A robot that slinks along the ground and winds through water like a salamander is helping scientists understand how animals walked from aquatic environments onto land millions of years ago.
Studies of the robot show that our fishy ancestors likely used their primitive brains to make the evolutionary leap from water worlds to terra firma.
Until now, scientists had puzzled over how ancient swimmers, which used mostly body movements in the water, could recruit their limbs for land locomotion while triggering the distinctive body movements required for a typical walk.
The scientists chose the amphibious salamander as a model because the animal more closely resembles the first land-dwelling vertebrates, or animals with backbones, than any other creature living today.
"We were trying to understand what really happened during the transition from primitive fishes to amphibians, like the salamander," said Auke Ijspeert, a physicist of the Swiss Federal Institute of Technology in Lausanne, lead author of a research paper on the 33-inch-long robot.
The robot has a spinal cord modeled after a real salamander. The researchers created artificial neurons that mimic the clusters of connected spinal cord neurons in animals. These neurons played a large role in vertebrate movements back when the upper brain was less involved.
Hit the beach
Ijspeert and his colleagues learned that ocean dwellers didn't need to ditch their swim fins and evolve a completely new neural circuit to creep onto land. The transition was much simpler.
Simple changes in electrical stimulation to the robot's onboard "spinal cord" turned out to cause the transition in locomotion. Low levels of electrical stimulation sent the robot on a slow-stepping walk.
As the physicists amped up the current, the limbs sped up until they could not step any faster, at which point the limb neuron centers shut down.
With out-of-commission limbs folded backward, the salamander began snaking its body, hit the water and allowed its S-shaped crawl transform into a swift swim gait.
"We believe these couplings [between the limbs and core body] are quite strong, so that once you activate the limb oscillators they force the old circuitry to go into a new mode, which is the typical standing wave of the walking," Ijspeert told LiveScience.
"The amphibian, when it had to start walking, didn't construct a completely new walking circuit but just extended the previous circuit, which was there for swimming in primitive fishes. They just added these specific limb oscillators to become able to walk," Ijspeert explained.
The model therefore provides a potential explanation, he said, for how limb movement in perhaps all vertebrates was linked with body movements to induce the transition from water to land.
"I find it very fascinating how nature has given different responsibilities to different parts of the brain, the spinal cord being responsible for locomotion, and the upper part of the brain doesn't have to worry about what each single muscle has to do over time," Ijspeeert said.
The study is detailed in the March 9 issue of the journal Science.