Evolving Inefficiently

A new Duke study suggests that evolution can behave as differently as dogs and cats. While dogs depend on an energy-efficient style of four-footed running over long distances to catch their prey, cats seem to have evolved a profoundly inefficient gait, tailor made to creep up on a mouse or bird in slow motion.

"It is usually assumed that efficiency is what matters in evolution," says Daniel Schmitt, associate professor of evolutionary anthropology. "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."

In a report published online in the research journal Public Library of Science, Schmitt and two researchers with Duke ties—lead author and former postdoctoral researcher Kristin Bishop and Vanderbilt medical student Anita Pai '08—measured and videotaped how six housecats moved along a six-yard-long runway in pursuit of food treats or feline toys.

Long-distance chase predators like dogs can reduce the muscular work needed to move forward by as much as 70 percent by allowing their bodies to rise and fall, exchanging potential and kinetic energy with each step. In contrast, the maximum amount of work for cats is only 37 percent, and much lower than that in a stalking posture, the report found.

"Most scientists think that energetic efficiency is the currency of natural selection," says Schmitt. "Here we've shown that some animals make compromises when they have to choose between competing demands."

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