>>36101348The reason fore the earthly love of four limbs is because of the nature of evolution, and how difficult it is to rewire a spine-based nervous system. This is why, for example, whales and dolphins have four limbs, despite two of them being inoperable.
Evolution is not goal-driven, and builds on itself, but is not cooperative.
For a backboned creature to grow more limbs, the basic creature would have to encounter a set of circumstances in which small protrusions, then large slabs of inanimate bone, flesh, and muscle flopping around would be beneficial, then go through the process of wiring them properly.
Not so with invertebrates, who are much more free to turn this spine of chitin into a "limb" by extending a nerve cluster into it.
Basically, it was dumb luck and coincidence that vertebrate life on earth was generated with 4 limbs. A coin flip made in the same circumstances could have just as easily resulted in a two, or six limbed body plan, and if MULTIPLE conversions from invertebrate to vertebrate happened in a world, odds are actually better that they would be of differing limb plans, simply because it's less likely to roll snake eyes than it is to roll a 1, and not a 1.
