The very first vertebrates that walked on our planet would have possibly done this deep in the great ocean, millions of years before their later relatives moved to the land.
In 2018, scientists were shocked to find the small skatefish (Leucoraja erinacea) and some basal sharks were able to use it along the seabed using many of the same neural circuits as we use today.
It is generally thought that vertebrates first learned to walk when they began to avoid the sea about 380 million years ago. But further models based on the small skatefish – one of the most primitive animals with a backbone – point to a much deeper origin, possibly more than 400 million years ago.
Mathematicians have developed a model for investigating early bony movements in the deep sea.
The simple model they created predicts the most efficient, controlled and balanced way of walking in a neutral living environment: the best result requires the left-foot-right foot to be alternating pattern, very similar to the wobble of the little skate.
What’s more, this type of trump work requires no extra energetic cost and can be reinforced over time using a simple learning scheme.
“In the context of our model, these results suggest that, despite the large solution space underway, an alternative two-legged control strategy from left and right can be discovered and will be the optimal solution for energy-efficient propulsion,” the study writes. authors.
Finding a real example of this ancient organism is similar to discovering a “needle in a haystack”, the team admits, but they say only rudimentary bones would be needed to achieve this pattern of foot placement. After the foot-like fins developed, the ancient creature would then have to gain only minimal neuronal control over their new and improved limbs.
After four episodes of learning in the model, a one-legged movement strategy began to emerge. After 200 deliveries, a two-legged walking pattern took over. By the 600th episode, the modeled creature began to alternate between left and right steps.
The authors conducted approximately 50 cases of 5,000 deliveries, including various learning parameters and rewards. In 70 percent of all cases, the author found that the best solution matched the walking distance of the small skate.
This simple control strategy suggests that walking in the deep sea is a robust and efficient behavior similar to passive walking, such as the tortuous toy walking down a slope without requiring complicated control, just gravity.
The little skate is obviously not a completely passive plodder. Its brain cells still control six muscles for movement, but the authors say that this system uses the same principles as passive: ‘Sustained movement under a constant energy source without feedback control.’
The authors are not sure why the little skate has developed a slow walk on the seabed, but they suggest that it is more efficient and cost-effective than swimming at the same pace. Further metabolic studies on the deep-sea creatures will have to verify this idea.
Sometimes in nature, the little skater uses both his legs at the same time to “point” forward and quickly start his left-right walking pattern. This type of motion was not found in the model, but the authors believe that it may be preferred if faster acceleration is required and energy efficiency is not as important. This unusual point requires a little more work.
“The combination of a reliable environment with low gravity and a morphology with bone-body may have paved the way for bipedal passages before our ancestors moved in the water to terra firma,” says Harvard astronomer Lakshminarayanan Mahadevan. university.
“As our ancient ancestors moved to the country, the control strategy probably became more complicated. But in reliable homogeneous environments, such as the seabed, perhaps a simple strategy was all that was needed.”
To supplement this theoretical model, researchers even built a simple bipedal robot based on similar deep-sea conditions. Finally, the behavior of this robot showed striking similarities with the ideal hiker of their model. Its regular footstep pattern requires no extra energy and waves on both sides of the body for stability.
However, the robot tends to run slightly faster than what is seen in the small skate.
The authors admit that they may never have known exactly how the first passage originated, but their model helps to refine the passive dynamics and neural circuits seen in living organisms.
“Understanding how the brain, body, and environment interacted in heterogeneous aquatic and terrestrial environments probably had to include proprioceptive feedback,” the authors suggest.
“But in reliable homogeneous environments, perhaps the simple strategy quantified here was where it all began.”
The study was published in the Journal for the Royal Society Interface.