Animal Locomotion Mystery Solved: Movement Isn't Wasteful

Animals move in different ways--and some of them aren't always logical. For example, why do lizards employ side-to-side sashaying rather than merely pointing toward their goal? This type of movement seems wasteful and would likely be avoided in robot design. Now, scientists found a reason for this particular movement, revealing that this locomotion isn't as wasteful as it might seem.

"One of the things they teach you in engineering is that you can't have both stability and maneuverability at the same time," said Noah Cowan, one of the researchers, in a news release. "The Wright Brothers figured this out when they built their early airplanes. They made their planes a little unstable to get the maneuverability they needed."

When an animal or vehicle is stable, it resists changes in direction. In contrast, a maneuverable animal or vehicle has the ability to quickly change course. Engineers generally believe that a system can rely on either one property or the other--but not both. Animals, though, seem to be the exception to this particular rule.

"Animals are a lot more clever with their mechanics than we often realize," said Cowan in a news release. "By using just a little extra energy to control the opposing forces they create during those small shifts in direction, animals seem to increase both stability and maneuverability when they swim, run or fly."

In order to better understand the movement of animals, the researchers employed slow-motion video. They studied the fin movements of the tiny glass knifefish. Filming the fish at a rate of 100 frames per second, the scientists examined exactly how they used their fins to hover in the water, even when there was a current.

"What is immediately obvious in the slow-motion videos is that the fish constantly move their fins to produce opposing forces," said Eric Fortune, one of the researchers, in a news release. "This arrangement is rather counter-intuitive, like two propellers fighting against each other."

The scientists then created a mathematical model that showed the animal was improving both stability and maneuverability with this arrangement. They then tested the model by creating a robot that mimicked the fish's fin movements. In the end, they found that the model was correct and that the seemingly counterintuitive movements of animals are providing them with an advantage when it comes to movement.

The findings are published in the journal Proceedings of the National Academy of Sciences.