Comments on Would there be any major disadvantages for a species to have six legs instead of four?
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Would there be any major disadvantages for a species to have six legs instead of four?
I want a world in which animals roam the wilderness on four legs, yet at least some of them are able to do the kind of carrying and fine handling of objects done by humans. The planet is superficially similar to Earth, but it is not Earth, and there are no humans around (at least not yet; who knows what humans might do once they figure out interstellar spaceflight...)
There seem to be basically two ways to go about reaching that goal; either give the ancestor of land life on that planet six legs, allowing for two to evolve into arms and hands in a manner similar to how those of humans evolved; or give the ancestor four legs, and have their forelimbs serve both purposes, not unlike gorillas on Earth.
For the alien feel, as well as the additional options it gives, I'm currently leaning toward six legs, the foremost two of which could evolve (or not, depending on the species) into hand-like extremities.
This is intended to be a realistic world, so the normal issues of evolutionary selection pressure apply.
Suppose that an intelligent designer is faced with the choice of, for an ancestor species, ticking the "four legs" or the "six legs" checkbox on the requisition form. What, if any, would be good reasons for them to select four legs rather than six? Or, in other words, what disadvantages would be confered to the creature by having six legs as opposed to four?
For simplicity's sake, you may assume a single ancestor species for all relevant land life on the planet, so for example "some other species would be more energy-efficient in not needing to grow an extra two limbs" does not apply. Other species on the planet may have a different number of legs (compare to how there's also spiders and caterpillars on Earth), but can be ignored for the purposes of this question.
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Given the example of the development of the scorpion, it started out as a segmented worm with a pair of legs/swimming paddles per segment. These legs later developed into a variety of appendages, such as pedipalps, mandibles, pincers, and land traversing legs.
Beetles similarly developed palps, maxilla, mandibles, wing case lifting appendages, a set of four wings or wing counter weights, and six legs. If you consider the specialization of legs into structures as mentally nimble as a scorpion's pincers or a grasshopper's wings. I don't see any inhibition for a six legged terrestrial or possibly arboreal animal in development of manipulative appendages.
If the structure of any creature has a survival advantage the species tends to retain the structure. The concept that it is too mentally taxing to control large numbers of limbs is disproved by looking at the large number of multilegged creatures with rudimentary brains. A shrimp has four sets of manipulative maxillapeds, two sets of periopeds (walking legs) and five sets of pleopods (swimming legs) and two sets of uropods (fins) in its tail. With its undeveloped microscopic brain it can coordinate all twenty six of them to work in unison to locomote, maneuver and manipulate things in its environment.
This post was sourced from https://worldbuilding.stackexchange.com/a/136559. It is licensed under CC BY-SA 4.0.
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