What are the advantages and disadvantages of hexapedal movement as opposed to bipedal or quadrapedal? I am designing some sapient/sentient alien species (and the requisite environments that would have shaped them). I am attempting to avoid falling into the too-easy trap of just going the Star Trek "humanoid with knobbly faces" and break the mold a little more. And because I am far to pendantic fo my own good, I'm never content to go "because it's cool" without at least making some attempt to understand the real science. My current contender is a species that would come from a six-limb pattern dominant (as opposed to a terresial large verbrate four-limb pattern). However, I don't actually know (nor have I been able to Google-fu) how insect walking patterns would scale up to larger creatures and how the gaits compare with each other. To my understanding as a lay student of natural history, the number of limbs a group developed evolutionarily was something of a "it just turned out like that" (like the number of digits on a vertebrate hand - more on this further down) chance. What I don't know is whether that would apply to a macro-scale change like this or whether, like trachea, hexpedal (or more) patterns are something that only works on smaller creatures. I.e. could you have essentially a six-legged lion (obviously the legs would be in different places, but you get my drift) or a four-legged ant that woudl function comparably to their terrestial counterparts? Further complicated this is the nominal the species would have developed a quadrupedal stance (ala Preying Mantis) wherein it would have an upright body and the forelegs would have become manipulative limbs. I'm uncertain as to whether this would mean it would have developed a (say) mammal-like limb positioning/stance, or whether, like the mantis, it would still have an insect-like one and what the relative pros and cons of the two patterns would be. (I am envisioning said creature to have evolved from a group of primarily scavengers and generalists and the upright stance would have arisen as a way to carry things over frequent floods - a bit like some theories of how human upright stance arose.) Finally, there is the question of digits. While to the best of my knowledge, as I say, the number of fingers is essentially "random chance," what I'd be most interested to learn is about thumbs. Specifically, are there any mechanical reasons why the thumb is in the inside/top of the hand and not, say, on the outside/bottom. Would having the thumb on the opposite side of a hand make any difference at all to its function? If anyone can answer some of these questions - or point me in the right direction where I might find them, I would be greatly appreciative.