deliberately trapped wolf pups, with the goal of training them to be sentinels or hunters. Still other scholars say the co-evolution of wolves and humans was mutually beneficial, with humans learning to hunt by watching wolves. “There are as many specific scenarios as there are people working in this field,” says Bob Wayne, professor of evolutionary biology at the University of California, Los Angeles. “We’re looking back at such a long time ago, it’s a matter of speculation.”

Most genetic evidence says that dogs emerged in the neolithic period, just as humans were transitioning from a hunter-gather lifestyle to one of agricultural settlements. But some dog fossils are much older, dating as far back as 33,000 years ago. Where canine domestication happened is also up for grabs. It could have been in the Middle East, China, Siberia or several places at once.

Erik Axelsson and colleagues at Uppsala University in Sweden tried to learn more about the evolution of canines by comparing the genetic sequences of modern-day dogs and wolves. As they report today in Nature, dogs show distinct differences from wolves in genes involved in two key functions: brain development and starch digestion.

The researchers combined samples from 60 different dogs of 14 different breeds, from the shaggy bearded collie to the super-short drever to the svelte and wolf-like Swedish elkhound. They sequenced different parts of the genome in each one, and then merged them together to create a master ‘dog’ reference. They compared this to a master ‘wolf’ genome based on samples from 12 wolves in seven different countries.

Some 36 regions of the genome carry different variants in dogs and wolves, the study found. Each region is relatively large, encompassing three or four genes, but only one gene in each region is likely responsible for the difference, Axelsson says. Of the 122 candidate genes identified, many have similar biological roles. For example, eight of the genes are involved in the development of the brain and nervous system.

Brain development genes are interesting because of the well-known behavioral differences between dogs and wolves — namely that wolves turn out to be aggressive and dogs don’t.

A wolf pup in the Zürich zoo

“Wolves and dogs are actually quite similar when they’re very young: They both do the same playful behavior, run around in circles, and generally look cute. Little wolf puppies will even bark like a dog,” says Nicholas Dodman, a professor in the veterinary school at Tufts University. “But suddenly the wolf grows up and becomes aloof and lean and suspicious.”

Many animals seem to take on a more juvenile state as they are domesticated, getting bigger eyes, smaller faces and less aggressive demeanors. “One common way of achieving a domesticated form of a species might be to slow down the development of the animal,” Axelsson says. “So the finding here, that it’s the development of the nervous system that’s affected, gives some support to this theory.”

Most of his new study, though, is devoted to digestion genes. Dogs break down starch in three digestive stages, and the researchers found genetic differences related to each. Their strongest example hinges on AMY2B, a gene that in makes alpha-amylase, an enzyme in the pancreas that helps convert starch into maltose. The wolf genome carries 2 copies of AMY2B, whereas dogs carry anywhere from 4 to 30 copies. What’s more, the researchers found that alpha-amylase levels are 28 times higher in pancreatic tissue from dogs and nearly five times higher in blood.

Dogs, in other words, evolved a mechanism for digesting starches that wolves don’t have. “This was the big surprise. No one had anticipated it,” Axelsson says.

Axelsson says his findings fit well with the scavenger hypothesis. If wolves had wanted to get human food, they would have needed to evolve both trusting behaviors and mechanisms for digesting starch. “Selection pressures to change both the behavior and the digestive system may have been happening at the same time,” Axelsson says.

Other experts point out, though, that these changes could have easily come about at different times. It’s possible, even likely, that wolves started hanging around our dumps a few thousand years before we had any starches to speak of. In order to know for sure, future studies will need to compare DNA from a wider range of dog breeds as well as from dog fossils.

Amidst all the speculation, I’m taking two broader points from this study. One’s a practical tip for dog owners. Should you try that trendy (and expensive) raw-meat diet? “This suggests no,” Wayne says. “Dogs have special digestive equipment for handling carbohydrates.”

The second is that dogs can teach us about our own history and genetic evolution. Get this: Human studies suggest that we, too, picked up extra copies of the alpha-amylase gene during the agricultural revolution. “We have evolved, co-evolved, in parallel to the same environmental change, which was the development of agriculture,” Axelsson says. “It makes you realize how big a change it must’ve been.”

*

Illustration by Tony Hall, photos by Flossie Beasley and Tambako the Jaguar

There are 13 Comments. Add Yours.

  1. cynthia allen schenk
    February 1, 2013

    Thanks I love this story and I love my dogs. I really like your publications.

  2. Ed Temple
    February 11, 2013

    After watching neighborhood dogs scavenging loaded Pampers in the garbage cans on the street, I wondered whether dogs/wolves may have been brought into caves during the Ice Age partly to clean up after our ancestors who could then throw the dogs out in the cold to do their business. A symbiotic relationship

  3. Yogurt
    March 10, 2013

    The greatest mistake of mankind, without a shadow of a doubt.

  4. Fernandez
    April 8, 2013

    Hi, I am a not so regular reader but piqued by the cartoon in the header, could you tell me who the artist is and where I can find more?

    thanks a bunch!

  5. Virginia Hughes
    April 8, 2013

    Hi Fernandez,

    The illustration was done by Tony Hall. He has passed away, but his wife posts a lot of his work on Flickr. You can see more here: http://www.flickr.com/photos/libbyhalldogs/with/5417659625/#photo_5417659625

  6. Mike A.
    May 13, 2013

    A poster says, “The greatest mistake of mankind…”

    Hardly. Dogs are an integral part of our history and culture. Hating them is tantamount to hating yourself… IMHO.

  7. joe lane
    May 13, 2013

    I learned early on on life what love was by having a dog. The companionship, belief that your human can do no wrong,the everlasting loyalty is exempary of what true love is all about, and needs to be borne out in human/human contact, which is what life is all about, or should be!

  8. Kevin O’Connell
    May 14, 2013

    There is an old Polish proverb: The greater love is a mother’s, then comes a dog’s, then a sweetheart’s.

  9. Alphonse
    September 8, 2013

    They say that dogs split off from wolves and started to evolve in their own direction about 32 thousand years ago. And human agriculture did not originate before 10 thousand years ago. So humans and primitive dogs must have lived more or less together for about 22 thousand years before they both started to adapt to a more starch rich diet.

    During these years, the dogs must have looked much more like wolves than their later starch adapting descendants.

    As for the theory that humans killed the aggressive wolves and tolerated the more peaceful ones. That’s not impossible, but they don’t need to kill them to affect the selection pressure. They could just as well chase them away, preventing them from coming too close the tribe of hunters and gatherers. The more tame a wolf is, the more trustworthy it is, and the more food it has the chance to get. In a prehistoric world where starving to death was not unusual, every piece of food meant a bigger chance to survive. If more tame wolves found more to eat close human population than the wilder ones, they would have better survival chances, and better chances to pass on their genes to future generations. These new generations would have the genes that separated them from their wilder relatives.
    It is also possible that wolves that for some reason were rejected from their pack were so desperate that they started to follow humans, hoping there could be something to eat. Those lone wolves would now and then be joined by other loners, forming their own packs. These would probably already be different from their relatives, being to small or peaceful to take up competition with the other and more aggressive pack members.

    Why did humans tolerate them? Maybe they were superstitious, or they warned them against wild pack of wolves and other predators. And maybe humans learned to read their signs, knowing when they had gotten the scent of a prey. Perhaps they simply respected each others at first, and then gradually learned to cooperate. The most successful ones also had most success in passing on their genes. Gradually humans would recognize individual animals, maybe having certain favorites among them who were rewarded with a little extra treat now and then (if the humans themselves were starving and decided to kill an animal or two, it’s not likely they would pick their favorites). As mentioned, you don’t have to kill the most aggressive ones, all you have to do is make sure the tamer ones have better survival odds and better chances to reproduce themselves and their offspring, and it’s their genes who will spread in the population.

    If they did live with hunters and gatherers for 22 thousand years, it would most likely have been a constant flow of genes between the wild pack of wolves and the “tame” packs. Probably not that much, and more rarely as time passed by, but I doubt they would be completely isolated. The real dog evolution did not start before the origin of agriculture, when the dogs were already preadapted to live close humans around the first small villages. Among other things, the new diet gave rise to a new kind of selection pressure, and the dog populations became more isolated as in genetic bottlenecks.

  10. Alphonse
    September 8, 2013

    P.S. Not to mention that it is a lot easier to do selective breeding once you live in a permanent human settlement.

  11. AFell
    November 12, 2013

    Primitive humans were fairly formidable hunters, working in groups to bring down large game. But we as a species were more limited in a lot of the senses than our prey, as well as our predators. So the relationship with dogs was greatly advantageous for both humans and dogs, as dogs provided the senses human lacked, and humans provided large brains and the ability to manipulate our environment.

    As humans became more dominant, and we developed agriculture and civilization, dogs filled even more important roles in our societies. They still hunted, but now, we had perfected a lot of those hunting techniques to an art form. Additionally, we took the baser instincts that dogs are born with and honed them into the working breeds to act as shepherds to domesticated livestock.

    Even in modern society, dogs fill vital roles in almost any workplace. Their tireless hunter instincts still make them vital allies in both law enforcement and the military. Their heightened senses have yet to be surpassed by any machine we can make, and as we have adapted their breeds, we can get those senses in smaller and smaller breeds. For instance, the preferred working breed for US Customs sniffer dogs is the beagle, who has a very sensitive nose, is very hardy, intelligent and long-lived, and, when viewed by most people, is not seen as threatening. These dogs pick up on hidden contraband that humans alone would never locate, and carry with them sensitive gear that we could not replicate without an entire room full of technology.

    Wherever humans go into the future, I can see dogs going right alongside them. This journey of friendship began back in our primitive past, and will continue into the unforeseen future. Our lots are inextricably bound together, so we might as well make the best of it.

  12. Diana
    February 25, 2014

    A poster says, “The greatest mistake of mankind…”

    “Hardly. Dogs are an integral part of our history and culture… ”

    And it has been shone that with out the dog (the first domesticated animal) we could not have domesticated the rest. It was because of the dog that we were able to domesticate the second animal: sheep.

    So really if you think about it… they enabled us to become “domesticated”. Now if you think that was a mistake, you could be right. :-)

  13. threenorns
    April 11, 2014

    “trendy (and expensive) raw meat diet”

    first off, it’s a helluva lot cheaper to feed my dog meat than the junk in a bag. feeding him commercial food of the lowest quality i can tolerate runs me $45/bag. the bag is supposed to last a month but he’ll run through it in 10 days if i want to keep any meat on his bones and stop him from chewing off my leg. that’s $135 a month just for the dog.

    i buy the last day of sale meat at the grocery store or any meat that’s $3/lb or less and for $120 a month, i feed my 65lb border collie mix and five cats.

    another point: when my dog eats commercial food, no matter the quality, his stools are very loose – even sloppy – and *foul*. beyond foul, the stink is *vile*. that doesn’t happen with the raw food diet – both cat and dog poops are very mild-odoured and, far from leaving a mess on the lawn, it’s a matter of waiting a day or three until they turn white then one smack with a shovel to break them down into powder that does not burn the grass. also, no urine burns on the grass.

    add to that the unbelievable roll-call of recalls every month, even of such “high quality” brands as blue buffalo?

    sorry – raw food diet is the way to go.

Add Your Comments

All fields required.

Related Posts