Cat vs. dog evolution
Posted: Friday, December 05, 2008 5:00 PM by Alan Boyle
Win McNamee / Getty Images
A cat and a dog come face to face during a Blessing of the Animals
ceremony at Washington National Cathedral in October 2006.
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When it comes to pursuing prey, dogs do it much more efficiently than cats. So do humans, for that matter. The fact that cats are generally considered better hunters shows that evolution doesn't always favor efficiency. It all depends on what kind of niche a species can carve out for itself.
"It is usually assumed that efficiency is what matters in evolution," Daniel Schmitt, an evolutionary anthropologist at Duke University, said in a news release about the latest dog vs. cat research. "We've found that's too simple a way of looking at evolution, because there are some animals that need to operate at high energy cost and low efficiency."
Take cats, for example. Schmitt and his colleagues videotaped six housecats (Felis catis) as they moved along a 6-yard-long runway in pursuit of food treats or toys. Then they analyzed the biomechanics of their gait in detail.
The results, published Nov. 26 in the open-access journal PLoS ONE, show that cats could reduce the muscular work required to move forward by no more than 37 percent as they pursued their "prey." In a stalking posture, the cats' efficiency was even worse.
Dogs and other species that specialize in long-distance chases can run much more efficiently, reducing their work by up to 70 percent. The researchers surmised that the feline hunting style - used by a housecat stalking a bird, or a cheetah stalking an antelope in the wild - trades off efficiency for stealth.
"These data show a previously unrecognized mechanical relationship in which crouched postures are associated with changes in footfall pattern, which are in turn related to reduced mechanical energy recovery," the researchers wrote.
When a cat slinks close to the ground, it moves its front and back ends in a relatively inefficient, self-canceling pattern that results in a smooth, flowing forward motion, Schmitt said. "If they're creeping, they're going to put this foot down, and then that foot down, and then that one, in an even fashion. We think it has to do with stability and caution," he said.
Humans vs. cats vs. dogs
Previous research has shown that humans are even better than dogs or cats at long-distance runs. In fact, Harvard anthropologist Daniel Lieberman and his colleagues have argued that the human body (with our hairless skin and sweat glands, our springy tendons and twistable torso) is uniquely suited to long-distance running under conditions that would give other animals heat stroke. That's why we're the only animals that voluntarily run marathons.
Such findings mesh with Schmitt's research into the origins of human bipedalism.
"It was only a little more than a million years ago that we developed the long-legged, striding gait in which we exchanged energy efficiently," he told me today. "Our early ancestors, 3 million years ago, walked along like apes with their knees bent, and they weren't able to exchange energy."
The news that there was a hunting-related category where dogs did better than cats came as a bit of a surprise to Leslie Lyons, an expert on cats at the University of California at Davis. "Actually, I find that kind of interesting," she told me.
But she still thinks cats hold the edge in all-around hunting skill. "Overall, they've fine-tuned their system," she said.
Are cats a breed apart?
What's not surprising is that dogs and humans are more alike in their hunting style than cats and humans would be. DNA analysis has shown that dogs and humans have co-evolved for tens of thousands of years - while cats appear to be more recent companions for the human species.
"We can somewhat argue that cats are in the domestication process right now. ... Definitely the cat domestication process is more recent, occurring once agriculture got started, maybe 8,000 to 10,000 years ago," Lyons said.
Cats are definitely a breed apart when it comes to running, Schmitt said. Most other species appear to have undergone selection for a style of locomotion that favors low-oxygen consumption and low energy use for high-yield movement. "We thought cats would be the same, but we saw that they were sacrificing this to be stealthy," he said.
Schmitt emphasized that he and his colleagues weren't trying to set off a cat vs. dog controversy ... although that kind of debate always draws a crowd. "What really excited us about this paper is less the cat vs. dog angle, but more the idea that animals need to make compromises," Schmitt said.
Feel free to weigh in on the issues raised by evolutionary biology in the comment section below. And if you want to argue over which is better, cats or dogs, I won't stop you.
The lead researcher and first author for the study in PLoS ONE is Kristin Bishop, a former postdoctoral researcher at Duke who is now at UC-Davis. The other authors are Schmitt and Anita Pai, a former Duke student who is now a medical student at Vanderbilt University.
To learn more about the faculties of felines, check out this article about the decoding of the cat genome, and this one explaining why cats probably can't taste sweets. You can also click your TV onto the National Geographic Channel to watch "Science of Cats" (airing Dec. 23) and "Science of Dogs" (airing Jan. 4).
Update for 5:50 p.m. ET: My colleague on msnbc.com's multimedia team, Jim Seida, pointed me to Scott Carrier's classic audio tale on "This American Life" about his years-long effort to run down an antelope (along with his biologist brother). The quest was aimed at proving experimentally that primitive humans could do it - and proving something else that was less scientific and more spiritual. The story spawned a book titled "Running After Antelope."
