We humans get along great with just two legs, so it is a wonder as to why some modern organisms possess several legs. Over the course of evolution, the six legs belonging to insects have been preserved, but why? Are they necessary? Would humans be better off moving around like insects? Who knows? But if we did have six legs, all the bathrooms in the world would have to be redesigned, and this is where my knowledge on the matter used to begin and end. That is until bug experts furnished me with a few theories on the subject.
Since six legged insects have existed for hundreds of millions of years, there is no doubt that having several legs provides an adaptive advantage for all insects. The fact that insects possess six legs could signify that insects evolved from organisms with many legs. Researchers believe that the number of legs stopped at three pairs because anything less than that would not have allowed organisms possessing an exoskeleton, like insects, to move efficiently.
For small organisms more legs means greater balance during physical movement. On the other hand, a larger and taller organism can achieve greater balance by using the rest of their bodies to maintain balance during movement. For example, humans do not simply rely on their two legs to achieve balance while walking or running. Humans also integrate their back, shoulder and hip muscles to keep from falling. Also, a taller mammal has a more complex set of motor neurons that communicate impulses to the brain. These neurons may send signals to the brain quickly enough for mammals to correct their balance, while insects possess less advanced and less complex neural systems. It is likely that an insect's neurons cannot fire at the speed necessary for them to correct their balance during movement.
Have you ever encountered an insect that was stuck on its back?