User:Anachronist/sandbox

Millipede and centipede gaits

Millipedes walk with a gait characterized by waves of legs propagating from the back to the front, as can be seen in this 30-second video: https://www.youtube.com/watch?v=rlIwoiO24XI

Centipedes I've run across walk this way also.

However, some centipedes (such as those from the scolopendra genus) walk with a gait having leg waves propagating from front to back.

Here are simulations I made of both gaits. I modeled these with OpenSCAD. Each foot spends 50% of the time on the ground and each segment is 45° out of phase from the adjacent segment. The only difference between the two animations is the sign of the phase shift.

"Normal" back-to-front waves (like a millipede)
A centipede gait with front-to-back leg waves

I'm curious how these gaits evolved. I notice that even 4-legged creatures walk with the hind legs leading the front legs on the same side, as can be seen in the animations in the gait article. If I crawl on my hands and knees, I can crawl in either manner if I think about it, but it feels more natural for my legs to lead my arms on the same side, just like a four-legged animal.

I can see an advantage to each centipede gait:

The back-to-front gait has the feet more evenly distributed on the ground.
On the other hand, the front-to-back gait has feet more or less touching the same place, which would be useful for traversing over small obstructions.

An explanation I found in this paper from Nature, which studied scolopendra centipedes, suggests that neural impulses travel from the head to the tail, which makes intuitive sense to explain the front-to-back waves, but not the back-to-front waves. That paper also found that cutting the nerve connection between two segments impeded the propagation of impulses for a wriggling swimming motion but the legs still figured out walking from mechanical contacts in spite of being severed from the brain.

Has anybody seen any explanation for the difference? Unfortunately I was unable to find anything about this on Wikipedia. The gait article is good, but its main focus is on tetrapods. ~Anachronist (talk) 03:20, 4 July 2022 (UTC)

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