Deanne Fitzmaurice / Science file

Gibson, a Great Dane, can look a pony in the eye — while Zoie, a Chihuahua, can fit into a purse.

By Charles Choi
LiveScience

Big dogs apparently die younger mainly because they age more quickly, researchers say.

These new findings could help unravel the biological links between growth and mortality, the scientists added.

Normally, across species, larger mammals live longer than their smaller counterparts. For instance, elephants can get up to 70 years old in the wild, while house mice reach only 4 years. Puzzlingly, within species, the opposite seems true — in mice, horses and perhaps even humans.

The apparent cost of bigger bodies is especially conspicuous with dogs, a species that people have bred over the millennia to come in an extraordinary range of sizes. The heaviest known dog may have been Zorba, an English mastiff that weighed 343 pounds (155 kilograms), while the smallest dog alive may be Meyzi, a terrier less than a quarter-pound (110 grams) in size.

Large breeds often die young compared with smaller ones, with a 155-pound (70-kilogram) Great Dane having an average life span of about 7 years, while a 9-pound (4-kilogram) toy poodle can expect to live up to 14 years. [The 10 Most Popular Dog Breeds]

To shed light on the possible tradeoffs of large size, researchers analyzed ages at death in 74 breeds, using data from more than 56,000 dogs that visited veterinary teaching hospitals. The researchers focused on why large dogs lived shorter lives on average.

"My main scientific interest is life-history evolution. I'm also a bit of a dog nerd in private life," said researcher Cornelia Kraus, an evolutionary biologist at the University of Göttingen in Germany.

The scientists found that large breeds apparently aged at faster rates. The speed at which the risk of death increased with age was greater with larger breeds than smaller ones. Indeed, among dog breeds, an increase of 4.4 pounds (2 kilograms) in body mass leads to a loss of approximately 1 month of life expectancy.

"Their lives seem to unwind in fast motion," Kraus told LiveScience.

The investigators now want to follow the growth and health histories of a large number of dogs and pinpoint the leading causes of death for large dogs. For instance, bigger canines apparently suffer from cancer more often, which could make sense; large dogs grow more than smaller breeds do, and cancer is rooted in abnormal cell growth.

"This research should be feasible in dogs, since I found that dog people in general seem very open, interested in and interested to contribute to research on their favorite species," Kraus said.

Kraus and her colleagues Samuel Pavard and Daniel Promislow detailed their findings in the April issue of the journal American Naturalist.

Follow LiveScience on Twitter @livescience, Facebook or Google+. Original article on LiveScience.com.

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• Album: The World's Biggest Beasts

Copyright 2013 LiveScience. All rights reserved.

Ovodov et al. / PLOS ONE

The skull of a 33,000-year-old canid was found in a cave in the Altai Mountains of southern Siberia.

By Stephanie Pappas
LiveScience

A canine skull found in the Altai Mountains of Siberia is more closely related to modern domestic dogs than to wolves, a new DNA analysis reveals.

The findings could indicate that dogs were domesticated around 33,000 years ago. The point at which wolves made the transition to man's best friend is hotly contested, though dogs were well-established in human societies by about 10,000 years ago. Dogs and humans were buried together in Germany about 14,000 years ago, a strong hint of domestication, but genetic studies have pinpointed the origin of dog domestication in both China and the Middle East.

The Altai specimen, a well-preserved skull, represents one of the two oldest possible domestic dogs ever found. Another possible domestic dog fossil, dated to approximately 36,000 years ago, was found in Goyet Cave in Belgium.

Anatomical examinations of these skulls suggest they are more doglike than wolflike. To confirm, researchers from the Russian Academy of Sciences and their colleagues drilled a tiny amount of bone from the Altai dog's incisor and jaw, and analyzed its DNA. They conducted all of the work in an isolated lab and used extra precautions to prevent contamination, as ancient DNA is extremely fragile.

The researchers then compared the genetic sequences from the Altai specimen with sequences from 72 modern dogs of 70 different breeds, 30 wolves, four coyotes and 35 prehistoric canid species from the Americas. [10 Breeds: What Your Dog Says About You]

They found that the Altai canid is more closely related to modern domestic dogs than to modern wolves, as its skull shape had previously suggested. That means that the Altai canid was an ancient dog, not an ancient wolf — though it had likely diverged from the wolf line relatively recently, the researchers report Wednesday in the journal PLOS ONE.

If the Altai dog was really domesticated, it would push back the origin of today's house pets more than 15,000 years and move the earliest domestication out of the Middle East or East Asia, as previous studies have suggested. However, the analysis was limited to only a portion of the genome, the researchers wrote.

"Additional discoveries of ancient doglike remains are essential for further narrowing the time and region of origin for the domestic dog," they said.

Follow Stephanie Pappas @sipappas. Follow LiveScience on Twitter @livescience, Facebook or Google+. Original article on LiveScience.com. 

• 10 Things You Didn't Know About Dogs
• The 10 Most Popular Dog Breeds
• Puppy Love: Test Your Dog Breed Knowledge

Authors of "Ancient DNA Analysis Affirms the Canid From Altai as a Primitive Dog" include Anna Druzhkova, Olaf Thalmann, Vladimir A. Trifonov, Jennifer A. Leonard, Nadezhda V. Vorobieva, Nikolai D. Ovodov, Alexander S. Graphodatsky and Robert K. Wayne.

Copyright 2013 LiveScience. All rights reserved.

Dognition

Duke neuroscientist Brian Hare tests a dog's cognition using a simple set of toys.

Is your dog an Einstein or a Charmer? For $60 (woof!!), a new business venture called Dognition will help you put your pooch through a series of fun playtime activities to find out how your dog thinks. The metrics generated by those experiments … I mean, fun playtime activities … are being fed into a research project that could for the first time determine how the cognitive traits of various breeds differ.

"Dognition.com is ultimately about people's dogs, and finding out about your dog," Duke University neuroscientist Brian Hare, one of the venture's co-founders, told NBC News. "That's what you're paying for. I buy fancy dog food for my dog, and just like I want to take care of his stomach, I want to take care of his mind, too. Skip the next couple of chew toys, and your dog and you will really enjoy doing something a little different."

The business venture builds on Hare's work as the director of the Duke Canine Cognition Center and an associate professor in evolutionary anthropology at Duke's Center for Cognitive Neuroscience. It also meshes with a newly published book by Hare and his wife, Vanessa Woods, titled "The Genius of Dogs."

How smart are dogs?
Don't expect Dognition's cognitive assessment to measure your pet's IQ: Hare says a dog's intelligence can't be described with a single number. (Come to think of it, the same caveat should apply to humans.)

"Because we use standardized testing in all walks of life, it leads you to believe that there's just one measure of intelligence, and there's a number, and that's it," Hare said. "But when you start studying cognitive science, and look at other species, that all starts to crumble."

It's also fruitless to try calculating whether dogs are smarter than cats, or chimps, or bonobos. "That's like trying to answer the question, 'Is a hammer better than a screwdriver?'" Hare said. Instead, he and his colleagues look at how dogs and other species address problem-solving challenges and communicate with humans. It turns out that dogs are geniuses when it comes to figuring out what humans are trying to tell them — which suggests that our world is truly going to the dogs.

"Dogs are bizarrely successful," Hare said. "They have more jobs than ever in this age of the Internet and the International Space Station."

Researchers have even argued that humans and dogs are locked in a co-evolutionary embrace that began tens of thousands of years ago. Last month, for example, one research team determined that canine digestive systems have adapted to the relatively starchy diet served up by modern humans.

How it works
Hare's research into dog cognition began back in 1995, with studies of how dogs looked for hidden treats when humans tried giving them hints. Those experiments, which are done using simple household items such as plastic cups (plus tons of treats), are laid out in Dognition's Canine Assessment Toolkit.

After you plunk your money down, Dognition's website takes you through a personality questionnaire about your dog: For example, how excited does your dog get around other dogs, grown-ups, children? Do fireworks scare your pup? Then, Dognition guides you through a battery of tests that are as fun as playing fetch, or hide-and-seek. The results are uploaded to Dognition HQ, and you get back a detailed profile of your dog's mental habits, based on where Fido's performance ends up on a chart of independent vs. social problem-solving skills.

Different areas of the chart are associated with nine different canine archetypes: Ace, Stargazer, Maverick, Charmer, Socialite, Protodog, Einstein, Expert or Renaissance Dog. That can give you something to brag about on Dognition's Facebook page, but it also can shed new light on why dogs do the things they do, or how you can get through to them better. "We've got a bunch of really fantastic trainers who have signed up to help," Hare said.

Researchers get a reward as well: The data from hundreds of Canine Assessment Tests can be correlated with breed, age and other factors. "To collect the amount of data we've taken in during our month-long beta program would have taken us a couple of years," Hare said.

Eventually, Hare and his colleagues hope to map out the substantive cognitive differences between dog breeds — differences that have not yet been studied scientifically. "The reason we don't know anything about breed differences is that we currently don't have the tools available to look at the number of dogs that would allow us to answer the interesting questions," Hare said.

Dognition could fix that. And it also could open up new possibilities for some of humanity's best friends.

"One of the things we're hoping to do is, suppose there's that dog that may not be the most attractive dog physically, but the dog is wonderfully behaved," Hare said. "What Dognition.com can do is help people understand more about what's inside that dog, and not just its physical appearance — and see that, wow, this dog is amazing."

More about dog intelligence:

• Dog's vocabulary makes her a star
• Gallery: Cat vs. dog intelligence
• The world's 10 most intelligent animals
• How smart is your dog? Give him an IQ test

Dognition offers a $59.95 Canine Assessment Toolkit as well as a $129.95 annual membership bundle that includes enhanced games and other goodies.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

Lauren Solomon / Nicholas Moore / iStockphoto

Researchers say that dogs' ability to digest starch was enhanced due to genetic changes that probably occurred in parallel with domestication thousands of years ago.

Like humans, dogs underwent genetic changes thousands of years ago to adapt to a diet with more starch, researchers report. They say the change suggests that the rise of agriculture and the domestication of dogs might have gone hand in hand — but it'll take further analysis to confirm the connection.

"All dogs studied have this change, which I'd say puts it at least a couple of thousand years back in time," lead author Erik Axelsson of Sweden's Uppsala University said in an email. "But we cannot prove that it coincided with the onset of agriculture. This is something we are continuing to work on now."

The genetic shift, reported in this week's issue of the journal Nature, emerged from a detailed, genome-wide search for differences between a group of 60 dogs and  a group of 12 wolves from around the world. Axelsson and his colleagues say this is the first such search ever done for dogs.

"Only some years ago, a study like this would have been impossible due to sequencing costs," Axelsson explained. "Now it is relatively cheap. We started this study late in 2009 — that is, these projects take time."

Co-evolution with humans
Dogs are thought to have diverged from their wolvish ancestors tens of thousands of years ago, helped along by their proximity to ancient humans. Some experts would even say that humans co-evolved with domesticated animals. Past research has shown that wild breeds such as silver foxes can be turned into docile doglike creatures over the course of just a few generations.

But what genetic changes accompanied domestication? That's what the dog-vs.-wolf comparison was all about: The international research team found 36 regions of the dog genome that showed signs of selective pressure, either because they were so different from the wolf genome, or because the genetic signature became so common among different breeds of dogs.

Nineteen of the regions had to do with nervous system function — for example, the ability to create new connections in the brain. "These findings support the hypothesis that selection for altered behavior was important during dog domestication," the researchers wrote. Other regions had to do with the binding between sperm and eggs, or anatomical structure.

Then there were 10 genes that related to starch digestion and fat metabolism. "We propose that genetic variants within these genes may have been selected to aid adaptation from a mainly carnivorous diet to a more starch-rich diet during dog domestication," Axelsson and his colleagues said.

The genetic changes enhanced a dog's ability to break down starch by secreting an enzyme known as amylase in the pancreas. Wolves don't secrete nearly as much amylase, and thus they don't tend to eat starchy foods.

Why dogs went for starch
Why would starch digestion play such a significant role in dog evolution? Researchers have previously suggested that dog domestication began when wolves were attracted to waste dumps near agricultural settlements in ancient times.

"A process of natural selection started in this new niche that favored wolves that were efficient at this process," Axelsson said. "Being an efficient scavenger included being less shy, so as not to waste energy on running away when humans approached. This idea is supported by our evidence of selection in nervous system development genes, as they are likely to have effects on behavior.

"A completely new piece to the puzzle is our finding of a more efficient starch digestion in dogs," he continued. "This could mean that efficient scavenging also included having an efficient system for processing starch. That is, only wolves that could make good use of the scarce and mixed leftovers survived to become the ancestors of dogs."

Axelsson noted that other researchers have seen signs of similar genetic changes in human populations, which apparently made it easier for ancient farmers to handle a starchier diet. "The change in humans is less obvious, which makes sense, considering we were omnivores rather than carnivores prior to the agricultural revolution," he said.

Thanks to the rapid advance of gene sequencing, similar studies can now be conducted not only for dogs, but for other domesticated animals as well. Axelsson and his colleagues conducted such a study relating to chicken domestication several years ago, and now that dogs have had their genomes done, cats can't be that far behind. "I would be surprised if people aren't working on that now," Axelsson said.

Axelsson said that he used to have a dog. ("Now, we have kids instead," he joked.)

"It definitely preferred meat, but would happily feast on, for instance, potatoes," Axelsson said. "This, by the way, is probably important to note — dogs still prefer meat, but during their evolutionary history it was crucial for their survival to adapt to a diet that included a lot of starch as well."

More about dog evolution:

• Dogs (not chimps) act most like humans
• Dogs and humans share DNA, thanks to viruses
• Gallery: How science measures up cats and dogs

In addition to Axelsson, the authors of "The Genomic Signature of Dog Domestication Reveals Adaptation to a Starch-Rich Diet" include Abhirami Ratnakumar, Maja-Louise Arendt, Khurram Maqbool, Matthew T. Webster, Michele Perloski, Olof Liberg, Jon M. Arnemo, Ake Hedhammar and Kerstin Lindblad-Toh.

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.