Why are people bilaterally symmetrical?

Question

Why are people bilaterally symmetrical?

Answer 1

We are not symmetrical.

Better question would be why all people assymmetrical in the same way, for example everyone has heart on the left side.

Answer 2

"Why" questions pertaining to the physical world are automatically suspect. There really is no "why" in science, just a how. The closest meaningful question to what you ask is, "what is the selective advantage of bilateral symmetry?". For that we have to go back to the Precambrian, about 500 million years ago or so. According to recent findings (ref), about 40 to 55 million years before the Cambrian, the ancestor to all animals with bilateral symmetry evolved. It was a little fellow about the size of a pinhead. During the Cambrian, an explosion of evolution took place called, appropriately enough, the "Cambrian Explosion". During that time all the modern phyla of animals with bilateral symmetry evolved from that critter or a relative. These creatures all had the advantage (unlike their competitors like star fish and coral) of having high mobility. Bilateral symmetry lends itself more readily to high mobility by undulating or paddling with fins and, later on, by balancing oneself on an even number of legs on land. It's difficult to imagine being able to get around as easily as we do without such symmetry.

Answer 3

My science teacher used herself as an example for bilateral symmetry, but she had a lazy eye, so it didn't work. It was pretty funny though.

Answer 4

Development under gravity forced all bare and simple forms of life to develop lateral symmetrical form.  By the same reason fish developed lateral symmetry but tall form, easier to distribute buoyancy and stay erect under water.  That is bare development.  Anything without gravity would develop any other form and symmetry would not be strong.

There are some other explanations about symmetrical forms would not lose control of DNA easily, but I don't like to follow such theory.