Octopi are some of the weirdest animals on Earth: Incredibly smart and powerful, yet they also seem out of place with their soft, vulnerable bodies and eight arms spread akimbo. Though scientists are aware of the neurological mechanisms behind the movement of an octopus’ arms, their overall locomotive strategy has been a mystery. How do they decide which arms to use? How do they move without getting all tangled up? Now, new research from the The Hebrew University of Jerusalem sheds some light on how octopi are able to get around in such a coordinated manner.
“Octopuses use unique locomotion strategies that are different from those found in other animals,” says Binyamin Hochner of The Hebrew University of Jerusalem. “This is most likely due to their soft molluscan body that led to the evolution of ‘strange’ morphology, enabling efficient locomotion control without a rigid skeleton.”
Octopi do indeed have a strange evolutionary history. They’re most likely derived from ancestors that more closely resembled clams, with strong outer shells but practically zero locomotive capabilities. Losing the shell over time certainly had some benefits: The octopi could move freely, and evolving a body from what was essentially a snail’s foot made them powerful and flexible at the same time. Of course, losing the shell also made them vulnerable, so they evolved defense mechanisms along the way (camouflage capabilities, ink clouds, etc.).
Octopi are known to be intelligent creatures, but there was still a question of how what’s still a fairly unsophisticated creature could coordinate those eight arms when it wants to move across the sea floor or other solid object. To find out, Hochner and his colleagues poured over hours worth of individual frames of octopi in locomotion, making some remarkable discoveries. For starters, despite being bilaterally symmetrical, an octopus can move equally well in any direction, regardless of body orientation.
Even more shocking, they found that octopuses move without any discernible rhythm or pattern – there’s no “left, right, left” rhythm at play. Instead, Octopi appear to move… however they want, selecting any random combination of limbs to get the job done. The researchers believe it has to do with the way their arms cause movement. To move, an octopus extends an arm, gains purchase, and then pulls with that arm while pushing with others.
“These two together enable a mechanism whereby the central controller chooses in a moment-to-moment fashion which arms to recruit for pushing the body in an instantaneous direction,” the researchers write. That’s why, apparently the only thing an octopus has to do to move is to pick the arms it wants to use.
The researchers say it lends credence to something called the Embodied Organization concept. Typically, we think of the body developing first, and motor skills second. It makes sense – how an entity moves is limited by its physiology. However, Embodied Organization suggests that motor control and physiology actually evolve together, each influencing the other to adapt to the creature’s environment.