Why are humans or most other animals bilaterally symmetrical?
There is probably not a good answer for this question, other than, a common ancestor happened to be bilaterally symmetrical externally. Most living things are not symmetric – take plants and microbes, for instance. We are not completely bilaterally symmetrical, by the way. For instance, we are right or left handed, have one liver, one spleen, one gut/stomach, one heart and our brains have differing functions on either side.
